Fleas & Plague

Announcements

• Should have Chap 9 read by today

• Presentation today by Jonathan Rogers

• On Deck for Thursday Philip Crain, Gordon Chaney. Subject will be: Black flies, sand flies, biting midges and their diseases

• Read Chaps 10, 11, 12, 13

• Will review for hour exam on Thursday

• Note “In the News” on the website

Quiz Review• Question 1 – B, A, D. Note: Because of typo: E,A, D also was

acceptable. Grading – 2 out of 3 = full credit, 1 right = 1 point.

• Question 2. Grading – 4/5 = full credit, 2 or 3/5 = 1 pointX AllergiesX Psychological Stress__ Trench Fever & Relapsing FeverX Intermediate Hosts of Animal Parasites__ or X Food Contamination

• Question 3. Grading – 4/5 = full credit, 2 or 3/5 = 1 point.__ or X Lice are solenophages__ Bed bugs are laterally flattenedX All bugs are adapted to feeding on liquidsX Bed bugs are in the same order as Kissing Bugs__ Bed bugs are actually more closely related to lice than to Conenose bugs

Quiz Review

• Question 4. Best Answer in Class

“It is indirectly transmitted through the feces of the bug when the host scratches it into the biting wound or site or into mucus [sic] membranes.”

Class Quiz Scores

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Points Out of 10 Possible

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Disease pathology

• Pathogen replicates mainly within vascular endothelial cells.

• Infected cells proliferate and degenerate, results in vascular occlusion.

• Occlusion induces a focal ulcer followed by hematogenous dissemination of the pathogen systemically.

• Abrupt onset of clinical disease after ~4 weeks: headache, fever, and often a hemorrhagic rash.

• Ocular lesions sometimes occur as with all of the diseases produced by Rickettsiae.

Louse-borne Relapsing Fever

• Spirochete bacterium, Borrelia recurrentis

• Pathogen infects the louse blood stream, is transmitted when the louse is crushed & rubbed in to the skin.

• Few thousand/year, 95% of cases are in Ethiopia.

Trench Fever

• Bacterial disease, Bartonella quintana• A form of “Bartonellosis”. We’ll see

another one later.• Like typhus, transmitted in louse feces.• Often asymptomatic in healthy hosts. May

express nonspecifically in stressed hosts.• Increased association of stress & urban

environments leads to term: “Urban Trench Fever”.

Fleas• Order Siphonaptera with 15 families & about 2,500 spp.• All spp. are ectoparasites of vertebrates, almost all (94%)

target mammals.• Closest living relatives are the Boreidae (snow

scorpionflies) in the Order Mecoptera (scorpionflies)

Boreid example

“ctenidium” = “comb”, e.g. “genal comb” = “genal ctenidium”

“sensilium” =

“pygidium”

Flea Identification• Identification is based on external morphology• Usually difficult on “raw” specimens but easy on “cleared”

specimens• Several pictorial keys that are easy to use.• Here is a good one from CDC

Uncleared Specimen Cleared Specimen

Flea Identification: What is this flea?

Flea Identification: What is this flea?

Flea Identification: What is this flea?

Flea Identification: What is this flea?

Note the location of the ocular bristle

Flea Identification: What is this flea?

Medical/Public Health Significance

• Allergies• Tungiasis – infestation by chigoe fleas• Others (rickettsia, helminths, Q-fever, other

pathogens).• Murine (endemic) Typhus• Plague: 3 forms

– Bubonic is from the flea– Pneumonic from aerial dispersal– Septicemic from high-titer injection

Murine Typhus

• Also called “endemic typhus” or “flea-borne typhus”, see book for other names

• Rickettsial: Rickettsia typhii (different species than epidemic typhus, R. powazekii)

• Flea acquires pathogen from rats, passes it in feces, feces get scratched into skin.

• No obvious negative effect on flea (unlike R. powazekii which kills the louse).

• Patients present with mild – high fever, prostration, sometimes rash. Debilitation can be a couple of months, low fatality rate.

Plague

• Bacterial disease, Yersinia pestis

• Primarily a rodent pathogen, humans are accidental hosts

• When ingested, bacterium multiplies in flea gut, blocks it. Future attempts at feeding result in regurgitation of contaminated blood.

Manifestation• Following injection into the new host, initial replication is inside

tissue macrophages. • Macrophages rupture, releasing larger numbers of bacteria into the

blood stream.• Many attack the draining lymph nodes, which become hot, swollen,

tender, and hemorrhagic, giving rise to the characteristic black buboes responsible for the name of this disease.

• Within hours of the initial flea bite, the infection spills out into the bloodstream, leading to substantial involvement of the liver, spleen, and lungs.

• Patient develops a severe bacterial pneumonia, exhaling large numbers of viable organisms into the air during coughing fits representing a highly contagious health hazard to caregivers.

• Incubation period is 1 – 6 days (depending on form) and patient remains infectious for 3 weeks or death.

• Once infected/contaminated, most rodents & fleas remain infectious for life.

Spread of the Black Death

Historical Impact Example: The Horse Plague

Historical Impact Example: The Horse Plague

Historical Impact Example: The Horse Plague

Horse Plague Impact

• Spain ceased active colonization from Spain. Essentially froze Spanish influence.

• Italy never colonized the Americas• French colonial aspirations were restricted

in their infancy.• In the absence of competition from Spain,

Portugal, Italy, & France – England developed a blue-water navy.

Why the periodic pandemics?

• Three biotypes (“biovars”) of Y. pestis:– biovar ‘Antiqua’ – Justinian’s Plague (541)– biovar ‘Medievalis’ – Black Death (1347)– biovar ‘Orientalis’ – Chinese Plague (1894)

• At least some pandemics were more related to the vector than to the pathogen.– E.g. Horse Plague (1512) was probably driven

by the human flea, Pulex irritans rather than the Oriental Rat Flea, Xenopsylla cheopis

Current Status of Plague•Between 1998 and 2008, nearly 24,000 cases have been reported, including about 2,000 deaths

•In 2003, 9 countries reported 2118 cases and 182 deaths.

•98.7% of those cases and 98.9% of those deaths were reported from Africa.

•Most serious current epidemic is in the Congo (FKA Zaire).

• August, 2009, outbreak in Qinghai, China

US Human Cases

1970 - 1997

US normally has 10 – 20 cases/year