WILDLIFE DISEASESAND HUMANS

Robert G. McLeanChief, Vertebrate Ecology SectionMedical Entomology & Ecology BranchDivision of Vector-borne Infectious

DiseasesNational Center for Infectious DiseasesCenters for Disease Control and

PreventionFort Collins, Colorado 80522

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INTRODUCTION

Diseases of wildlife can cause signifi-cant illness and death to individualanimals and can significantly affectwildlife populations. Wildlife speciescan also serve as natural hosts for cer-tain diseases that affect humans (zoo-noses). The disease agents or parasitesthat cause these zoonotic diseases canbe contracted from wildlife directly bybites or contamination, or indirectlythrough the bite of arthropod vectorssuch as mosquitoes, ticks, fleas, andmites that have previously fed on aninfected animal. These zoonotic dis-eases are primarily diseases acquiredwithin a specific locality, and second-arily, diseases of occupation and avo-cation. Biologists, field assistants,hunters, and other individuals whowork directly with wildlife have an in-creased risk of acquiring these diseasesdirectly from animal hosts or their ec-toparasites. Plague, tularemia, andleptospirosis have been acquired in thehandling and skinning of rodents, rab-bits, and carnivores. Humans haveusually acquired diseases like Colo-rado tick fever, Rocky Mountain spot-ted fever, and Lyme disease becausethey have spent time in optimal habi-tats of disease vectors and hosts.Therefore, some general precautionsshould be taken to reduce risks ofexposure and prevent infection.

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GENERAL PRECAUTIONS

Use extreme caution when approach-ing or handling a wild animal thatlooks sick or abnormal to guardagainst those diseases contracteddirectly from wildlife. Procedures forbasic personal hygiene and cleanlinessof equipment are important for anyactivity but become a matter of majorhealth concern when handling animalsor their products that could be infectedwith disease agents. Some of theimportant precautions are:

1. Wear protective clothing, particu-larly disposable rubber or plasticgloves, when dissecting or skinningwild animals.

2. Scrub the work area, knives, othertools, and reusable gloves with soapor detergent followed by disinfec-tion with diluted household bleach.

3. Avoid eating and drinking whilehandling or skinning animals andwash hands thoroughly when fin-ished.

4. Safely dispose of carcasses and tis-sues as well as any contaminateddisposable items like plastic gloves.

5. Cook meat from wild game thor-oughly before eating.

6. Contact a physician if you becomesick following exposure to a wildanimal or its ectoparasites. Informthe physician of your possible expo-sure to a zoonotic disease.

EVENTION AND CONTROL OF WILDLIF

operative Extension Divisionstitute of Agriculture and Natural Resourcesniversity of Nebraska - Lincoln

nited States Department of Agricultureimal and Plant Health Inspection Serviceimal Damage Control

reat Plains Agricultural Councilildlife Committee

Precautions against acquiring fungaldiseases, especially histoplasmosis,should be taken when working inhigh-risk sites that contain contami-nated soil or accumulations of animalfeces; for example, under large birdroosts or in buildings or caves contain-ing bat colonies. Wear protectivemasks to reduce or prevent the inhala-tion of fungal spores.

Protection from vector-borne diseasesin high-risk areas involves personalmeasures such as using mosquito ortick repellents, wearing special cloth-ing, or simply tucking pant cuffs intosocks to increase the chance of findingcrawling ticks before they attach. Ad-ditional preventive methods includechecking your clothing and body andyour pets for ticks and removing theticks promptly after returning from in-fested sites. If possible, avoid tick-in-fested areas or locations with intensemosquito activity during the transmis-sion season. Reduce outdoor exposureto mosquitoes especially in earlyevening hours to diminish the risk ofinfection with mosquito-borne dis-eases.

Equally important preventive mea-sures are knowledge of the diseasespresent in the general area and the specific habitats and times of year thatpresent the greatest risk of exposure.Knowledge of and recognition of theearly symptoms of the diseases andthe conditions of exposure are essen-tial in preventing severe illness. Also

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Fig. 1. Reported human cases of wildlife rabies in the United States, 1991.

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important are medical evaluation andtreatment with proper antibiotics. Forexample, if you become ill followingsome field activity in a known plague-endemic area and you recognize theearly symptoms of the disease, seekingmedical care and informing the attend-ing physician of your possible expo-sure to plague will aid in the correcttreatment of your illness and reducethe risk of complications or evendeath.

In addition to taking personal precau-tions, risk of acquiring vector-bornediseases can be reduced in specificlocations through area-wide applica-tions of insecticides to control mos-quito or flea vectors or acaricides tocontrol tick vectors. Reduction in hostpopulations (for example, rodents) andtheir ectoparasites (fleas or ticks) maybe needed to control transmission ofsuch diseases as plague or Lyme

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disease. Vaccination of wildlife hostsas a means of reducing zoonotic dis-eases is currently being investigatedand may soon be available for diseaseslike rabies.

WILDLIFE DISEASESOF PUBLIC HEALTHCONCERN

Directly TransmittedDiseases

Rabies

Rabies is an acute disease, caused by avirus (rhabdovirus), that can infect allwarm-blooded animals, and is usuallyfatal. Certain carnivorous mammalsand bats are the usual animal hosts(Fig. 1; Table 1). Rabies occursthroughout most of the world; only

Australia and Antarctica are free of it.Most human cases have been con-tracted from rabies-infected dogs. Inthe United States, human cases havedecreased to an average of one personper year (75% of cases are acquiredoutside the United States). Reductionin human rabies is likely linked withthe intensive control of dog rabiesduring the 1950s and 1960s throughmassive vaccination campaigns, straydog control programs, and improve-ment in human treatment followingexposure. Nevertheless, thousands ofpeople in the United States continue toreceive treatment every year for pos-sible exposure to rabies virus by ani-mal bites. Most of the treatments arestill due to dog and cat bites; however,these pet species have the lowestoccurrence of reported rabies amongall animal species tested.

Rabies in wildlife increased dramati-cally during the 1960s and nowaccounts for most of the reported ani-mal rabies cases (91% in 1991). Some ofthe increase in reporting was due toreal increases in the number of cases,and some was due to an increasedawareness of wildlife rabies, particu-larly in striped skunks, raccoons, andbats. In 1991, 6,975 cases of animalrabies were reported in 49 states, theDistrict of Columbia, and Puerto Rico.Raccoons (44.2%), striped skunks(29.7%), and various species of bats(9.9%) continued to be the major hosts.Red and gray foxes (4.6%), other wild-life species (2.8%), and domestic ani-mals (8.9%) comprise the remainder ofhosts. During the last 2 years, raccoonsreplaced striped skunks as the majorwildlife host in the United Statesbecause of the continued expansion ofraccoon rabies in the northeasternUnited States. Animal cases arereported throughout the year,although the number of cases reportedreaches a seasonal peak for skunks inMarch and April, for raccoons inApril, and for bats in August.

Clinical Signs. Rabies is consideredalmost 100% fatal once clinical signsdevelop. The disease progresses rap-idly following the appearance of clini-cal signs, and the animal dies within afew days. Although abnormal behav-ior is not diagnostic for rabies (otherdiseases, like distemper, cause similarbehavioral changes), atypical behaviorand signs develop following braininfection, and rabies should be sus-pected whenever wild animals displayunusual behavior.

Infected animals usually display either“furious” or “dumb” rabies, althoughsome animals progress through bothstages. Skunks, raccoons, foxes, andother canids usually have furiousrabies and are unduly aggressivebefore convulsions and paralysis set in.Some animals, however, have dumbrabies and proceed to tremors andconvulsions without agitation oraggression. Other behavioral changesinclude friendliness or loss of fear,appearance in the daytime for sometypically nocturnal species (skunks,bats), unprovoked attacks on anything

that moves (including inanimateobjects), bewilderment, and aimlesswandering. Unusual barking, crying,and frothing at the mouth are addi-tional signs, which are the result ofparalysis of the throat muscles. Occa-sionally, rabid bats are encounteredprostrate or fluttering on the ground,unable to fly; they should be handledwith care because they can still biteand transmit rabies. Some rabid bats,particularly solitary species like thehoary bat, are aggressive and havebeen known to attack people. Indomestic animals, rabies should besuspected if there is any change in nor-mal habits, such as sudden change indisposition, failure to eat or drink, run-ning into objects, or paralysis.

Transmission. Rabies virus is trans-mitted primarily via the saliva duringthe bite of a rabid animal. However,other methods of transmission are pos-sible. Accidental exposure of woundsor cuts to the saliva or tissues of in-fected animals can occur. The virus isalso present in various body organs ofinfected animals, especially the brainand salivary glands, which poses ahealth hazard to persons who are fielddressing or performing necropsies onthese animals. In addition, aerosol ex-posure has occurred, although rarely,in caves containing very large popula-tions of infected bats. Transmissionbetween animals also occurs by inges-tion of infected tissues and by trans-placental passage to offspring.

When the virus enters the tissue of asusceptible animal or human, it multi-plies at the bite or inoculation site andtravels slowly up nerve fibers to thepart of the brain that controls the bit-ten area. The virus multiplies thereand spreads to other parts of the brainand eventually produces a variety ofsigns in the infected animal or person.The virus also spreads from the brainto other tissues, particularly to the sali-vary glands, where it multiplies and isreleased into the saliva. The virus isperpetuated in nature when an in-fected animal with virus in its salivabites another animal.

The virus is rarely present in the sali-vary glands without first occurring inthe brain and is present in the saliva

for only a few days before clinicalsigns appear. Exceptions occur in afew species of bats and in a unique Af-rican virus strain found in dogs. Thelength of the incubation period (fromthe time the animal is bitten until clini-cal rabies appears) is usually 2 to 3weeks, but varies from 10 days toseveral months.

Handling of Suspect Animals andDiagnosis. Use caution whenapproaching a suspected rabid animalsince many are still aggressive and canbite even if paralyzed. If the animal isstill alive, it should be killed humanelywithout damaging the head. To con-firm whether an animal is infectedwith rabies, the animal must be sub-mitted to the local health departmentor state diagnostic laboratory fortesting.

Avoid exposure to any sick or deadanimals that are suspected to haverabies. Handle any dead animal withgloves or with a plastic bag that can beturned inside-out to cover and containthe animal. Avoid direct skin contactwith the animal. For large animalssuch as skunks and raccoons, removethe head cautiously and seal it in aplastic bag, avoiding contact or aerosolexposure. Seal the whole animal orhead inside an additional plastic bag(double) and keep it cool at all times.Do not freeze the specimen unless adelay of several days is anticipatedbefore it is examined for rabies. Disin-fect gloves or knives that were in con-tact with the animal with a strongdetergent or bleach or dispose of them.

For transport to the laboratory, placethe double-wrapped specimen in aleak-proof container with a coolant(not wet ice). Send the container bybus or other prearranged transporta-tion. Include information about thespecimen (species, date, geographicdata, behavior) and the names,addresses, and telephone numbers ofthe person submitting the specimenand of anyone exposed to the animal.

To test for rabies, a fluorescent anti-body (FA) test is performed directly onbrain tissue to distinguish rabies virusfrom other disease agents (like distem-per virus) that could be present in theanimal’s brain. In some states, brain

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material is inoculated into mice todemonstrate virus for those specimensthat resulted in human exposure.

If a person or pet is exposed to an ani-mal suspected of having rabies butthat has not been captured, record adescription of the suspect animal (spe-cies, behavior) and provide thedescription to public health officials orthe attending physician to determinepossible treatment.

Prevention and Treatment. Thebest treatment for rabies is prevention.Individuals at high risk of exposure torabies, such as wildlife biologists,game wardens, animal control officers,animal handlers, and veterinariansshould be vaccinated before potentialexposure. Safe and highly effectivevaccines are available through a physi-cian or the local health department.

First aid should immediately be pro-vided to a person who has been bittenby or had contact with a potentiallyrabid animal. Scrub the exposed site,including bite wounds, with soap andwater or water alone and flush thor-oughly. Then apply a strong first aidsolution (iodine) or cream. First aidtreatment is the most effective methodof preventing infection by the rabiesvirus but should not preclude medicalattention from a physician, hospitalemergency room, or the local healthdepartment. Contact your physician orhealth department as soon as possibleto determine dosage of rabies vaccineand whether antirabies serum isrequired. Inform the health care pro-fessionals about the rabid animal andthe circumstances of the exposure(species of animal involved and itsbehavior, if the attack or bite from theanimal was provoked, and what typeof first aid was administered).

Hantavirus

Hantavirus includes a group of virusesthat can cause a febrile illness in hu-mans which can be accompanied bykidney, blood, or respiratory ailmentsand can sometimes be fatal. The febrileillness includes fever, headache,muscle aches, nausea, vomiting, andlower back pain. Field and commensal

rodents are the natural reservoirs forviruses in this group and these virusesare found worldwide. Infected rodentsshed virus in their urine, feces, and/orsaliva and can remain chronicallyinfected. The contaminated excretafrom infected rodents are thought tobe the source of virus for aerosol anddirect (animal bite) transmission toother rodents and humans.

The recent discovery of a possible newhantavirus in the southwestern UnitedStates and its apparent increased viru-lence, has heightened the awareness ofand concern for rodent-associated dis-eases. It produces produces respira-tory distress and potential death inhumans. Human cases and deathsfrom this viral infection were firstreported in 1993 in the Four Cornersarea of Arizona, Colorado, NewMexico, and Utah and, more recently,throughout the United States. Prelim-inary information has incriminated thedeer mouse (Peromyscus maniculatus)as the natural reservoir and source ofhuman infection in that region. Indi-viduals trapping and handling smallrodents in this region should takeincreased precautions to reduce theirexposure to this virus. They should atleast wear surgical gloves and maskswhen processing rodents (contactCDC Hotline for more detailed andthorough safety information). Rodentcontrol with careful handling and dis-posal of carcasses should be institutedat campsites or in cabins before theyare occupied. The premises should besprayed with detergents or dilutedbleach before thorough cleaning. Wet-mopping is recommended. Drysweeping and vacuuming mayincrease risk of producing airborneparticles. Rodent harborage should beremoved from premises and from thesurrounding area. Exclude rodentswhere possible.

Trichinosis

Trichinosis may result in diahrrea,sudden edema of the upper eyelids,photophobia, muscle soreness andpain, skin lesions, thirst, sweating,chills, and weakness. Other respiratory

and neurological symptoms mayappear if treatment is delayed.

Trichinosis is contracted by eatinginfected meat which contains theencysted parasites. The parasites mayremain infectious in meat which is rawor poorly cooked.

Trichinosis is caused by a nematodeparasite which produces the disease inhumans and domestic and wild ani-mals. Evidence indicates that nearly allmammals are susceptible to infectionswith this parasite, which encysts in themuscle of the host and is then trans-mitted through consumption ofinfected flesh. As would be expected,the disease is most common in wildcarnivores and scavengers.

As with other wildlife diseases,trichinosis is difficult to control innature. However, certain steps can betaken to decrease the problem. Car-casses of carnivores and other meat-eating species should not be discardedin the fields or woods, but should bemade unavailable by burying or othermeans. These carcasses also should notbe fed to swine, dogs, or other domes-tic animals. Open garbage dumpsshould be replaced by the landfill typeor other methods of disposal wherewildlife will not have access to meatscraps. If open garbage dumps cannotbe eliminated, rodent control pro-grams should be initiated and theareas fenced to prevent scavenging bylarger animals such as foxes. Thesesteps would markedly reduce theproblem of trichinosis in wildlife in theUnited States.

If carnivorous or omnivorous wildlifesuch as bears, bobcats, opossums,raccoons, or feral pigs are consumedby humans, the meat should beproperly prepared by cooking,freezing, or curing to destroy anyviable trichinae. Cooking to an internaltemperature of 137oF is deemedsufficient for pork, while freezing at5oF for 20 days, -10oF for 10 days, or -20oF for 6 days will kill trichinae.Curing should follow approvedgovernment regulations.

Mosquito-borneEncephalitis

Encephalitis is a disease caused bymosquito-borne viruses (arboviruses)that affect the central nervous system.Infections range from unapparent tomild, nonspecific illnesses (fever, head-ache, musculoskeletal pain, and mal-aise) to occasionally severe illness ofthe central nervous system resulting inpermanent neurologic damage andpossibly death. The four major types ofencephalitis in the United Statesinclude St. Louis encephalitis (SLE),California encephalitis (CE primarilyincludes the LaCrosse virus [LAC]),eastern equine encephalitis (EEE), andwestern equine encephalitis (WEE).The distribution of these arbovirusesvaries (Fig. 2). SLE occurs throughoutthe United States (an epidemic oc-curred in central Florida in 1990 andArkansas in 1991), WEE occurs west of

Fig. 2. Distribution of mosquito-borne encephalitis i(c) eastern equine encephalitis (EEE); and (d) wester

EEE

SLE

the Mississippi River, EEE occurs eastof the Mississippi River but mostlyalong the Atlantic and Gulf coasts andnorth-central states, and CE occurs inCalifornia and the eastern UnitedStates (LAC type). Human cases ofarbovirus infection have a seasonaloccurrence from mid- to late summer.

These distinct viruses naturally infect avariety of birds and mammals and aretransmitted between animals by mos-quito vectors. Occasionally, infectedmosquitoes will feed on human orequine hosts that are “dead ends” forthe viruses, with little or no chance ofsubsequent transmission to other mos-quitoes. These viral infections may,however, result in severe illness ordeath in humans or horses (EEE andWEE). Only EEE and occasionallyWEE viruses adversely affect wild ver-tebrates; for example, EEE causesdeath in ring-necked pheasants and

n the United States, 1964 to 1992; (a) St. Louis encepn equine encephalitis (WEE).

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other exotic game birds, house spar-rows, red-winged blackbirds, whoop-ing cranes, and other species. Thewildlife hosts for LAC virus are theeastern chipmunk, tree squirrels, andfoxes. The natural hosts for the otherthree viruses are mostly songbirds,although squirrels and jackrabbits maybe involved in WEE transmission.

No treatment or commercial vaccine isavailable for humans, but vaccines forWEE and EEE are readily available forhorses. The best preventive measuresare personal protection against mos-quito bites, especially avoiding expo-sure to mosquitoes during earlyevening hours, and the use of repellents.Mosquito populations can be reducedin an area by eliminating breeding sitesfor vector species. Killing adult mos-quitoes with areawide applications ofinsecticides has been most effective inpreventing epidemics.

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halitis (SLE); (b) California encephalitis (CE);

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Fig. 3. Distribution of Colorado tick fever (human cases) in the United States, 1980 to 1988. (Solid line outlines distribution of Dermacentor andersoni.)

Tick-borne Diseases

Colorado Tick Fever

Colorado tick fever (CTF) is an acuteand rather benign disease caused by avirus (coltivirus) that is transmitted tohumans by ticks. Symptoms are usu-ally limited to high fever, headache,muscle aches, and lethargy, but thesymptoms are frequently biphasic andrecurring. The disease is confined tothe mountains or highland regions ofeight western states and westernCanada (Fig. 3). About 150 to 200 casesare reported each year; 1,438 caseswere reported from 1980 to 1988 ineight western states, 63% of them inColorado. CTF is transmitted tohumans during the spring and earlysummer by the bite of the adult stage

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of the Rocky Mountain wood tick(Dermacentor andersoni) or by D.occidentalis in California. The virus ismaintained in nature through trans-mission by immature stages of ticks tovarious species of small mammals,particularly chipmunks, ground squir-rels, and deer mice during the springand summer months. The virus sur-vives the winter in infected ticknymphs and adults. The habitats thatsupport the rodent hosts and tick vec-tors of the virus in the disease endemicregion contain rocky surfaces withmoderate shrub cover and scatteredpines.

Avoid tick-infested habitats duringspring and early summer and use per-sonal protection against ticks. No vac-cines or treatment are available.

Rocky Mountain Spotted Fever(Tick-borne Typhus)

Rocky Mountain spotted fever (RMSF)is a moderate to severe illness causedby a rickettsia (Rickettsia rickettsii). Thedisease is distinguished by a suddenonset of high fever, severe headache,muscle pain, and a red rash starting onthe extremities about 3 to 6 days afteronset of symptoms and extending tothe palms of hands and soles of feetand then to the rest of the body. Delir-ium, coma, and death occur in about1% to 2% of cases (15% to 20% inuntreated cases). The disease is trans-mitted to humans in the United Statesby several hard tick (Ixodidae) species;D. andersoni in the Rocky Mountainregion, D. variabilis in the east andsoutheast, and Amblyomma americanum

in the south-central states. In 1990, 649cases of RMSF were reported from allregions of the United States, althoughmore cases were reported in the south-Atlantic and south-central states (Fig.4). The natural hosts for the rickettsiaare a variety of wild rodents, althoughrabbits and wild and domestic carni-vores are involved in some cases. Therickettsia survive the winter months inthe tick vector and may be maintainedby transovarial transmission from thefemale adult tick to its offspring.

Avoid tick-infested areas and use per-sonal measures to protect against tickbites. No vaccine is presently licensedfor public use, but antibiotic treatmentis effective and should be initiatedwithout waiting for laboratory confir-mation of clinical diagnosis.

Fig. 4. Distribution of Rocky Mountain spotted fev

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Lyme Disease

Lyme disease is caused by a spirochetebacterium (Borrelia burgdorferi) that istransmitted to humans by hard ticks.Early symptoms include a flu-like ill-ness with headache, slight fever, mus-cle or joint pain, neck stiffness, swollenglands, jaw discomfort, and inflamma-tion of the eye membranes. A diagnos-tic rash, erythema migrans (EM),occurs in 65% to 75% of the cases. Therapidly expanding red rash starts atthe tick bite site and expands to anearly circular lesion of about 1 to 8inches (2 to 20 cm). It often has a bulls-eye appearance with central clearingand/or darkening around the edge.Additional smaller skin lesions mayappear at other sites of the body andmay last for days or weeks. Later

er (human cases) in the United States, 1990.

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symptoms, including heart, nervoussystem, and joint manifestations, maydevelop in untreated individuals. Thejoint pain and swelling usually occurone or more months after infection,may involve one or more joints, andmay recur in different joints; the kneejoint is most frequently affected. Do-mestic animals may be affected aswell.

In 1992, 9,695 cases of Lyme diseasewere reported in 44 states (Fig. 5).Most cases were reported in the north-eastern and upper midwestern stateswhere the vector is the deer tick (Ixodesscapularis) and where transmission ispredominately in residential commu-nities. Other vectors are I. pacificus onthe West Coast and possibly A.americanum in the Southeast and in

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south-central states. Transmission inthese other regions of the United Statesmay be more sporadic and occur dur-ing outdoor activities related to recre-ation and occupation. Acquisition ofLyme disease by humans peaks duringthe summer months when the ticknymphs are feeding on hosts. Becauseof its small size, the attached nymphfrequently goes unnoticed and is notremoved. The transmission cycle ofLyme disease begins when larvaeacquire spirochetes while feeding oninfected white-footed mice, chip-munks, other rodents, and birds.Engorged larvae drop to the ground,molt to the nymphal stage, and waituntil the following summer to attach toand transmit spirochetes to susceptiblerodents, birds, larger mammals, andhumans. Uninfected larvae subse-quently feed on these wild vertebratehosts to complete the transmission

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cycle. The engorged nymphs drop tothe ground and molt into adult tickswhich are active during the fall andfollowing spring and feed on largemammals, primarily deer. Deciduousforest is the predominant habitat forthe tick vector and vertebrate hosts inthe Northeast and Midwest. Otherprime habitats include forested areasinterspersed with residential develop-ment and grass and shrub areas, par-ticularly along forest edges.

Patients treated with appropriate anti-biotics during the early stages of thedisease usually have rapid and com-plete recovery. Even patients treatedduring later stages generally respondwell and recover. No vaccine is avail-able except for domestic dogs. Avoidlocations with ticks during seasonalactivity periods, use personal mea-sures to protect against ticks, become

knowledgeable about the symptoms ofLyme disease, and seek medical careand treatment if infected.

Tularemia

Tularemia is caused by the bacteriaFrancisella tularensis and is character-ized by sudden onset of high fever andchills, joint and muscle pain, and pros-tration. Slow-healing sores or lesionsdevelop at the site of entry of the bac-teria (or arthropod bite). Inflammationand swelling of nearby lymph nodesfollow.

Tularemia is endemic throughoutNorth America (Fig. 6). Most of the100 to 300 cases reported each year arefrom the area between the RockyMountains and the Mississippi River(especially Arkansas and Missouri).Most cases are acquired during thesummer months from vector transmis-

sion; however, a second peak of casesoccurs during the winter and is prob-ably associated with rabbit huntingand carnivore trapping.

The bacteria is maintained in rabbits,hares, rodents, and birds by tick trans-mission. The natural reservoir for thebacteria includes infected ticks andanimal species that are less susceptibleand thus survive acute infections.Hard ticks, primarily D. andersoni, D.variabilis, and Haemaphysalis leporis-palustris, and some flies, especially thedeerfly (Chrysops discalis), can subse-quently transmit the disease tohumans. Tularemia can also be trans-mitted directly to humans. Transmis-sion routes include drinking contami-nated water; eating contaminated foodor improperly cooked game meat;inhaling aerosols contaminated withrodent urine, feces, or dust; cuts fromcontaminated knives or other instru-

Fig. 6. Distribution of tularemia (human cases) in th

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ments; and scratches or bites frominfected animals. Use personal protec-tion measures against ticks and prac-tice good sanitation procedures whenhandling wild animals, especially rab-bits. Promptly seek medical care andtreatment if symptoms develop.

Relapsing Fever

Relapsing fever can be caused by sev-eral Borrelia spirochete bacteria, whichare related to the Lyme disease spiro-chete and are transmitted by soft ticks(Argasidae). Symptoms resembleLyme disease except for the absence ofthe diagnostic rash and the presence ofrecurring fever. The most commontype is caused by B. hermsii. Most hu-man cases of this type of relapsingfever have been associated with logcabins or houses containing rodentnests (particularly of chipmunks andpine squirrels) and Ornithodoros hermsi

e United States, 1991 (191 cases reported).

ticks. This species of tick is active atnight. Since it feeds rapidly and its biteis relatively painless, it may go unno-ticed. The ticks feed on humans whenthe rodents disappear from the cabinnests because of rodent control mea-sures or death from other diseases.Most human cases occur during thesummer months when the cabins arein use. Sporadic cases are reported pri-marily in the mountainous regions ofthe western United States and BritishColumbia; 159 cases were reportedduring 1985 to 1991 in 10 westernstates (Fig. 7). Two outbreaks occurredamong tourists and staff staying incabins at the Grand Canyon in Arizonain 1973 and 1990. Inspect cabins for ro-dent use and nests, promptly removenests, and treat cabins with insecti-cides or fumigate to kill any remainingticks. Rodent-proof cabins to preventrodent entry.

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Fig. 7. Distribution of relapsing fever (human cases) in the United States, 1985 to 1991.

Two other species of relapsing feverspirochetes are transmitted occasion-ally to humans in the western UnitedStates by Ornithodoros ticks. The spiro-chete B. parkeri is transmitted by O.parkeri, mostly in California, and B.turicatae by the tick O. turicata. Fivehumans were infected with B. turicataein Texas in 1990 following explorationof a cave containing infected ticks. Forprevention, use personal protectionagainst tick exposure. If sick withrelapsing fever, seek medical care andappropriate antibiotic treatment.

Other Tick-borne Diseases

Three other tick-borne diseases occurin the United States. Human ehrlichio-sis is a recently recognized diseasecaused by a rickettsia, Ehrlichia chaf-feensis. It is probably transmitted byticks. Symptoms are similar to those ofRMSF: an acute fever with headache,muscle ache, and nausea. A rash

appears less frequently and for a muchshorter duration. From 1986 to 1991,262 cases and 4 fatalities were reportedin 23 states, the majority occurring inMissouri and Oklahoma. Use personalprotection against ticks and seek medi-cal care and treatment if sick.

Powassan encephalitis is caused by avirus (flavivirus) which is transmittedby the ticks I. cookei, D. andersoni, andother Ixodes spp. Symptoms includethe sudden onset of fever, sore throat,sleepiness, headache, and disorienta-tion. Encephalitis, meningitis, and,occasionally, partial paralysis maydevelop. Natural hosts are marmots,sciurid rodents, rabbits, hares, carni-vores, and possibly birds. Only 19cases have been reported, all in NewYork, Pennsylvania, Ontario, and Que-bec. Use personal protection to reduceexposure to ticks. No treatment isavailable.

Babesiosis is a protozoan disease withgradual onset of fever, sweating, lossof appetite, fatigue, general muscleache, and possibly prolonged anemia.The disease can be severe and some-times fatal. A protozoan, Babesiamicroti, is transmitted among wildrodents, particularly white-footedmice, by the tick I. scapularis along thecoastal areas of New England and onadjacent offshore islands. This tickmay be infected occasionally with bothB. microti and the Lyme disease spiro-chete. Use personal protection mea-sures to prevent tick exposure andseek medical care if sick.

Personal Protection

The following personal measures canprotect against tick-transmitteddiseases:

1. When possible, avoid tick-infestedareas.

2. To better see crawling ticks, tuckpant legs into socks and tape thetops of socks over pant legs. Wearlight-colored clothes.

3. Use tick repellent on exposed skin(DEET) or treat clothes withpermethrin. Follow label instruc-tions for use.

4. Check yourself frequently for ticksand remove them.

5. After outdoor activity, remove andwash field clothing promptly anddry clothes at a high temperature.

6. Inspect your body carefully andremove attached ticks with apointed tweezers. Grasp ticks asclose to the skin as possible and pullthem loose with a slow, steadymotion.

7. Inspect pets carefully for ticks andremove ticks soon after returningfrom the outdoors.

Fig. 8. Distribution of plague (human cases) in the U

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Flea-borne Diseases

Plague

Plague is an acute disease caused bythe bacteria Yersinia pestis. Humansusually become infected by the bites ofinfected fleas but also directly fromexposure to tissues or body fluidsfrom diseased animals, especiallywhen skinning animals. The disease ischaracterized by the sudden onset offever and chills, followed by the devel-opment of swollen and painful lymphnodes (buboes) in the armpits, groin,and other areas 2 to 6 days followingexposure. In addition to the bubonicform, septicemic infection maydevelop and involve other organs.Secondary infection of the lungs maylead to primary plague pneumonia,which then can be transmitted fromperson to person by aerosol. The dis-ease may be only mild and short-livedbut frequently progresses to a severe

nited States, 1970 to 1990.

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form, with 25% to 60% fatality inuntreated cases. In the United States,plague is maintained in wild rodentpopulations in the western states byflea transmission between rodents. Syl-vatic plague may persist in these ani-mal populations with varying severity,depending on the species’ resistance.Prairie dogs are susceptible to suddendie-offs. Outbreaks of plague havedecimated prairie dog colonies in lessthan 1 to 2 years. Rabbits, hares, carni-vores, and wild ungulates have alsobeen infected occasionally. Humancases of plague are reported most fre-quently in New Mexico, Arizona, Cali-fornia, Colorado, and Oregon (Fig. 8).More than 50% of the 284 cases in theUnited States reported from 1970 to1990 were in New Mexico. Use insectrepellents on skin or treat field clotheswith permethrin. Practice good sanita-tion procedures when handling ani-mals. Seek medical care and treatmentif sick.

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Murine Typhus Fever

Murine typhus fever is caused by Rick-ettsia typhi, a rickettsial organism thatoccurs throughout the southeasternand Gulf Coast states and southernCalifornia. Rats are the reservoir ani-mals from which the disease reachesmany humans by way of rat fleas. Theoriental rat flea, Xenopsylla cheopis, isconsidered the most important vectorof the disease. The causative organismenters the bloodstream when feces ofinfected fleas are scratched or rubbedinto a flea-bite wound or other breaksin the skin. Murine typhus is similar toepidemic or louse-borne typhus, butillness is much milder and the fatalityrate in untreated cases is much lower.

Commensal Rodent-borneDiseases

Rats and mice are responsible for thespread of over 35 diseases, eitherdirectly, through contamination ofhuman food with their urine or feces,or indirectly, by way of rodent fleasand mites. Following are brief descrip-tions of the more common of thesediseases.

Rat-bite Fever

Rat-bite fever is caused by the bacteriaStreptobacillus moniliformis, which isfound on the teeth and gums of rats. Itis transferred from rats to humans bythe bite of the rat. The most frequentlyoccurring rat-bite fever in the UnitedStates is called Haverhill fever. It issimilar to the rat-bite fever of theOrient called sodoku (caused bySpirillus minus).

Leptospirosis (Weil’s Disease)

Leptospirosis is a mild to severe infec-tion that is seldom fatal. Human casesof the disease result from direct orindirect contact with infected urine ofrodents and other animals. The spiro-chetes (Leptospira spp., primarily L.icterohemorrhagiae) are found in con-taminated water or on food, and mayenter humans through mucous mem-branes or minute cuts or abrasions ofthe skin. Thus, Weil’s disease is oftenfound in sailors, miners, sewer work-

ers, and fish or poultry dealers. In arecent study in Hawaii, Norway rats,roof rats, and house mice were foundto have high L. icterohemorrhagiaecarrier rates.

Symptoms of leptospirosis infectionrange from none to severe, with acutefatalities. Many infections are charac-terized by diarrhea, chills, vomiting,myalgia, and kidney damage. Preven-tion is the most important means ofdealing with this disease. Proper sani-tation, rodent-proofing, and food stor-age and handling are essential.Medical attention is typically required.

Salmonellosis

The Salmonella group of bacteria existsnearly everywhere in the environmentand, unfortunately, several serotypesare pathogenic to humans and otheranimals. Salmonellosis can lead tosevere cases of gastroenteritis (foodpoisoning), enteric fever septicemia(blood poisoning), and death. Foodpoisoning, the most common malady,is characterized by a sudden onset ofabdominal pain, diahrrea, nausea, andvomiting. Due to the severity of thisdisease, medical attention is typicallyrequired.

Salmonella bacteria recognize few hostbarriers and are transmitted in manyways. One common form of transmis-sion is through food contaminated byrat or mouse feces that contain Salmo-nella (especially S. typhimurium) organ-isms. It may also be spread by birds,which contaminate food with theirfeces or bacteria carried on their feet.

As with leptospirosis, the most impor-tant means of reducing the potential ofthis disease is through proper sanita-tion, rodent-proofing, and food storageand handling. Rodent control throughtrapping and appropriate use of toxi-cants may also be necessary.

Rickettsialpox

Rickettsialpox is a mild nonfatal dis-ease resembling chicken pox. It iscaused by a rickettsia (Rickettsia akari),which is transmitted from house miceto humans by the bite of an infectedhouse mouse mite (Liponyssoides

sanguineus). In this country rickettsial-pox has been reported in Boston, WestHartford, New York, Cleveland, andPhiladelphia.

Bird-borne Diseases

Large roosting concentrations of birdscan be noisy, and the associated drop-pings can be a nuisance because of theobjectionable odor and mess. In addi-tion, birds may carry and transmitdiseases to livestock and humans. Col-lections of droppings may provide amedium for bacterial and fungalgrowth that could pose a potentialpublic health problem. Birds should bedispersed or controlled when theyform large concentrations near humanhabitations and are judged to pose athreat to public health or livestock.Concentrations of birds that do notthreaten human health or agricultureare usually better left undisturbed.

Histoplasmosis

Histoplasmosis is a respiratory diseasein humans caused by inhaling sporesfrom the fungus Histoplasma capsula-tum. Birds do not spread the diseasedirectly — spores are spread by thewind and the disease is contracted byinhalation. Bird droppings enrich thesoil and promote growth of the fun-gus. Notable sources for histoplasmo-sis infection include: (1) traditionalbird roosts, (2) poultry farms, (3)enclosed buildings where birds or batshave roosted, and (4) natural ororganic fertilizers. In addition, the fun-gus can grow in various natural soils,with or without droppings. In someareas, such as the Ohio Valley, histo-plasmosis is so widespread that 95% ofthe human population becomesinfected, whether associated withbirds or not.

Infection by only a few spores gener-ally produces a mild case in humansand people are often unaware thatthey have contracted the disease(unless it is detected later through askin reactivity test or lung X ray thatreveals healed lesions). A more severeinfection may result in an acute respi-ratory illness with flu-like symptoms

(in fact, histoplasmosis is often misdi-agnosed as flu). The most seriousinfections, usually resulting from mas-sive spore inhalation, may involve adissemination of the fungus throughthe blood stream. Such cases maybecome chronic, recurring at latertimes, and affect organs other than thelungs. Treatment with an antifungalagent such as amphotericin B or imi-dazole ketoconazole may be pre-scribed in more severe cases.

Not all blackbird or starling roostspose immediate public health prob-lems related to histoplasmosis. Thehistoplasmosis fungus grows readilyin the soil beneath bird roosts, but itcannot form spores under the acidicconditions of fresh droppings. Anactive, undisturbed roost may onlygive off a few spores. Old or aban-doned roosts, however, can pose a sig-nificant threat to human health. Afterthe droppings have dried out or beenleached by the rain, the right condi-tions develop for spore release. If thesoil is stirred up under dusty condi-tions, as may be the case in land clear-ing or bulldozing, massive amounts ofspores may be released. Severe epi-demics have occurred in associationwith bird roosts under such condi-tions.

Birds in large roosts can be dispersedby the use of various frighteningdevices or by roost thinning or clearing(see Bird Dispersal Techniques). Pre-cautions should be taken when work-ing around an old or abandoned roostsite. It is wise to test for the presence ofhistoplasmosis before beginning anywork. Wear a self-contained breathingapparatus or face mask with a dust fil-ter (less than 2 microns) to prevent in-halation of the spores. Wear protectiveclothing, gloves, and boots that can beremoved and disinfected with forma-lin and washed. If an area that wasonce a bird roost is going to be clearedor bulldozed, the area should bedampened with water or work shouldbe done when the weather is wet orcold or both. Avoid working underdry, dusty conditions in late summer.A roost may be decontaminated byspraying it with a 3% to 5% solution of

formaldehyde before clearing, but thisoption is very expensive.

Ornithosis (Chlamydia psittaci,psittacosis)

Ornithosis is an infectious respiratorydisease caused by Chlamydia psittaci, aviruslike organism that affectshumans, pets, and livestock. It usuallyleads to a mild pneumonia- or flu-likeinfection, but it can be a rapidly fataldisease (less than 1% of the casesreported in the United States). Inhumans many cases occur that areundetected or incorrectly diagnosed.Pigeons are most commonly associ-ated with the transmission of orni-thosis to humans. Birds have adaptedto the disease and show no symptoms,but act as healthy carriers, sheddingthe organism in their feces, which latermay become airborne as dust. The dis-ease may also be contracted from para-keets, farm poultry, or waterfowl.

People working in dry, dusty areaswhere bird droppings are present,should wear face masks or respiratorsto avoid inhaling airborne avian fecalmaterial. Spray work areas with waterand/or disinfectants to minimize thepotential for airborne infections par-ticles. Medical attention, includingantibiotic treatments are recom-mended for disease treatment.

Salmonellosis

The Salmonella group of bacteria canalso be transmitted by birds. Refer toCommensal Rodent-borne Diseases(above) for additional information.

Other Bird-borne Diseases

Pigeons, starlings, sparrows, black-birds, and other types of birds havebeen implicated in the transmission ofvarious diseases of significance tohumans or livestock. Starlings havebeen shown to be vectors of transmis-sible gastroenteritis (TGE) of swine.The virus can be carried in an infectivestate in the birds’ intestines or on theirfeet for up to 30 hours. It is generallyfatal to baby pigs and causes weightloss in adults. Starlings may also beinvolved in the transmission of hogcholera. Cryptococcosis is a fungal

disease spread by pigeons andstarlings that results in chronic, usuallyfatal, meningitis. Various species ofbirds may also play a part in thetransmission of encephalitis,Newcastle disease, aspergillosis,toxoplasmosis, pseudotuberculosis,avian tuberculosis, and coccidiosis.

Conclusion

Wildlife workers tend to ignore therisks associated with handling wildlifespecies and working in natural envi-ronments. Diseases of wildlife ordiseases present in their habitats caninfect humans and some can causeserious illness or even death. Becom-ing aware of the potential diseasespresent and taking precautions todecrease exposure will greatly reducechances of becoming infected with oneof these diseases. This section providesa description of the major zoonoticdiseases of wildlife in the United Statesthat can also infect humans and givesinformation on disease prevention.Other diseases are briefly listed inTable 1 or can be found in one of theselected references.

You can prevent infection with zoo-notic diseases and reduce the serious-ness of an illness by observing thefollowing recommendations:

1. Become aware of which zoonoticdiseases are present in your areaand their clinical symptoms.

2. Obtain any preexposure vaccina-tions that are available, particularlyfor rabies.

3. Take personal precautions to reduceexposure to disease agents andvectors such as ticks, mosquitoes,and fleas.

4. Practice good sanitation procedureswhen handling or processinganimals or their products.

5. If you become ill, promptly seekproper medical treatment andinform the physician about possibleexposures.

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Acknowledgments

Portions of this chapter were derived from F. R.Henderson. 1983. Wildlife diseases and man.in R. M. Timm, Prevention and Control ofWildlife Damage. Univ. Nebraska Coop. Ext.Lincoln.

For AdditionalInformation

For further information, consult the local orstate health department or contact the CDCVoice Information System, Centers for DiseaseControl and Prevention, Atlanta, Georgia, at(404) 332-4555.

Acha, P. N., and B. Szyfres. 1987. Zoonoses andcommunicable diseases common to man andanimals, 2d ed. Pan Am. Health Org.Washington, DC. 963 pp.

Adrian, W. J., ed. 1981. Manual of commonwildlife diseases in Colorado. Colorado Div.Wildl. Denver. 139 pp.

Benenson, A. S., ed. 1990. Control ofcommunicable diseases in man, 15th ed. Am.Public Health Assoc. Washington, DC.532 pp.

Thorne, E. T., N. Kingston, W. R. Jolley, and R. C.Bergstrom eds. 1982. Diseases of wildlife inWyoming, 2d ed. Wyoming Game Fish Dep.Cheyenne. 353 pp.

Weeks, R. J., and A. R. Stickley, Jr. 1984.Histoplasmosis and its relation to birdroosts: a review. Denver Wildl. Res. Center.Bird Damage Res. Rep. No. 330. Denver,Colorado. 23 pp.

EditorsScott E. HygnstromRobert M. TimmGary E. Larson

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Table 1. Some important wildlife diseases that affect humans.

Disease Parasite Method of Wildlife Type of Human(Agent) Transmission Hosts Illness

Direct

Rabies Virus Animal bite, Striped skunk, raccoon, Paralysis, convulsions,(rhabdovirus) aerosol foxes, bats, and other coma, death

mammals

Hantavirus Virus Aerosol, Deer mice, other Fever, headache, muscle(hantavirus) animal bite wild and commensal aches, nausea, vomiting,

rodents back pain, respiratorysyndrome

Leptospirosis Bacteria Urine contamination, Commensal and wild Fever; jaundice; neuro-(Leptospira spp.; ingestion rodents, rabbits, fox, logic; pain in abdomen,icterohemorrhagiae) skunk, raccoon, joints, or muscles;

opossum, deer nausea; may be fatal

Brucellosis Bacteria Contamination, Hoofed animals Intermittent fever, chills,(Brucella spp.; ingestion (coyote) headache, body aches,abortus) (milk, etc.) weakness, weight loss

Rat-bite fever Bacteria Rodent bite Commensal rodents Abrupt onset with chills(Streptobacillus and fever, headache,moniliformis) muscle ache, followed

by rash on legs andarms, arthritis

Salmonellosis Bacteria Ingestion of bacteria Rodents, swine, cattle, Sudden onset of head-(Salmonella spp.) in food contaminated wild birds, poultry, ache, fever, abdominal

with feces pet turtles pain, nausea, diarrhea,vomiting

Ornithosis Chlamydia Inhalation of Parrot and sparrow- Fever, chills, headache,(Psittacosis) (Chlamydia contaminated air like birds, pigeons, muscle pain, loss of

psittaci) waterfowl, domestic appetite, sweating,birds pneumonia

Histoplasmosis Fungus Inhalation of None, grows in soil Mild fever and(Histoplasma spores enriched by feces influenza-like illness,capsulatum) under bird and bat pneumonia, hepatitis,

roosts endocarditis, death

Cryptococcosis Fungus Inhalation None, grows in Meningitis; lung, liver,(Cryptococcus is suspected droppings in and bone infection; skinneoformans) pigeon nests lesions or ulcers

Trichinosis Nematode worm Ingestion of uncooked Swine, bear, wild and Nonspecific gastroenter-(Trichinella spiralis) meat containing larval domestic carnivores, itis, loss of appetite,

cysts wild and domestic nausea, diarrhea, swollenrodents eyelids, fever, chills,

muscle aches

Ascarid Nematode Ingestion of nematode Raccoon Larval stage invades androundworm (Baylisascaris eggs (raccoon feces damages body organs,

procyonis) contamination) including brain

Direct and Indirect

Plague Bacteria Contamination from Wild rodents (prairie Fever, headache, severe(Yersinia pestis) skinning animals, dogs, ground and tree discomfort, shaking

fleas squirrels, chipmunks), chills, pain in groin orrabbits, carnivores arm pits (swollen lymph

nodes), death

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Table 1. Some important wildlife diseases that affect humans (continued).

Disease Parasite Method of Wildlife Type of Human(Agent) Transmission Hosts Illness

Direct and Indirect

Tularemia Bacteria Contamination from Wild rodents, rabbits, Mild illness to severe(Francisella skinning animals, hares, carnivores, meningitis, pneumonia,tularensis) ticks, biting insects birds, hoofed animals ulcer at inoculation site,

swollen lymph nodes,death

Indirect

Tick-borne

Colorado tick fever Virus (coltivirus) Tick, Dermacentor Wild rodents (sciurids, High fever, headache,andersoni, D. porcupine), hares, muscle ache, lethargy,occidentalis rabbits, marmots, biphasic symptoms

carnivores

Rocky Mountain Rickettsia Tick, D. andersoni, Wild rodents, rabbits, Rapid onset, fever, head-spotted fever (Rickettsia rickettsii) D. variabilis, hares, carnivores, ache, muscle aches,

Amblyomma birds nausea, vomiting,americanum, abdominal pain, rash,Haemaphysalis loss of muscle control,leporispalustris possibly fatal

Ehrlichiosis Rickettsia Tick, species Unknown, possibly Fever, headache, nausea,(Ehrlichia unknown dogs and other vomiting, muscle aches,chaffeensis) carnivores fleeting rash

Lyme disease Bacteria Tick, Ixodes scapularis, Wild rodents Skin lesion (EM), fever,(Borrelia I. pacificus, A. (Peromyscus, chip- headache, fatigue,burgdorferi) americanum munks), raccoon, deer, muscle ache, stiff neck,

rabbits, birds cardiac and neurologicmanifestations, arthritis

Relapsing Bacteria Tick, Ornithodoros Wild rodents (chip- Rapid onset, severefever (Borrelia hermsii, B. hermsi, O. parkeri, munks, tree squirrels), headache, muscle weak-

parkeri, B. turicatae) O. turicata particularly in cabins ness, rigor, joint pain,and caves recurring fever

Babesiosis Protozoa Tick, I. scapularis Wild rodents (white- Gradual onset, loss of(Babesia microti) footed mice, meadow appetite, fever, sweating,

vole) fatigue, general muscleaches, prolongedanemia, sometimes fatal

Tularemia (listed above)

Mosquito-borne

St. Louis Virus Mosquito, Culex pipiens Birds (mostly song- Fever, headache,encephalitis (flavivirus) complex, Cx. tarsalis, birds and waterbirds), musculoskeletal aches,

Cx. nigripalpus some rodents malaise, low fatality

Eastern equine Virus Mosquito, Culiseta Birds (mostly song- Fever, intense headache,encephalitis (alphavirus) melanura, Aedes spp. birds and waterbirds), nausea, vomiting,

bats muscle, aches, confusion,coma, high fatality

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Table 1. Some important wildlife diseases that affect humans (continued).

Disease Parasite Method of Wildlife Type of Human(Agent) Transmission Hosts Illness

Indirect

Western equine Virus Mosquito Birds (mostly song- Fever, headache, nausea,encephalitis (alphavirus) Cx. tarsalis birds and waterbirds), vomiting, malaise, loss

jackrabbits, rodents of appetite, convulsions, low fatality

California Virus Mosquito Eastern chipmunk, Fever, irritability, head-encephalitis (bunyavirus) Ae. triseriatus tree squirrel, red fox, ache, nausea, vomiting,(LaCrosse) deer mouse loss of muscle control,

confusion, coma, lowfatality

Louse-borne

Louse-borne Rickettsia Body louse Humans, flying Onset variable, fever,typhus (Rickettsia Pediculus humanus, squirrels headache, chills, general

prowazekii) animal contact pains, prostration, skinrash after 5 to 6 days

Flea-borne

Flea-borne typhus Rickettsia Rat flea Domestic rats, wild Fever, severe headache,(Murine) (Rickettsia typhi) Xenopsylla cheopis rodents, opossum chills, general pains,

possibly skin rash

Plague (listed above)