the pathology of influenza virus infections - scribble · anrv335-pm03-19 ari 10 december 2007...

ANRV335-PM03-19 ARI 10 December 2007 16:43

The Pathology of InfluenzaVirus InfectionsJeffery K. Taubenberger and David M. MorensNational Institute of Allergy and Infectious Diseases, National Institutes of Health,Bethesda, Maryland 20892; email: [email protected],[email protected]

Annu. Rev. Pathol. Mech. Dis. 2008. 3:499–522

First published online as a Review in Advance onOctober 15, 2007

The Annual Review of Pathology: Mechanisms ofDisease is online at pathmechdis.annualreviews.org

This article’s doi:10.1146/annurev.pathmechdis.3.121806.154316

Copyright c© 2008 by Annual Reviews.All rights reserved

1553-4006/08/0228-0499$20.00

Key Words

pandemic, pneumonia, bronchitis, alveolitis, 1918 influenza, H5N1

AbstractInfluenza viruses are significant human respiratory pathogens thatcause both seasonal, endemic infections and periodic, unpredictablepandemics. The worst pandemic on record, in 1918, killed approx-imately 50 million people worldwide. Human infections caused byH5N1 highly pathogenic avian influenza viruses have raised con-cern about the emergence of another pandemic. The histopathol-ogy of fatal influenza virus pneumonias as documented over the past120 years is reviewed here. Strikingly, the spectrum of pathologicchanges described in the 1918 influenza pandemic is not signifi-cantly different from the histopathology observed in other less lethalpandemics or even in deaths occurring during seasonal influenzaoutbreaks.

499

Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Influenza virus: anantigenically andgenetically diversegroup of viruses ofthe familyOrthomyxoviridaethat contains anegative-sense,single-stranded,segmented RNAgenome

Pandemic: a globaloutbreak caused by anew strain ofinfluenza A virus thatcontains anantigenically novelhemagglutininprotein; efficientlytransmitted fromperson to person

Pneumonia: aninflammation of thelungs (the lowerrespiratory tree)caused by a widevariety ofmicroorganisms,including bacteriaand viruses

Seasonal(interpandemic orepidemic)influenza: anoutbreak of influenzaA or influenza Bvirus occurring inannual cycles, usuallyin the winter monthsin temperate climates

Highly pathogenicavian influenza(HPAI): a variant ofavian influenza virusin which mutationsin the cleavage site ofhemagglutininproduce a virus thatcauses lethalinfections in poultry

“We regret very much the fact that an influenzavirologist is unable to live say 200 years, so that

he himself would be able to see what has developedfrom his earlier assumptions.”

J. Mulder and J.F.P. Hers: Influenza (1)

INTRODUCTION

Influenza viruses are among the most com-mon causes of human respiratory infections(2), and among the most significant becausethey cause high morbidity and mortality. In-fluenza outbreaks have apparently occurredsince at least the Middle Ages, if not sinceancient times (3). In the elderly, in infants,and in people with chronic diseases, influenzais associated with especially high mortality. Inthe United States, influenza results in approx-imately 200,000 hospitalizations and 36,000deaths in a typical endemic season (4).

In addition to annual winter outbreaks,pandemic influenza viruses occasionallyemerge (5, 6), as they have every 8 to 41 yearsfor at least several centuries. Up to 50% ofthe population can be infected in a singlepandemic year, and the number of deathscaused by influenza can dramatically exceedwhat is normally expected (7, 8).

Since 1700, there have been approximatelya dozen influenza A virus pandemics; in thepast 120 years there were pandemics in 1889,1918, 1957, and 1968 (9). The 1957 pan-demic caused 66,000 excess deaths in theUnited States (8). In 1918, the worst pan-demic in recorded history caused approxi-mately 546,000 excess deaths (675,000 totaldeaths) in the United States (6) and killed upto 50 million people worldwide (10). It is verylikely that influenza will return in pandemicform (5, 6, 9). Influenza B viruses can period-ically cause large epidemics but do not causepandemics. Influenza C viruses are endemicand sporadically cause mild respiratory dis-ease. This review concentrates primarily onthe pathology of influenza A viruses, by far themost important human influenza pathogens.

The spectrum of influenza A histopathol-ogy is variable. Because pathology stud-

ies have emphasized autopsy material, onlychanges associated with lethal outcomes andpredominantly late-stage disease have beenwell characterized. There is a broad spectrumof changes associated with influenza infec-tion, varying with both clinical picture andlength of the disease course before death. Co-incident or secondary bacterial pneumoniasare not only extremely common in severe in-fluenza but also complicate the histopatho-logic appearance. Nevertheless, the spectrumof observed pathologic changes appears tovary little from pandemic to pandemic or ininterpandemic years (1, 11–22). What sepa-rates the 1918 influenza cases from cases seenin less severe pandemics and in seasonal in-fluenza infections is not the spectrum of ob-served pathology in severe and fatal cases butthe significantly higher case fatality rate and—in the 1918 pandemic only—an unusual agedistribution of deaths. In 1918, many pre-viously healthy young adults succumbed tofatal influenza infection, whereas the elderlyhad lower than expected fatality rates. In thepast two pandemics and especially in inter-pandemic seasonal influenza cases, fatal casestended to occur in people with underlyingchronic illnesses or at the extremes of age(4, 8).

Concern about the emergence of aninfluenza pandemic caused by a highlypathogenic avian influenza (HPAI) virus ofH5N1 subtype (23–26) makes reviewing thepathology of previous pandemics relevant.Unfortunately, only three autopsy examina-tions have been reported for individuals dyingafter H5N1 infection (27, 28). Whether thetypical spectrum of influenza pathology wouldbe observed if additional pathology studieswere performed remains unclear. It has beenproposed that the pathogenesis of H5N1 in-fluenza virus infection may feature a uniquehypercytokinemia (29, 30). Data also suggestthat the H5N1 virus may replicate outside therespiratory tree (28). It is crucial for pandemicpreparedness planning that additional care-ful and complete autopsy studies of H5N1influenza viral infection be performed and

500 Taubenberger · Morens

Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


reported to answer important questions aboutnatural history, pathology, and pathogenesis.

Clinical Course of Disease

Influenza is an acute respiratory disease char-acterized in its full form by the suddenonset of high fever, coryza, cough, headache,prostration, malaise, and inflammation of theupper respiratory tree and trachea. In mostcases, pneumonic involvement is not clini-cally prominent. Acute symptoms and feveroften persist for 7 to 10 days. Weakness andfatigue may linger for weeks. Influenza usu-ally occurs in winter outbreaks or epidemics(in temperate climates). People of all agesare afflicted, but the prevalence is greatest inschool-age children; disease severity is great-est in infants, the aged, and those with under-lying illnesses. Croup (laryngotracheitis) canbe a serious complication in small children.Influenza A and B viruses are the most com-mon causes of influenza-like illness (ILI), butother pathogens also cause ILI, including in-fluenza C viruses, parainfluenza viruses, respi-ratory syncytial viruses, and Mycoplasma pneu-moniae. At the peak of an influenza epidemic,approximately one-third of isolates from pa-tients with ILI will be positive for influenza A(31).

People with chronic pulmonary or cardiacdisease, or diabetes mellitus, are at high riskof developing severe complications from in-fluenza A viruses, which may include hemor-rhagic bronchitis, pneumonia (primary viralor secondary bacterial), and death. Hemor-rhagic bronchitis and pneumonia can developwithin hours. Fulminant fatal influenza vi-ral pneumonia occasionally occurs; dyspnea,cyanosis, hemoptysis, pulmonary edema, anddeath may proceed in as little as 48 hours afterthe onset of symptoms.

Influenza A viral replication peaks approx-imately 48 hours after inoculation into thenasopharynx and declines slowly, with littlevirus shed after about six days. The virus repli-cates in both the upper and lower respiratorytract. Even after the infectious virus can no

ILI: influenza-likeillness

Bronchitis/bronchiolitis: aninflammation of thebronchi andbronchioli of therespiratory tree

NA: neuraminidase

longer be recovered, viral antigen can be de-tected in cells and secretions of infected indi-viduals for several days (2). The diagnosis ofinfluenza can be established by viral culture,demonstration of viral antigens, or demon-stration of viral genetic material (in clini-cal specimens), or rises/falls in specific anti-body titers in serum or respiratory secretions(32).

Effective measures against influenza A andB diseases include prevention of infection byeither vaccination with inactivated or live at-tenuated vaccines, or administration of an-tiviral drugs prophylactically or therapeuti-cally (33). Studies of healthy young adultshave shown influenza vaccine to be 70% to90% effective in preventing influenza A ill-ness, with moderately lower efficacy rates inthe elderly. However, vaccines normally pro-tect only for a matter of months; in anycase, continuous viral antigenic drift (grad-ually accumulating mutations that allow es-cape from population immunity) of influenzaA viruses makes once effective vaccines inef-fective after a few years’ time (34). Annual re-vaccination is thus recommended for those athigh risk. The importance of predicting theemergence of new circulating influenza strainsfor subsequent annual vaccine developmentcannot be underestimated (35). Such surveil-lance is the cornerstone of the World HealthOrganization influenza surveillance network(36).

Antiviral drugs can have both therapeu-tic and prophylactic effects, but to preventdisease they must be administered continu-ously at times of high influenza activity. Ma-trix 2 ion channel blockers (amantadine andrimantadine) are effective against influenzaA viruses, but resistant viral strains developrapidly and have been recognized in approx-imately one-third of treated patients. Themore recently developed neuraminidase (NA)inhibitors, zanamivir and oseltamivir, are ef-fective against both influenza A and B viruses.Both classes of drugs are effective in prevent-ing influenza when administered prophylacti-cally (37–42).

www.annualreviews.org • Pathology of Influenza Virus Infections 501

Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Avian influenza: agenetically andantigenically diversegroup of influenza Aviruses replicating inthe gastrointestinalor respiratory tractsof wild birds anddomestic poultry,usually causing no oronly mild symptoms

HA: hemagglutinin

Biology of Influenza Viruses

Influenza viruses (of the family Orthomyx-oviridae) are enveloped negative-strand RNAviruses with segmented genomes containingseven to eight gene segments (43). One genusincludes influenza A and B viruses, and theother comprises influenza C viruses. Thethree virus types differ in host range andpathogenicity. Type B and C influenza virusesare isolated almost exclusively from humans,although influenza B viruses have been iso-lated from seals and influenza C viruses havebeen isolated from pigs and dogs (44, 45). In-fluenza A viruses, however, infect a wide vari-ety of warm-blooded animals, including birds,swine, horses, humans, and other mammals.Avian influenza viruses in aquatic birds serveas the natural reservoir for all known subtypesof influenza A virus and probably are the ul-timate source of human pandemic influenzastrains (46). Influenza A viruses are subdividedby antigenic characterization of the hemag-glutinin (HA) and NA surface glycoproteinsthat project from the virion. Sixteen HA and9 NA subtypes are known (47).

World Health Organization guidelines forthe nomenclature of influenza viruses areas follows. First, the type of virus is desig-nated (A, B, or C), then the host (if non-human), place of isolation, isolation num-ber, and year of isolation (separated byslashes). For influenza A, HA (H1–H16)and NA (N1–9) subtypes are noted inparentheses. For example, strains includedin the most recent trivalent vaccine forthe 2006–2007 season in the United Stateswere: A/New Caledonia/20/1999 (H1N1)-like, A/Wisconsin/67/2005 (H3N2)-like, andB/Malaysia/2506/2004-like (48). The 1918pandemic virus was an H1N1 strain. Its de-scendants circulated in humans until 1957when they were replaced by an H2N2 subtypepandemic strain. H2N2 viruses circulated un-til 1968 when replaced by H3N2 viruses of the1968 pandemic. In 1977, H1N1 strains fromthe pre-1957 period reappeared, and sincethen both influenza A subtypes H3N2 andH1N1 have co-circulated in humans (46).

Influenza A and B viruses have a simi-lar structure, whereas influenza C is moredivergent. A and B type viruses containeight discrete gene segments, each of themcoding for at least one protein. They arecovered with projections of three proteins:HA, NA, and matrix 2 (M2). Influenza Cviruses have seven segments and only onesurface glycoprotein (43). Each influenzaRNA segment is encapsidated by nucleopro-teins to form ribonucleotide-nucleoproteincomplexes (43).

Influenza viruses accumulate point muta-tions during replication because their RNApolymerase complex has no proofreading ac-tivity (43). Their genes have high mutationrates (ranging from approximately 1 × 10−3 to8 × 10−3 substitutions per site per year) (49).Mutations that change amino acids in the anti-genic portions of surface glycoproteins mayproduce selective advantages for viral strainsby allowing them to evade preexisting immu-nity. The HA molecule initiates infection bybinding to receptors on specific host cells. An-tibodies against the HA protein prevent re-ceptor binding and are effective at prevent-ing re-infection with the same strain. The HAand NA can evade previously acquired im-munity by either (a) antigenic drift, in whichmutations limit or prevent antibody binding,or (b) antigenic shift, in which the virus ac-quires HA of a new subtype by reassortmentbetween two influenza A viruses (2). SixteenHA subtypes are known to exist in wild birdsand provide a source of HAs novel to humans(46, 47). The emergence in human circula-tion of an influenza strain with a novel sub-type by antigenic shift has been the cause ofthe past two influenza pandemics (in 1957 and1968); in both cases, the previously circulatingpostpandemic human virus imported an HAfrom an unidentified avian or avian-like virus(50). Although one of the absolute require-ments for a pandemic is that HA must change,the extent to which the rest of the virus canor must change is not known. In 1957, threegenes from the circulating H1N1 humaninfluenza virus were replaced by avian-like


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


genes: HA, NA, and a subunit of the poly-merase complex (PB1). In 1968, the HA andPB1 genes were similarly replaced (50, 51).The 1918 virus was recently completely se-quenced using archevirologic techniques inwhich reverse-transcriptase polymerase chainreaction (RT-PCR) for small fragments ofviral RNA were analyzed from lung tissuesof 1918 influenza victims (52–57). The 1918influenza pandemic virus has an avian-likegenome and, unlike the 1957 and 1968 viruses,is hypothesized to have arisen instead bywhole genome adaptation (6, 57–59).

Although an antigenically novel HA sub-type is a likely requirement for the emer-gence of an influenza pandemic, human in-fections with animal-adapted influenza virusof novel HA subtype have been observed inwhich the virus is not transmitted efficientlyfrom person to person, suggesting that sta-ble adaptation to humans by reassortmentor whole genome adaptation is required forthe emergence of a pandemic strain (26). Forexample, in the 1976 exposure of a limitednumber of soldiers to a swine-adapted H1N1influenza virus in Fort Dix, New Jersey, therewas one death (60, 61). In 2003, an HPAIH7N7 virus caused a poultry epizootic in theNetherlands and spread regionally. Before theepizootic was contained, at least 86 poultryworkers and three contacts had been infectedand developed conjunctivitis with or withoutan ILI. There was one fatality among thosewith direct contact to poultry (62). Similarly,two people developed influenza conjunctivi-tis during a 2004 H7N3 HPAI outbreak inCanada (63).

After reemergence in 2003, the ongoingH5N1 HPAI epizootic continued to producespillover infections in humans, causing con-cern that adaptation of this virus to humanscould cause a pandemic (26). As of April 2007,291 confirmed cases of human H5N1 infec-tion had been documented, of which 172 werefatal (64), yielding a case fatality rate of 59%.Concerns about the emergence of an H5N1pandemic virus hinges not only upon trans-mission events between infected poultry and

RT-PCR:reverse-transcriptasepolymerase chainreaction

individual humans, but also upon the develop-ment of sustained human-to-human transmis-sion. Several case clusters of H5N1 infectionshave been reported (65). Although epidemio-logic information has been limited, person-to-person transmission of H5N1 has been sug-gested in a few instances, usually involvingfamily members. It is unknown whether thisrepresents infection associated with particu-larly intimate or prolonged contact, or sharedbut unidentified host factors affecting eitherinfection risk or virus transmissibility.

The 1918 pandemic was the most lethal in-fluenza pandemic on record. Most communi-ties experienced morbidity of 25%–40%, andthe vast majority of cases were self-limited.Age-specific morbidity was similar to otherpandemics, with children under 15 years ofage experiencing the highest rates of infection(66). Clinically, the 1918 pandemic presentedgenerally the same symptoms and course as in-fluenza of other years, and, pathologically, thedisease was similar to other pandemics in thatsevere complications were confined largely tothe respiratory tract (20, 21).

However, the 1918 pandemic differedfrom other pandemics in several importantclinical and epidemiologic aspects. Althoughthe clinical course was usually self-limiting,a substantially higher percentage of cases de-veloped severe pneumonic complications. Asa result, the case mortality rate in the UnitedStates averaged 2.5%, several times higherthan the current rate. Moreover, mortalityduring the 1918 pandemic was concentratedin an unusually young age group (6). Peo-ple under the age of 65 accounted for morethan 99% of excess influenza-related deathsin 1918. In contrast, in the 1957 and 1968pandemics, people less than 65 years old ac-counted for only 36% and 48% of excessdeaths due to influenza, respectively (67). Theage group affected most severely by the 1918pandemic was that between 20 and 40 years,and this group accounted for almost half ofinfluenza deaths during the pandemic. Thereasons for these unexpected patterns remainobscure.


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


INFLUENZA PATHOLOGY

Influenza virus replicates in the epithelial cellsthroughout the respiratory tree, with virusbeing recoverable from both the upper andlower respiratory tract of people naturallyor experimentally infected (2). As histologicchanges are nonspecific, histologic analysisalone is insufficient to make a specific diag-nosis (19); diagnosis typically requires sup-porting diagnostic tests such as viral isolation,rapid diagnostic tests (including RT-PCR),serologic studies, or a biopsy or autopsy tissuesection confirmed by in situ hybridization orimmunohistochemical techniques (32). Non-fatal influenza viral infections predominantlyinvolve the upper respiratory tract and tra-chea, but fatal cases of influenza usually showevidence of pneumonia. This review concen-trates on the pathology of the lower respira-tory tract.

Tracheobronchial Changesin Influenza

Starting with the first pathological studiesof influenza associated with the 1889 pan-demic (15, 68, 69), involvement of epithe-lial cells lining the upper respiratory tracthas been universally recognized and corre-sponds to the clinical signs and symptoms ofpharyngitis and tracheobronchitis. The largenumber of autopsy studies reported duringand after the 1918 influenza pandemic allreport such changes, particularly severe tra-cheitis. Winternitz and his coworkers, how-ever, clearly recognized that the epithelium ofthe trachea, bronchi, and the pulmonary alve-oli were primary sites of influenza viral repli-cation. They were among the only observersof the 1918 pandemic to reach such a con-clusion (20). At autopsy, the almost constantcoexistence of secondary bacterial infectionsof the air passages in fatal interpandemic andpandemic influenza complicates the picture,making it difficult to ascribe observed changessolely to influenza virus infection.

In the acute stage, multifocal destruc-tion and desquamation of the pseudostrati-

fied columnar epithelium of the trachea andbronchi are characteristic. Often only a basallayer of the epithelium remains. Edema andcongestion of the submucosa are often marked(20). These changes were carefully describedby several distinguished pathologists in the af-termath of the 1918 influenza (20, 70–72). Inlater stages, Askanazy observed evidence ofepithelial regeneration with the formation ofa nonkeratinizing stratified squamous meta-plasia in 38 of 90 cases (70). Winternitz et al.(20) reported similar findings.

Lucke et al. (73) reported a series of126 autopsies performed in 1918. The tra-chea and bronchi had markedly reddened andswollen mucosal surfaces, sometimes over-laid with mucopurulent material. Hemor-rhagic tracheitis and bronchitis were observedin 50% of cases. The lumina containedlarge amounts of frothy blood-stained mate-rial. In Mulder & Hers’ (1) meticulous cy-topathologic and histopathologic examina-tions of influenza cases, based predominantlyon 1957 pandemic autopsy cases, these patho-logic changes are described in great detail.Their findings reiterate pathologic changesobserved in 1918 and are concordant with thesmaller number of influenza pathology studiespublished in recent decades.

Ciliated pseudostratified epithelium oftrachea and bronchi. Early structuralchanges caused by influenza virus in theepithelium of the upper airway are variable,including cytonecrosis initially involvingshrinkage and vacuolization, followed bydesquamation of these cells into the luminalspace. Necrotic cells may also undergophagocytosis by macrophages. These struc-tural changes to the epithelium are oftenirregularly distributed, and regions of pathol-ogy can abut areas appearing histologicallynormal. The final stage of desquamation ofthe affected epithelium frequently shows onlya single layer of flattened basalar epithelialcells covering the basement membrane. Com-plete separation of the remaining epitheliummay be a histologic artifact. An outstanding


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


feature in early stages of infection is theabsence of neutrophils in the infiltrate, butas epithelial cell necrosis occurs, these cellsmigrate in. Later stages show mononuclearinflammatory cell infiltrates in the walls ofbronchi (20).

Ducts of the mucus glands. Opie (20) andWinternitz et al. (74) both initially describedthe degeneration of epithelial cells in the tra-cheal and bronchial mucus glands in influenzainfection. As in the overlying epithelium,changes consist of cytonecrosis and desqua-mation. Mulder & Hers (1) made similar ob-servations about the 1957 pandemic.

Epithelium of the bronchioli. Changes inthe smaller airways are similar to those de-scribed above for larger airways. Goodpasture(75) described the pathology of small- andmedium-sized bronchioles in 1919. Grossly,in early cases, the epithelial linings are ery-thematous and filled with thin blood-stained

froth or fluid. In later cases, the epithelia arenecrotic. Because of the simpler structure ofthe bronchiolar epithelium, thinning and flat-tening of these cells can be more pronouncedthan in the larger airways. Complete loss ofthe epithelial layer can be seen (both cili-ated and goblet cells), often associated withthe formation of hyaline membranes at thesesites. A neutrophilic exudate may be presentin the bronchiolar lumen. The interstitiummay show congestion, edema, and an inflam-matory infiltrate. Air spaces may be filledwith edema, fibrin, and varying numbers ofneutrophils (19). Lucke et al. (73) reporteddesquamative bronchiolitis, often accompa-nied by ulceration. They noted submucosalcapillary congestion and thrombi and foundthat the bronchiolar wall was sometimes en-tirely necrotic and associated with a poly-morphonuclear cell infiltrate. Photomicro-graphs of necrotizing bronchiolitis from two1918 pandemic autopsy cases are shown inFigures 1 and 2. Opie et al. (71) describedthe profound changes in smaller bronchi andfelt that they were a characteristic feature of

Figure 1H&E-stained sectionof the lung from a1918 influenza victimshowing necrotizingbronchiolitis. Thereis necrosis of thebronchiolar wall,with submucosaledema and vascularcongestion. Theepithelial layer isdesquamating, andnecrotic epithelialcells are present inthe lumen. A mixedinflammatory cellinfiltrate is presentthroughout (originalmagnification 40×).


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Figure 2H&E-stainedsection of the lungfrom a 1918influenza victimshowingnecrotizingbronchiolitis.There is necrosisof the bronchiolarwall. The epitheliallayer isdesquamating, andnecrotic epithelialcells are present inthe lumen. A mixedinflammatory cellinfiltrate is presentthroughout(originalmagnification200×).

influenza virus infection. Common changesinclude focal epithelial necrosis to necrosisof the entire wall, peribronchial hemorrhage,and peribronchial pneumonia.

Other histologic changes. Influenza infec-tion of the epithelium of the upper airwaypassages is also associated with vascularcongestion and hyperemia, edema, and aninflammatory cell infiltration of the tunicapropria and submucosa. Infiltration of neu-trophils penetrating from capillaries intovirus-infected areas in the absence of any evi-dence of secondary bacterial infection may beobserved; however, neutrophilic infiltrationis never massive. The presence of many neu-trophils within the epithelial layer stronglysuggests a coincident or secondary bacterialinfection. A mononuclear-cell-inflammatoryinfiltrate of lymphocytes, histiocytes, andplasma cells is frequently found in the tunicapropria and submucosa of influenza-infectedairways.

In situ hybridization or immunohisto-chemical analysis for influenza virus insections of the upper airway. Studies per-formed in the 1950s and 1960s (1), andmore recent studies (12, 13), have consis-tently demonstrated the presence of influenzavirus in tracheobronchial epithelial cells. Likethe variable and multifocal histopathology,staining is usually focal. Both necrotic andhistologically-normal-appearing cells can bepositively stained. Mononuclear inflamma-tory cells may also stain positively.

Evidence of epithelial repair and regenera-tion. Mitotic activity in regenerating respira-tory epithelium can be seen focally. In 14 casesof interpandemic influenza (1947–1954) Mul-der & Hers found regeneration in 3 cases, allwith courses of 5–14 days after onset of illness.In 11 cases in which death occurred in lessthan 5 days, they found variable mitotic ac-tivity but no evidence of true regeneration ofthe epithelial layer. In pandemic material, theyfound 13 cases out of 241 with regenerating


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


epithelium (1). From these studies, and thoseof the 1918 pandemic (20), it appears likelythat in influenza infection epithelial regenera-tion starts after approximately 5 days. Chroniceffects include squamous metaplasia and in-terstitial fibrosis (19).

Influenza Virus Pneumonia

Classic histopathologic studies of influenzaautopsies have clarified the changes charac-teristic of severe influenza viral pneumonia,namely, capillary and small vessel throm-boses, interstitial edema and inflammatory in-filtrates, the formation of hyaline membranesin alveoli and alveolar ducts, varying degreesof acute intraalveolar edema and/or hemor-rhage, and diffuse alveolar damage in additionto necrotizing bronchitis and bronchiolitis.Later stages show organizing diffuse alveo-lar damage, fibrosis, epithelial regeneration,and squamous metaplasia. Secondary or coin-cident bacterial pneumonias frequently occurand complicate the pathologic picture. In suchcases, a massive infiltration of neutrophils into

alveolar air spaces is observed, and alveolarhemorrhage and edema are less pronouncedthan in primary influenza virus pneumonia(73). An example of the massive neutrophil in-filtration in acute bacterial bronchopneumo-nia is shown in Figure 3. Additional changesassociated with secondary bacterial pneumo-nias vary by causative agent and time courseto death and are not further described in thisreview.

Early pathologic descriptions of influenzapneumonia were made in the 1889 pan-demic, depicting a gross pathologic pictureof an edematous, hemorrhagic bronchop-neumonia (15, 68, 69). This fits the clini-cal picture of influenza viral pneumonia, asdescribed by Leichtenstern in 1896 (15), withpatients showing marked dyspnea and de-veloping cyanosis. Influenza viral pneumoniapatients often produce massive amounts offoamy, blood-tinged, or frankly hemorrhagicsputum (15).

Large-scale autopsy studies by promi-nent pathologists during the 1918 influenza

Figure 3H&E-stained sectionof the lung from a1918 influenzavictim showing amassive infiltrate ofneutrophils that fillsthe alveolar airspaces in earlybacterialbronchopneumonia.Alveolar capillarycongestion isprominent (originalmagnification 200×).


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Alveolitis: aninflammation of thealveoli, the air sacs ofthe lungs

pandemic first described the spectrum ofchanges associated with influenza virus pneu-monia. Never before or since have so manypathological studies of influenza pneumoniabeen described. During the 1918 pandemic,an edematous, hemorrhagic bronchopneu-monia often occurring concurrently with fo-cal bacterial pneumonia was reported by manyphysicians and pathologists, compatible withfindings reported in the aftermath of the1889 pandemic. Most notable among themare the classic 1918 pandemic studies byGoodpasture (75), Klotz (76), LeCount (14,77), MacCallum (72), Opie et al. (71, 74),Walker (78), Winternitz et al. (20), Wolbach(21), and Wolbach & Frothingham (79).

Even though the first isolation of humaninfluenza virus did not occur until 1933 (80),many pathologists had long suspected an un-derlying primary influenza viral pneumoniacould be described separately from secondarybacterial pneumonias. Many pathologists in1918 rejected the hypothesis that Bacillus(now Haemophilus) influenzae (Pfeiffer’s bacil-lus) was the causative agent of influenza be-cause in a number of series it was recoveredin only a minority of cases at autopsy (81).Wolbach performed large autopsy studies inBoston and at nearby Camp Devens duringthe pandemic (21) and in 1923 wrote,

Pathologists who have reported on the pul-monary lesions have not always endeavoredto separate the lesions due to the virus ofthe epidemic and those dependent on thecomplicating organisms. On account of thevariety of complicating organisms, manifoldgross pathologic appearances have been de-scribed, and a sharp separation between le-sions produced by the virus of the epidemicdisease and the complicating organisms hasnot been made (79).

Goodpasture similarly wrote of his autopsyexperiences in 1918:

One feels justified in formulating the opin-ion that influenza is a distinct disease,

recognizable clinically only by its epi-demiologic proportions and extreme infec-tiousness, characterized pathologically bypeculiar lesions in the lungs, and causedby an unknown virus which gains entrancethrough the respiratory tract (75).

Wolbach described the hyaline mem-branes and the diffuse alveolar damage (21).LeCount described the focal capillary andsmall vessel thromboses typical of influenzaviral pneumonia (77). MacCallum (72) andWinternitz et al. (20) confirmed the aboveobservations and described the underlyingprimary pulmonary lesion as most proba-bly caused by an unknown nonbacterial (vi-ral) agent. The histopathologic pattern thatemerged from these studies matches the mod-ern view of viral pneumonia, with changesof diffuse alveolar damage, prominent necro-sis of the alveolar epithelium, the forma-tion of hyaline membranes in dilated alve-olar ducts and alveoli, capillary thrombosiswith necrosis of the alveolar septa (necrotiz-ing alveolitis), intraalveolar hemorrhage andedema, and cells with pyknotic nuclei in thealveolar air spaces (desquamated alveolar ep-ithelial cells).

During and after the 1957 pandemic, anumber of excellent autopsy studies of in-fluenza viral infection were reported (17, 18,82, 83). In 1972, Mulder & Hers publisheda comprehensive study of changes observedin these more recent fatal influenza pneumo-nias (1), which remains the definitive sourceon influenza pathology. One difference theynoted was that acute alveolar edema was notas prominent a feature of influenza pneumo-nia as in 1918, although it was still observed.In a reexamination of autopsy material of fatalinterpandemic seasonal influenza cases from1922–1947, they reported that changes of pri-mary influenza virus pneumonia were not fre-quently observed, although changes typicalof influenza were seen in the air passages.However, most interpandemic influenza caseshad longer courses and secondary bacterialpneumonias.


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


In the 1968 pandemic, other groups alsoreported on the pathologic changes observedin fatal influenza pneumonia cases (11, 16,84). Even though overall case mortality waslow in the 1968 pandemic, as compared withthe 1957 pandemic, the same spectrum ofpathology was observed. In both the 1957 and1968 pandemics, previously healthy individu-als with no underlying chronic illnesses suc-cumbed to fatal influenza viral pneumonias.

Histopathology of Primary InfluenzaVirus Pneumonia

The alveolar epithelial cell lining is as mucha target of influenza infection as the epithe-lial covering of the bronchi and bronchi-oles. Three characteristic alveolar changesare seen in early influenza virus pneumo-nia: capillary thrombosis, focal necrosis ofthe alveolar wall, and development of hya-line membranes. Early lesions of the alve-olar epithelium are often difficult to detectbecause of the hyperemic, partly hemorrhagicedematous pneumonia that develops with in-fection (1). Alveolar lining cells also un-dergo necrotic changes and desquamation.Immunofluorescence studies documented in-fluenza virus replication in alveolar epithelialcells in 1957 pandemic cases (1).

Degenerative changes include cytoplasmicvacuolization and nuclear pyknosis. Vast num-bers of desquamated cells may be observed inthe luminal spaces of alveoli, alveolar ducts,and bronchioli together with macrophagesshowing phagocytosed cellular debris. At acertain stage in influenza virus pneumonia,alveolar cells partially or completely disappear(20, 72, 76). Late stages show the presence ofregenerating alveolar epithelium (type II alve-olar hyperplasia) (1, 19).

These cytologic changes were observed inalveolar lining cells in influenza virus pneu-monia, as described by MacCallum, in 11 of44 cases. In 8 of these 11 cases, he also ob-served hyaline membranes, whereas 4 of 11cases showed thromboses in the capillaries ofthe alveolar septa. The cytologic changes are

similar to those seen in ciliated cells of theupper air passages (72). Mulder & Hers (1)found these changes in 52 of 79 cases fromthe 1957 pandemic. In affected areas, alveolarmacrophages are sometimes present in largenumbers and may show mitotic activity. Theycan demonstrate phagocytosis of degenerate,desquamated alveolar lining cells, leukocytes,and sometimes erythrocytes. Some show de-generate changes and may also be infected pri-marily with influenza virus (supported by insitu hybridization studies).

Hyperemia of the alveolar wall causedby marked capillary congestion is invariablypresent in influenza virus pneumonia. Thealveolar septa are considerably thickened bydilatation of the alveolar capillary bed. Thisdilatation is responsible for the diffuse redcolor of the affected areas (20). Fibrinous cap-illary thrombi, first described by LeCount in1919, are found in both the walls of alveolarducts and in the alveolar septa (77). Leukocyteinfiltration of the hyperemic alveolar septais always present in the early stages of in-fluenza virus pneumonia. The leukocytes arepredominantly neutrophils and occasionallyeosinophils. Infiltration is never dense exceptin areas showing septal necrosis. When hy-peremic alveolar septa show no leukocyticinfiltration, the diagnosis of influenza pneu-monia should be doubted. Later stages ofinfluenza virus pneumonia also show inter-stitial infiltrates of mononuclear leukocytes,predominantly lymphocytes and plasma cells.Megakaryocytes lying within the capillary bedare also commonly observed (1).

Necrosis of the alveolar wall may be a re-sult of capillary thrombosis (77). The extentand number of necrotic sites vary. Necroticareas are associated with leukocytic infiltrates,exudation of fibrin, and disappearance of alve-olar lining cells. Endothelial cell necrosis withpyknotic nuclei may be observed. Hemor-rhage into the alveolar air spaces is often ob-served near necrotic areas, associated withthe exudation of plasma and strands of fib-rin. Alveolar air spaces adjacent to areas ofnecrosis of the alveolar walls usually contain


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Figure 4H&E-stainedsection of the lungfrom a 1918influenza victimshowing a patternof necrotizingalveolitis. Thealveolar walls arenecrotic, andalveolar air spacescontain edemafluid, desquamatedepithelial cells, andinflammatory cells(originalmagnification200×).

an accumulation of desquamated alveolar cells(1, 75). A photomicrograph of necrotizingalveolitis with intraalveolar edema, fibrin,inflammatory cells, and desquamated alveo-lar epithelial cells is shown in Figure 4. This1918 autopsy lung tissue sample was posi-tive by RT-PCR for influenza A virus A/NewYork/1/1918 (53).

Hyaline membranes first appear in respira-tory bronchioles and alveolar ducts, then de-velop on the alveolar walls (21), as seen ina photomicrograph from another 1918 au-topsy case (Figure 5). In later stages (usu-ally after a clinical course of approximatelyone week), hyaline membranes may occur ascoarse strands or fine strands merging into anetwork of fibrin in the alveolar air spaces.This picture of a meshwork of hyaline mem-branes within alveoli is a characteristic find-ing in fully developed influenza virus pneumo-nia. Hyaline membranes may also be observedcovering small epithelial defects in bronchioliand small bronchi.

Intraalveolar edema and hemorrhage areoutstanding features of influenza virus pneu-

monia. In general their presence is associatedwith necrosis of the alveolar wall. A number ofcases in 1918 demonstrated massive amountsof edema (see Figures 6 and 7) (20, 21), afinding less prominent in the 1957 pandemicmaterial (see Figure 8) (1). Dilatation of thealveolar ducts is also a common feature in theacute stage of fatal influenza virus pneumoniadescribed by many authors in 1918. Intraalve-olar hemorrhage is often, but not always, as-sociated with areas of necrosis of the alveolarwall. Hemorrhage can sometimes be extensiveand may be grossly visible on a cut section astiny or large hemorrhagic areas, and also be-neath the pleura (74). Large hemorrhagic ar-eas can sometimes be the result of secondarybacterial pneumonias. Wolbach & Frothing-ham (79) observed evidence of intraalveolarhemorrhage and edema and the formation ofhyaline membranes in all of his cases. Good-pasture (75) found these features in all casesdying within a few days, and in 70% of caseswith pneumonias accompanying influenza.All these cases occurred in healthy youngsoldiers or civilians. LeCount, summarizing


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Figure 5H&E-stained sectionof the lung from a1918 influenza victimshowing hyalinemembranes lining analveolar duct andadjacent alveoli. Thealveolar air spacescontain edema fluid,strands of fibrin,desquamatedepithelial cells, andinflammatory cells(originalmagnification 200×).

Figure 6H&E-stained sectionof the lung from a1918 influenzavictim showingmassive pulmonaryedema. The alveolarair spaces containedema fluid. A mildinterstitialinflammatory cellinfiltrate is alsopresent (originalmagnification 40×).


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Figure 7H&E-stainedsection of the lungfrom a 1918influenza victimshowing massivepulmonaryhemorrhage. Thealveolar air spacescontainerythrocytes.Interstitial edemaand a mildinterstitialinflammatory cellinfiltrate are alsopresent (originalmagnification40×).

findings from 200 influenza autopsies in 1918,described a massive edematous exudate inlung tissue and bronchioles on cut section. Hewrote that after the development of rigor mor-tis, this bloody edema fluid “pours out of thenostrils so as to stain a large part of the whitesheets in which bodies are wrapped” (14).

Unless successfully prevented by antibi-otics, the late stages of influenza virus pneu-monia are almost always complicated by sec-ondary bacterial pneumonia, which can alsoproduce hemorrhage. In all of the Camp De-vens autopsy cases described by Wolbach (79),bacteria were either cultured from lung tissueat autopsy or identified on sections. The earli-est death in this series was seven days after on-set. The latest had a clinical course of 32 days.

Another histologic feature of the laterstages of influenza virus pneumonia is evi-dence of repair and fibrosis. Regeneration ofthe epithelial lining of alveoli and bronchialtree with evident mitoses is frequently ob-served. Squamous metaplasia is common, andregenerating alveolar lining cells frequently

show type II pneumocyte hyperplasia. Mulder& Hers (73) described 11 cases with a clinicalcourse ranging from 8 to 21 days; in 4, ep-ithelial regeneration was found in respiratorybronchioles and adjacent alveoli, including ex-amples of mitotic figures. Interstitial fibrosisof alveolar walls is common as well. Also ob-served in late stages is erythrocyte phagocyto-sis by macrophages. In the variable spectrumof influenza virus pneumonia, different areasof the lung frequently demonstrate histologiclesions compatible with different stages of in-fection. Later stages may also show typicalchanges of organization and fibrosis, includ-ing interstitial fibrosis, and bronchiolitis oblit-erans (see Figure 9) with or without evidenceof organizing pneumonia (19, 20, 74).

Influenza Virus Pneumoniain Interpandemic, SeasonalInfluenza Cases

Note that the spectrum of pathologic changesseen in the 1918, 1957, and 1968 pandemic


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


Figure 8H&E-stained sectionof the lung from a1957 influenzavictim showingmassive pulmonaryedema andhemorrhage in earlybronchopneumonia.The alveolar airspaces contain edemafluid anderythrocytes. Abronchiole showsnecrotizingbronchiolitis withepithelialdesquamation andnecrotic epithelialcells in thebronchiolar lumen(originalmagnification 20×).

Figure 9H&E-stained sectionof the lung from a1918 influenzavictim showingbronchiolitisobliterans. Thesurrounding alveolishow edema andhemorrhage. Thereis interstitial capillarycongestion, and aperibronchiolarvessel shows athrombus (originalmagnification 40×).


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


cases, including the features of fatal primaryinfluenza virus pneumonia, has also been ob-served in fatal cases of interpandemic in-fluenza. Noble et al. (85) reported such acase in 1973 in which an open lung biopsyrevealed necrotizing bronchitis and bron-chiolitis. Yeldandi & Colby (22) reported ahistopathologic analysis of six cases with lungbiopsies. Five patients recovered (two weretreated with corticosteroids for bronchiolitisobliterans with organizing pneumonia), andone case was fatal. A biopsy showed vari-able features of influenza virus pneumoniathat included patchy fibrinous alveolar exu-dates, alveoli with hyaline membranes, inter-stitial edema, late-stage severe diffuse alveolardamage, and bronchiolar necrosis. Reparativechanges were also seen, defined as the prolifer-ation of type II alveolar pneumocytes and mildinterstitial chronic inflammatory infiltrates, aswell as organization in air spaces and the in-terstitium (22).

Guarner et al. (13) reported eight fa-tal cases of influenza infection with bothhistopathology and antiviral detection by im-munohistochemistry and in situ hybridiza-tion. Cases were divided into two groupson the basis of predominant histopathology:a tracheobronchitis group and an alveolitisgroup. The tracheobronchitis group sectionsshowed focal positive immunohistochemicalor in situ hybridization staining for influenzavirus in intact and necrotic bronchial epithe-lial cells, as well as varying degrees of ep-ithelial desquamation and necrotic debris inbronchial lumina. Three of these cases hadnecrotizing bronchitis. The second group hadalveolitis with an abundant mononuclear in-flammatory infiltrate. One case showed in-traalveolar hemorrhage. In this group, no viralantigens or nucleic acids could be detected.

In another study, Guarner et al. (12)reviewed autopsy material on 47 pediatricdeaths occurring during the 2003–2004 in-fluenza season. As in the other studies,changes were seen in the trachea and bronchi,90% of cases having submucosal congestionand 73% a mononuclear submucosal inflam-

matory infiltrate. Fifty percent of cases hadnecrosis of bronchial epithelium and sub-mucosal hemorrhage. In the lower respira-tory tree, 66% had a mononuclear interstitialinflammation and formation of hyaline mem-branes; 50% showed evidence of intraalveo-lar hemorrhage. Neutrophilic, bacterial bron-chopneumonia was also observed in 50% ofcases. Immunohistochemistry for influenzaviral antigens was positive in 57% of cases.Positive staining was observed in bronchialepithelial cells; submucosal mucus glands ofthe trachea, bronchi, bronchioli; and in sin-gle cells in alveolar lumina (thought to rep-resent sloughed bronchial epithelial cells, notalveolar lining cells). The best immunohisto-chemical staining was seen in those patientsdying in less than three days. Hemophagocy-tosis was observed in 50% of cases; the authorsspeculated that it might have been associatedwith hypercytokinemia. Hemophagocytosiswas also reported in both the 1918 and 1957pandemics (1, 20).

The lack of detection of influenza virusantigens or nucleic acids in alveolar epithelialcells is interesting, especially in cases showingalveolar epithelial cell desquamation and dif-fuse alveolar damage, but this may be relatedto the time course of these cases. Mulder &Hers (1) reported positive in situ hybridiza-tion results for influenza RNA in the 1957pandemic cases, but reported that primary in-fluenza virus pneumonia was not a commonlyobserved feature of interpandemic influenzaautopsy cases from 1942–1947.

Histopathologic Changes in H5N1Highly Pathogenic Avian InfluenzaInfections

Since 2003, 328 documented cases of humanH5N1 influenza viral infection have been re-ported (64), with 200 fatalities. To et al. (27)described the autopsy findings of two of thesix individuals who died in the initial H5N1human outbreak in Hong Kong in 1997.Both had clinical courses of greater than onemonth, with deaths attributed to multi-organ


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


failure. The findings in the respiratory treeconsisted of extensive hemorrhage, organiz-ing diffuse alveolar damage with interstitialfibrosis, and cystically dilated air spaces. Onecase showed an interstitial lymphoplasma-cytic infiltrate and scattered histiocytes withreactive hemophagocytic activity. All thesefeatures are compatible with late-stage casesdescribed by Winternitz et al. in their re-view of 1918 pandemic autopsies (20). Nei-ther case showed evidence of a secondarybacterial pneumonia. Both, however, showeda reactive hemophagocytic syndrome inhematopoietic organs, which the authors pos-tulated may have been triggered by reactivehypercytokinemia.

Uiprasertkul et al. (28) reported a singleautopsy study from a fatal case in a six-year-old boy who developed acute respiratory dis-tress and died after 17 days. In this case, therespiratory tree showed a proliferative phaseof diffuse alveolar damage, interstitial pneu-monia, focal hemorrhage, and bronchiolitis.Alveolar pneumocytes with reactive hyper-plasia were seen without evident cytopathicchanges. A secondary infection with a fungus,morphologically resembling an aspergillusspecies, was noted. No hemophagocytosis wasobserved. Immunohistochemical analysis forH5N1 detected positive staining in alveolarepithelial cells. Double staining with antibod-ies against surfactant demonstrated that thesewere type II pneumocytes. Interestingly, im-munohistochemistry stains were negative inthe tracheal epithelium. RT-PCR for replica-tive H5N1 RNA was positive not only in thelung tissue, but also in the large intestines. RT-PCR was negative in plasma and other organs.

A recent clinical study of human H5N1infections demonstrated higher cytokine andchemokine levels in peripheral blood than incontrol patients with seasonal, endemic hu-man influenza infection (29), and was highestin fatal H5N1 infections. The H5N1 caseswere also characterized by high pharyngealvirus titers, and H5N1 virus was detected inone case in the rectum, suggesting the pos-sibility of limited replication outside the res-

piratory tract. Respiratory tract cytokine andchemokine levels were not measured in thisstudy, and no comparison is possible betweenthese blood cytokine results and what wouldhave been observed in past pandemic virus in-fections such as those of 1918 and 1957.

Experimental Animal Modelsof Influenza Virus Infection

Shope isolated the first influenza A virus frompigs in 1930 (86, 87), and after the subse-quent isolation of human influenza A virusesin 1933 (80), ferrets were identified as an ex-cellent laboratory model for human influenza.In a series of landmark papers, Shope reportedon the histopathologic changes in the respira-tory tract of pigs, ferrets, and mice, describ-ing changes compatible with those in humaninfluenza virus infection, namely, desquama-tion of the ciliated epithelium of the tracheo-bronchial airways and peribronchial mononu-clear cell inflammatory infiltrates (86, 88,89). The lungs of infected pigs and ferretsshowed hyperemia and capillary congestionand mononuclear and neutrophilic inflam-matory cell infiltrates in alveolar septa (of-ten marked), necrosis and desquamation ofalveolar epithelial cells, and interstitial andintraalveolar edema. Mice were susceptibleto infection with human and swine influenzaviruses (90), but could not transmit the in-fection to other mice (89). In contrast, Shopeshowed that both ferrets and swine were ableto transmit the virus to contact animals (86,88). In 1962, Hers et al. (91) demonstrated, byin situ hybridization, viral replication in alve-olar cells in experimental influenza infectionin ferrets and mice. Although these experi-mental animal models and humans infectedwith influenza A viruses share many histologicfeatures—including evidence of viral degen-eration of alveolar lining, hyperemia and con-gestion, septal inflammatory infiltrates, theappearance of macrophages with necrotic cel-lular debris in air spaces, and intraalveolaredema and hemorrhage—human cases addi-tionally demonstrate the formation of hyalinemembranes and capillary thrombosis.


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


The use of nonhuman primates for humaninfluenza virus infection has also been recentlyreevaluated. Burnet (92) reported experimen-tal influenza virus infection of cynomol-gus monkeys (Macaca fascicularis) in 1941with a variant of A/WS/33 (H1N1). Hereported histopathologic findings of bron-chopneumonia, with necrotizing bronchioli-tis, intraalveolar edema and fibrin, and amixed inflammatory infiltrate. Murphy andcolleagues published a series of studies on ex-perimental influenza virus infection in vari-ous nonhuman primates in the 1980s (93–97). Recently, Baskin et al. (98) reported thepathology of a pigtail macaque (M. nemest-rina) infected with a contemporary humanH1N1 influenza virus, and Baas et al. (99) an-alyzed host gene expression profiles in theseanimals. They found histopathologic findingscomparable to human influenza virus pneu-monia with intraalveolar edema and intersti-tial inflammatory cell infiltrates, and changesincluding alveolar epithelial hyperplasia at dayseven.

Numerous studies have examined HPAIH5N1 viruses in experimental animal mod-els, including mice and ferrets (100–104).Studies in both animals show a similarpathologic spectrum with bronchopneumo-nia, desquamation of bronchial and bronchi-olar epithelial cells, diffuse alveolar intersti-tial inflammation, intraalveolar edema, andalveolar pneumocyte hyperplasia. Immuno-histochemical analysis for the distributionof viral antigens shows positive staining inbronchial epithelial cells, alveolar pneumo-cytes, and alveolar macrophages. In both sys-tems, viral encephalitis was also observed.Kuiken et al. (105) reported on the pathologyof cynomolgus monkeys with a 1997 H5N1virus. The histopathologic changes in themonkeys included extensive desquamation ofbronchiolar and alveolar epithelium, inter-stitial inflammation and edema, intraalveolaredema, and hemorrhage admixed with numer-ous neutrophils and macrophages. One an-imal showed diffuse alveolar hyaline mem-

brane formation. Upper airway changes wereof a mild nature, but showed focal epithelialdesquamation, ulceration, and inflammation.

With the completion of the project tosequence the 1918 influenza virus genomefrom autopsy tissues of 1918 influenza victims(57), it has become possible using reverse ge-netic techniques (106) to produce infectiousviruses containing the 1918 influenza virusopen reading frames (107–109) and to studyexperimental animal infections using mouseand cynomolgus monkey models. In both an-imals, the 1918 influenza virus replicated tohigh titers. In mice, infection with the 1918virus produced a necrotizing bronchitis andbronchiolitis with a marked alveolitis, withinfiltrates of neutrophils and macrophages.Alveolar edema was also observed. No ev-idence of systemic (nonrespiratory system)infection was noted. Gene expression arrayanalysis demonstrated a marked activation ofpre-inflammatory and cell death pathways oneday after infection (108). In the monkeys, in-fection with the reconstructed 1918 influenzavirus produced a fatal acute respiratory dis-tress syndrome (109). Gene expression arrayanalysis in this case demonstrated a dysregu-lation of the innate immune response and thatthe response was insufficient for protection.

CONCLUSION

Influenza viruses continue to be a major healththreat in both endemic and pandemic forms.The rapid, continuous, and unpredictable na-ture of influenza viral evolution makes vaccinestrategies and pandemic planning difficult. Itis crucial that future pathology studies be per-formed on autopsies of victims with fatal in-fluenza infections, whether caused by endemicstrains, seasonal strains, or zoonotic strainssuch as the recent H5N1 viruses. Careful anal-ysis of the histopathological changes of in-fection coupled with molecular genetic, vi-rologic, and immunologic analyses will con-tribute to our understanding of the variablepathogenesis of influenza viruses.


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


SUMMARY POINTS

1. Influenza viruses are common respiratory pathogens in humans.

2. Influenza viruses can cause serious infections, leading to the development of pneu-monia.

3. Influenza A viruses, because of their host-range diversity, their genetic and antigenicdiversity, and their ability to reassort genetically, are continual sources of novel in-fluenza viruses that lead to the emergence of periodic pandemics.

4. Pandemic influenza viruses cause much higher morbidity and mortality than annual,epidemic influenza virus outbreaks.

5. Influenza virus infection includes both upper and lower respiratory tract involvement.Influenza virus pneumonia, either alone or with secondary bacterial pneumonias, canoften be fatal.

6. The worst influenza pandemic on record, the 1918 influenza, killed up to 50 millionpeople globally.

7. The pathologic spectrum of fatal influenza virus infections during the 1918 pandemicwas not significantly different from that observed in other pandemics or even fromfatal cases in seasonal influenza outbreaks.

DISCLOSURE STATEMENT

The authors are not aware of any biases that might be perceived as affecting the objectivity ofthis review.

ACKNOWLEDGMENTS

This research was supported by the National Institute of Allergy and Infectious Diseases, adivision of the Intramural Research Program of the National Institutes of Health.

LITERATURE CITED

1. Mulder J, Hers JFP. 1972. Influenza. Groningen: Wolters-Noordhoff. 287 pp.2. Wright PF, Neumann G, Kawaoka Y. 2007. Orthomyxoviruses. In Fields Virology, ed.

DM Knipe, PM Howley, pp. 1691–740. Phladelphia: Lippincott Williams & Wilkins.5th ed.

3. Hirsch A. 1883. Handbook of Geographical and Historical Pathology. London: New SydenhamSoc.

4. Thompson WW, Shay DK, Weintraub E, Brammer L, Cox N, et al. 2003. Mortalityassociated with influenza and respiratory syncytial virus in the United States. JAMA289:179–86

5. Cox NJ, Subbarao K. 2000. Global epidemiology of influenza: past and present. Annu.Rev. Med. 51:407–21

6. Taubenberger JK, Morens DM. 2006. 1918 influenza: the mother of all pandemics. Emerg.Infect. Dis. 12:15–22

7. Beveridge W. 1977. Influenza: The Last Great Plague, an Unfinished Story. New York:Prodist


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


8. Simonsen L. 1999. The global impact of influenza on morbidity and mortality. Vaccine17(Suppl. 1):S3–10

9. Morens DM, Fauci AS. 2007. The 1918 influenza pandemic: insights for the 21st century.J. Infect. Dis. 195:1018–28

10. Johnson NP, Mueller J. 2002. Updating the accounts: global mortality of the 1918–1920“Spanish” influenza pandemic. Bull. Hist. Med. 76:105–15

11. Finckh ES, Bader L. 1974. Pulmonary damage from Hong Kong influenza. Aust. N.Z. J.Med. 4:16–22

12. Guarner J, Paddock CD, Shieh WJ, Packard MM, Patel M, et al. 2006. Histopathologicand immunohistochemical features of fatal influenza virus infection in children duringthe 2003–2004 season. Clin. Infect. Dis. 43:132–40

13. Guarner J, Shieh WJ, Dawson J, Subbarao K, Shaw M, et al. 2000. Immunohistochemicaland in situ hybridization studies of influenza A virus infection in human lungs. Am. J.Clin. Pathol. 114:227–33

14. LeCount ER. 1919. The pathologic anatomy of influenzal bronchopneumonia. JAMA72:650–52

15. Leichtenstern O. 1896. Influenza. I. Geschichte, Epidemiologie und Aetiologie der In-fluenza. II. Pathologie und Therapie der Influenza. In Nothnagel’s Spezielle Pathologie undTherapie, ed. H Nothnagel, pp. 1–195. Vienna: Alfred Holder

16. Lindsay MI Jr, Herrmann EC Jr, Morrow GW Jr, Brown AL Jr. 1970. Hong Konginfluenza: clinical, microbiologic, and pathologic features in 127 cases. JAMA 214:1825–32

17. Louria DB, Blumenfeld HL, Ellis JT, Kilbourne ED, Rogers DE. 1959. Studies oninfluenza in the pandemic of 1957–1958. II. Pulmonary complications of influenza.J. Clin. Invest. 38:213–65

18. Petersdorf RG, Fusco JJ, Harter DH, Albrink WS. 1959. Pulmonary infections compli-cating Asian influenza. AMA Arch. Intern. Med. 103:262–72

19. Travis WD, Colby TV, Koss MN, Rosado-de-Christenson ML, Muller NL, TalmadgeEK Jr. 2002. Non-Neoplastic Disorders of the Lower Respiratory Tract. Washington, DC: Am.Regist Pathol. Armed Forces Inst. Pathol.

20. Winternitz MC, Wason IM, McNamara FP. 1920. The Pathology of Influenza. New Haven:Yale Univ. Press

21. Wolbach SB. 1919. Comments on the pathology and bacteriology of fatal influenza cases,as observed at Camp Devens, Mass. Johns Hopkins Hosp. Bull. 30:104–9

22. Yeldandi AV, Colby TV. 1994. Pathologic features of lung biopsy specimens from in-fluenza pneumonia cases. Hum. Pathol. 25:47–53

23. Peiris JS, Yu WC, Leung CW, Cheung CY, Ng WF, et al. 2004. Re-emergence of fatalhuman influenza A subtype H5N1 disease. Lancet 363:617–19

24. Webby RJ, Webster RG. 2003. Are we ready for pandemic influenza? Science 302:1519–2225. Webster RG, Govorkova EA. 2006. H5N1 influenza: continuing evolution and spread.

N. Engl. J. Med. 355:2174–7726. Taubenberger JK, Morens DM, Fauci AS. 2007. The next influenza pandemic: Can it be

predicted? JAMA 297:2025–7227. To KF, Chan PK, Chan KF, Lee WK, Lam WY, et al. 2001. Pathology of fatal human

infection associated with avian influenza A H5N1 virus. J. Med. Virol. 63:242–4628. Uiprasertkul M, Puthavathana P, Sangsiriwut K, Pooruk P, Srisook K, et al. 2005. In-

fluenza A H5N1 replication sites in humans. Emerg. Infect. Dis. 11:1036–41


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


29. de Jong MD, Simmons CP, Thanh TT, Hien VM, Smith GJ, et al. 2006. Fatal outcomeof human influenza A (H5N1) is associated with high viral load and hypercytokinemia.Nat. Med. 12:1203–7

30. Peiris M. 2006. Pathogenesis of avian flu H5N1 and SARS. Novartis Found Symp. 279:56–60; discussion 60–65, 216–19

31. Cent. Dis. Control. 2000. Update: influenza activity: United States and worldwide, 1999–2000 season, and composition of the 2000–01 influenza vaccine. MMWR Morb. Mortal.Wkly. Rep. 49:375–81

32. Taubenberger JK, Layne SP. 2001. Diagnosis of influenza virus: coming to grips with themolecular era. Mol. Diagn. 6:291–305

33. Couch RB. 2000. Prevention and treatment of influenza. N. Engl. J. Med. 343:1778–8734. Hay AJ, Gregory V, Douglas AR, Lin YP. 2001. The evolution of human influenza viruses.

Philos. Trans. R. Soc. Lond. B Biol. Sci. 356:1861–7035. Gensheimer KF, Meltzer MI, Postema AS, Strikas RA. 2003. Influenza pandemic pre-

paredness. Emerg. Infect. Dis. 9:1645–4836. World Health Org. 2001. Influenza in the world. 1 October 1999–30 September 2000.

Wkly. Epidemiol. Rec. 76:49–5337. Hayden FG. 1999. Update on influenza and rhinovirus infections. Adv. Exp. Med. Biol.

458:55–6738. Monto AS, Robinson DP, Herlocher ML, Hinson JM Jr, Elliott MJ, Crisp A. 1999.

Zanamivir in the prevention of influenza among healthy adults: a randomized controlledtrial. JAMA 282:31–35

39. Hayden FG. 2006. Antiviral resistance in influenza viruses: implications for managementand pandemic response. N. Engl. J. Med. 354:785–88

40. Hayden FG. 2006. Antivirals for influenza: historical perspectives and lessons learned.Antiviral Res. 71:372–78

41. Hayden FG, Pavia AT. 2006. Antiviral management of seasonal and pandemic influenza.J. Infect. Dis. 194(Suppl. 2):S119–26

42. Monto AS, McKimm-Breschkin JL, Macken C, Hampson AW, Hay A, et al. 2006. De-tection of influenza viruses resistant to neuraminidase inhibitors in global surveillanceduring the first 3 years of their use. Antimicrob. Agents Chemother. 50:2395–402

43. Palese P, Shah ML. 2007. Orthomyxoviridae: the viruses and their replication. In FieldsVirology, ed. DM Knipe, PM Howley, pp. 1647–90. Philadelphia: Lippincott, Williams& Wilkins. 5th ed.

44. Osterhaus AD, Rimmelzwaan GF, Martina BE, Bestebroer TM, Fouchier RA. 2000.Influenza B virus in seals. Science 288:1051–53

45. Youzbashi E, Marschall M, Chaloupka I, Meier-Ewert H. 1996. [Distribution of influenzaC virus infection in dogs and pigs in Bavaria]. Tierarztl. Prax 24:337–42

46. Webster RG, Bean WJ, Gorman OT, Chambers TM, Kawaoka Y. 1992. Evolution andecology of influenza A viruses. Microbiol. Rev. 56:152–79

47. Obenauer JC, Denson J, Mehta PK, Su X, Mukatira S, et al. 2006. Large-scale sequenceanalysis of avian influenza isolates. Science 311:1576–80

48. Smith NM, Bresee JS, Shay DK, Uyeki TM, Cox NJ, Strikas RA. 2006. Prevention andcontrol of influenza: recommendations of the Advisory Committee on ImmunizationPractices (ACIP). MMWR Recomm. Rep. 55:1–42

49. Chen R, Holmes EC. 2006. Avian influenza virus exhibits rapid evolutionary dynamics.Mol. Biol. Evol. 23:2336–41

50. Scholtissek C, Rohde W, Von Hoyningen V, Rott R. 1978. On the origin of the humaninfluenza virus subtypes H2N2 and H3N2. Virology 87:13–20


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


51. Kawaoka Y, Krauss S, Webster RG. 1989. Avian-to-human transmission of the PB1 geneof influenza A viruses in the 1957 and 1968 pandemics. J. Virol. 63:4603–8

52. Basler CF, Reid AH, Dybing JK, Janczewski TA, Fanning TG, et al. 2001. Sequence ofthe 1918 pandemic influenza virus nonstructural gene (NS) segment and characterizationof recombinant viruses bearing the 1918 NS genes. Proc. Natl. Acad. Sci. USA 98:2746–51

53. Reid AH, Fanning TG, Hultin JV, Taubenberger JK. 1999. Origin and evolution of the1918 “Spanish” influenza virus hemagglutinin gene. Proc. Natl. Acad. Sci. USA 96:1651–56

54. Reid AH, Fanning TG, Janczewski TA, Lourens RM, Taubenberger JK. 2004. Novelorigin of the 1918 pandemic influenza virus nucleoprotein gene. J. Virol. 78:12462–70

55. Reid AH, Fanning TG, Janczewski TA, McCall S, Taubenberger JK. 2002. Characteri-zation of the 1918 “Spanish” influenza virus matrix gene segment. J. Virol. 76:10717–23

56. Reid AH, Fanning TG, Janczewski TA, Taubenberger JK. 2000. Characterization of the1918 “Spanish” influenza virus neuraminidase gene. Proc. Natl. Acad. Sci. USA 97:6785–90

57. Taubenberger JK, Reid AH, Lourens RM, Wang R, Jin G, Fanning TG. 2005. Charac-terization of the 1918 influenza virus polymerase genes. Nature 437:889–93

58. Reid AH, Taubenberger JK, Fanning TG. 2004. Evidence of an absence: the geneticorigins of the 1918 pandemic influenza virus. Nat. Rev. Microbiol. 2:909–14

59. Rabadan R, Levine AJ, Robins H. 2006. Comparison of avian and human influenza Aviruses reveals a mutational bias on the viral genomes. J. Virol. 80:11887–91

60. Gaydos JC, Top FH Jr, Hodder RA, Russell PK. 2006. Swine influenza a outbreak, FortDix, New Jersey, 1976. Emerg. Infect. Dis. 12:23–28

61. Sencer DJ, Millar JD. 2006. Reflections on the 1976 swine flu vaccination program.Emerg. Infect. Dis. 12:29–33

62. Fouchier RA, Schneeberger PM, Rozendaal FW, Broekman JM, Kemink SA, et al. 2004.Avian influenza A virus (H7N7) associated with human conjunctivitis and a fatal case ofacute respiratory distress syndrome. Proc. Natl. Acad. Sci. USA 101:1356–61

63. Tweed SA, Skowronski DM, David ST, Larder A, Petric M, et al. 2004. Human illnessfrom avian influenza H7N3, British Columbia. Emerg. Infect. Dis. 10:2196–99

64. World Health Org. 2007. Cumulative Number of Confirmed Human Cases of Avian InfluenzaA/(H5N1) Reported to WHO. Geneva: World Health Org.

65. Ungchusak K, Auewarakul P, Dowell SF, Kitphati R, Auwanit W, et al. 2005. Probableperson-to-person transmission of avian influenza A (H5N1). N. Engl. J. Med. 352:333–40

66. Jordan EO. 1927. Epidemic Influenza: A Survey. Chicago: Am. Med. Assoc.67. Simonsen L, Clarke MJ, Schonberger LB, Arden NH, Cox NJ, Fukuda K. 1998. Pandemic

versus epidemic influenza mortality: a pattern of changing age distribution. J. Infect. Dis.178:53–60

68. Weichselbaum A. 1892. Beitrag zur Aetiologie und pathologischen Antatomie der In-fluenza. Wiener klinische Wochenschr. 5:459–61

69. Kuskow N. 1895. Zur pathologischen Anatomie der Grippe. Virchow’s Arch. Pathol. Anat.139:406

70. Askanazy M. 1919. Ueber die Veranderungen der grossen Luftwege, besonders ihreEpithel-Metaplasie bei der Influenza. Corr. Bl. Schwiez Aerzte 49:465

71. Opie EL, Blake FG, Small JC, Rivers TM. 1921. Epidemic Respiratory Disease: The Pneu-monias and Other Infections of the Respiratory Tract Accompanying Influenza and Measles. St.Louis: C.V. Mosby Co.

72. MacCallum WG. 1921. Pathological anatomy of pneumonia associated with influenza.Johns Hopkins Hosp. Rep. 20:149

73. Lucke B, Wight T, Kime E. 1919. Pathologic anatomy and bacteriology of influenza.Arch. Intern. Med. 24:154–237


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


74. Opie EL. 1928. The pathologic anatomy of influenza. Arch. Pathol. Lab. Med. 5:285–30375. Goodpasture EW. 1919. The significance of certain pulmonary lesions in relation to the

etiology of influenza. Am. J. Med. Sci. 158:863–7076. Klotz O. 1919. The pathology of epidemic influenza. In Studies on Epidemic Influenza, ed.

O Klotz, pp. 207–93. Pittsburgh: Univ. Pittsburgh Sch. Med.77. LeCount ER. 1919. Disseminated necrosis o the pulmonary capillaries in influenzal pneu-

monia. J. Am. Med. Assoc. 72:1519–2078. Walker OJ. 1919. Pathology of influenza-pneumonia. J. Lab. Clin. Med. 5:15479. Wolbach SB, Frothingham C. 1923. The influenza epidemic at Camp Devens in 1918.

Arch. Intern. Med. 32:571–60080. Smith W, Andrewes C, Laidlaw P. 1933. A virus obtained from influenza patients. Lancet

2:66–6881. Taubenberger JK, Hultin JV, Morens DM. 2007. Discovery and characterization of the

1918 pandemic influenza virus in historical context. Antivir. Ther. 12:581–9182. Hers JF, Goslings WR, Masurel N, Mulder J. 1957. Death from Asiatic influenza in the

Netherlands. Lancet 273:1164–6583. Hers JF, Masurel N, Mulder J. 1958. Bacteriology and histopathology of the respiratory

tract and lungs in fatal Asian influenza. Lancet 2:1141–4384. Feldman PS, Cohan MA, Hierholzer WJ Jr. 1972. Fatal Hong Kong influenza: a clinical,

microbiological and pathological analysis of nine cases. Yale J. Biol. Med. 45:49–6385. Noble RL, Lillington GA, Kempson RL. 1973. Fatal diffuse influenzal pneumonia: pre-

mortem diagnosis by lung biopsy. Chest 63:644–6686. Shope RE. 1931. Swine influenza. I. Experimental tranmission and pathology. J. Exp.

Med. 54:349–5987. Shope RE. 1931. Swine influenza. III. Filtration experiments and etiology. J. Exp. Med.

54:373–8588. Shope RE. 1934. The infection of ferrets with swine influenza virus. J. Exp. Med. 60:49–6189. Shope RE. 1935. The infection of mice with swine influenza virus. J. Exp. Med. 62:561–7290. Andrewes CH, Laidlaw PP, Smith W. 1934. The susceptibility of mice to the viruses of

human and swine influenza. J. Exp. Med. 224:859–6291. Hers JF, Mudler J, Masurel N, van der Kuip L, Tyrrell DA. 1962. Studies on the patho-

genesis of influenza virus pneumonia in mice. J. Pathol. Bacteriol. 83:207–1792. Burnet FM. 1941. Influenza virus “A” infections of cynomolgus monkeys. Aust. J. Exp.

Biol. 19:281–9093. Clements ML, Snyder MH, Buckler-White AJ, Tierney EL, London WT, Murphy

BR. 1986. Evaluation of avian-human reassortant influenza A/Washington/897/80×A/Pintail/119/79 virus in monkeys and adult volunteers. J. Clin. Microbiol. 24:47–51

94. Snyder MH, Clements ML, Herrington D, London WT, Tierney EL, Murphy BR.1986. Comparison by studies in squirrel monkeys, chimpanzees, and adult humans ofavian-human influenza A virus reassortants derived from different avian influenza virusdonors. J. Clin. Microbiol. 24:467–69

95. Snyder MH, London WT, Maassab HF, Murphy BR. 1989. Attenuation and phenotypicstability of influenza B/Texas/1/84 cold-adapted reassortant virus: studies in hamsters andchimpanzees. J. Infect. Dis. 160:604–10

96. Snyder MH, London WT, Tierney EL, Maassab HF, Murphy BR. 1986. Restrictedreplication of a cold-adapted reassortant influenza A virus in the lower respiratory tractof chimpanzees. J. Infect. Dis. 154:370–71


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.


97. Snyder MH, Stephenson EH, Young H, York CG, Tierney EL, et al. 1986. Infectivity andantigenicity of live avian-human influenza A reassortant virus: comparison of intranasaland aerosol routes in squirrel monkeys. J. Infect. Dis. 154:709–11

98. Baskin CR, Garcia-Sastre A, Tumpey TM, Bielefeldt-Ohmann H, Carter VS, et al. 2004.Integration of clinical data, pathology, and cDNA microarrays in influenza virus-infectedpigtailed macaques (Macaca nemestrina). J. Virol. 78:10420–32

99. Baas T, Baskin CR, Diamond DL, Garcia-Sastre A, Bielefeldt-Ohmann H, et al. 2006.Integrated molecular signature of disease: analysis of influenza virus-infected macaquesthrough functional genomics and proteomics. J. Virol. 80:10813–28

100. Maines TR, Chen LM, Matsuoka Y, Chen H, Rowe T, et al. 2006. Lack of transmissionof H5N1 avian-human reassortant influenza viruses in a ferret model. Proc. Natl. Acad.Sci. USA 103:12121–26

101. Maines TR, Lu XH, Erb SM, Edwards L, Guarner J, et al. 2005. Avian influenza (H5N1)viruses isolated from humans in Asia in 2004 exhibit increased virulence in mammals.J. Virol. 79:11788–800

102. Mase M, Tanimura N, Imada T, Okamatsu M, Tsukamoto K, Yamaguchi S. 2006. RecentH5N1 avian influenza A virus increases rapidly in virulence to mice after a single passagein mice. J. Gen. Virol. 87:3655–59

103. Nishimura H, Itamura S, Iwasaki T, Kurata T, Tashiro M. 2000. Characterization ofhuman influenza A (H5N1) virus infection in mice: neuro-, pneumo- and adipotropicinfection. J. Gen. Virol. 81:2503–10

104. Salomon R, Franks J, Govorkova EA, Ilyushina NA, Yen HL, et al. 2006. The polymerasecomplex genes contribute to the high virulence of the human H5N1 influenza virus isolateA/Vietnam/1203/04. J. Exp. Med. 203:689–97

105. Kuiken T, Rimmelzwaan GF, Van Amerongen G, Osterhaus AD. 2003. Pathology ofhuman influenza A (H5N1) virus infection in cynomolgus macaques (Macaca fascicularis).Vet. Pathol. 40:304–10

106. Fodor E, Devenish L, Engelhardt OG, Palese P, Brownlee GG, Garcia-Sastre A. 1999.Rescue of influenza A virus from recombinant DNA. J. Virol. 73:9679–82

107. Tumpey TM, Basler CF, Aguilar PV, Zeng H, Solorzano A, et al. 2005. Characterizationof the reconstructed 1918 Spanish influenza pandemic virus. Science 310:77–80

108. Kash JC, Tumpey TM, Proll SC, Carter V, Perwitasari O, et al. 2006. Genomic analysis ofincreased host immune and cell death responses induced by 1918 influenza virus. Nature443:578–81

109. Kobasa D, Jones SM, Shinya K, Kash JC, Copps J, et al. 2007. Aberrant innate immuneresponse in lethal infection of macaques with the 1918 influenza virus. Nature 445:319–23


Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.

AR335-FM ARI 10 December 2007 18:20

Annual Reviewof Pathology:Mechanismsof Disease

Volume 3, 2008Contents

The Relevance of Research on Red Cell Membranes to theUnderstanding of Complex Human Disease: A Personal PerspectiveVincent T. Marchesi � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �1

Molecular Mechanisms of Prion PathogenesisAdriano Aguzzi, Christina Sigurdson, and Mathias Heikenwalder � � � � � � � � � � � � � � � � � � � � 11

The Aging BrainBruce A. Yankner, Tao Lu, and Patrick Loerch � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 41

Gene Expression Profiling of Breast CancerMaggie C.U. Cheang, Matt van de Rijn, and Torsten O. Nielsen � � � � � � � � � � � � � � � � � � � � � � 67

The Inflammatory Response to Cell DeathKenneth L. Rock and Hajime Kono � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 99

Molecular Biology and Pathogenesis of Viral MyocarditisMitra Esfandiarei and Bruce M. McManus � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �127

Pancreatic CancerAnirban Maitra and Ralph H. Hruban � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �157

Kidney Transplantation: Mechanisms of Rejection and AcceptanceLynn D. Cornell, R. Neal Smith, and Robert B. Colvin � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �189

Metastatic Cancer CellMarina Bacac and Ivan Stamenkovic � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �221

Pathogenesis of Thrombotic MicroangiopathiesX. Long Zheng and J. Evan Sadler � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �249

Anti-Inflammatory and Proresolving Lipid MediatorsCharles N. Serhan, Stephanie Yacoubian, and Rong Yang � � � � � � � � � � � � � � � � � � � � � � � � � � � � �279

Modeling Morphogenesis and Oncogenesis in Three-DimensionalBreast Epithelial CulturesChristy Hebner, Valerie M. Weaver, and Jayanta Debnath � � � � � � � � � � � � � � � � � � � � � � � � � � � �313

v

Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.

AR335-FM ARI 10 December 2007 18:20

The Origins of Medulloblastoma SubtypesRichard J. Gilbertson and David W. Ellison � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �341

Molecular Biology and Pathology of LymphangiogenesisTerhi Karpanen and Kari Alitalo � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �367

Endoplasmic Reticulum Stress in Disease PathogenesisJonathan H. Lin, Peter Walter, and T.S. Benedict Yen � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �399

Autophagy: Basic Principles and Relevance to DiseaseMondira Kundu and Craig B. Thompson � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �427

The Osteoclast: Friend or Foe?Deborah V. Novack and Steven L. Teitelbaum � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �457

Applications of Proteomics to Lab DiagnosisRaghothama Chaerkady and Akhilesh Pandey � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �485

The Pathology of Influenza Virus InfectionsJeffrey K. Taubenberger and David M. Morens � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �499

Airway Smooth Muscle in AsthmaMarc B. Hershenson, Melanie Brown, Blanca Camoretti-Mercado,and Julian Solway � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �523

Molecular Pathobiology of Gastrointestinal Stromal SarcomasChristopher L. Corless and Michael C. Heinrich � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �557

Notch Signaling in LeukemiaJon C. Aster, Warren S. Pear, and Stephen C. Blacklow � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �587

The Role of Hypoxia in Vascular Injury and RepairTony E. Walshe and Patricia A. D’Amore � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �615

Indexes

Cumulative Index of Contributing Authors, Volumes 1–3 � � � � � � � � � � � � � � � � � � � � � � � � � � �645

Cumulative Index of Chapter Titles, Volumes 1–3 � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �647

Errata

An online log of corrections to Annual Review of Pathology: Mechanisms of Diseasearticles may be found at http://pathol.annualreviews.org

vi Contents

Ann

u. R

ev. P

atho

l. M

ech.

Dis

. 200

8.3:

499-

522.

Dow

nloa

ded

from

ww

w.a

nnua

lrev

iew

s.or

gby

Uni

vers

ity o

f M

isso

uri -

Col

umbi

a on

09/

20/1

3. F

or p

erso

nal u

se o

nly.

the pathology of influenza virus infections - scribble · anrv335-pm03-19 ari 10 december 2007...

Documents