Viral Diseases

Animals Involved
Sheep, goats, camels

Known Distributions
Middle East, mainly reported in Saudi Arabia, also Egypt

Probable Means of Spreading
Ticks (Ornithodoros and Hyalomma spp); direct contact with animal meat via broken skin or ingestion of unpasteurized camel milk linked to some cases

Clinical Manifestations in People
Febrile illness, often with GI signs (eg, vomiting, abdominal pain); encephalitic/neurologic and hemorrhagic signs in some; case fatality up to 25% in early reports, recently <1%

Animals Involved
Avian influenza viruses in wild and domestic birds, especially poultry; uncommon in mammals

Known Distributions
Worldwide, distribution of strains varies

Probable Means of Spreading
Usually by contact with infected poultry; avian viruses may be shed in respiratory secretions and feces

Clinical Manifestations in People
Avian influenza viruses can cause conjunctivitis, human influenza­like illness, or severe disease with multiorgan dysfunction, death; severity of disease varies with influenza strain

Animals Involved
Natural hosts unknown; horses, brushtail possums may be hosts

Known Distributions
Australia

Probable Means of Spreading
Mosquito bites; Culex annulirostris and Aedes spp implicated

Clinical Manifestations in People
Resembles disease caused by Ross River virus (see entry later in this table) but seems to persist longterm in fewer patients, rash more common

Animals Involved
Water buffalo, cattle

Known Distributions
Indian subcontinent (south Asia), Egypt, Indonesia

Probable Means of Spreading
Skin contact with infected animals, often when milking

Clinical Manifestations in People
Pox skin lesions mainly on hands, face, legs, buttocks; occasionally lymphadenopathy, fever, malaise

Animals Involved
Many wild and domestic mammals

Known Distributions
North and South America, Europe, Africa, Asia; possibly worldwide; distribution of each virus varies

Probable Means of Spreading
Mosquito bites

Clinical Manifestations in People
Syndromes, severity vary with the virus; flu­ like illness, meningitis, or encephalitis common with North American viruses

Animals Involved
Old World camelids, possibly other species

Known Distributions
Middle East, Asia, Africa, possibly other areas; human cases recently described in India in camel handlers, rare unconfirmed cases suggested in other locations

Probable Means of Spreading
Direct contact

Clinical Manifestations in People
Skin lesions similar to cowpox, variola virus infections

Animals Involved
Sylvatic cycle in nonhuman primates, possibly rodents in Africa; virus thought to be maintained in people in Asia, but sylvatic cycle may also exist

Known Distributions
Asia, Africa

Probable Means of Spreading
Mosquito bites (especially Aedes spp)

Clinical Manifestations in People
Febrile illness, may have rash and/or GI signs; arthralgia, especially in small joints, and myalgia prominent, may persist for months; myocarditis, neurologic signs, hemorrhages reported in a few cases

Animals Involved
Rodents; also found in porcupines, lagomorphs, deer, elk, and other mammals

Known Distributions
Rocky Mountain region of North America

Probable Means of Spreading
Tick bites (primary vector is Dermacentor andersoni)

Clinical Manifestations in People
Nonspecific febrile illness; pharyngitis, rash, or GI signs possible; biphasic or triphasic in some; complications (eg, neurologic signs, hemorrhages, pericarditis, myocarditis, orchitis) uncommon but can occur in severe cases; deaths rare

Animals Involved
Sheep, goats, camelids, reindeer, wild ungulates; rare cases in dogs

Known Distributions
Worldwide

Probable Means of Spreading
Occupational exposure via contact with broken skin (both live animals and meat processing)

Clinical Manifestations in People
Papule(s) that umbilicate and ulcerate, usually on hands; dissemination rare; large lesions refractory to treatment can be seen in immunosuppressed

Animals Involved
Rodents are usual reservoir host; also in domestic and wild cats, occasionally cattle, other mammals

Known Distributions
Parts of Europe and Asia

Probable Means of Spreading
Contact exposure via broken skin, bites, scratches

Clinical Manifestations in People
Papules, vesicles that become pustular, to ulcerative nodules, scars; single or multiple lesions, often on hands; regional adenopathy and malaise, flu­like symptoms in some; lesions remain localized in healthy people; more extensive or generalized disease may be seen in children, people with eczema, immunocompromised; severe cases can involve respiratory mucosa; rare fatal cases (eg, complications of encephalitis)

Animals Involved
Cattle, rodents, sheep, goats, hares, other mammals, some birds

Known Distributions
Africa, Middle East, central Asia, southeastern Europe; appears to be spreading

Probable Means of Spreading
Tick bites, especially Hyalomma but also Rhipicephalus, Dermacentor, other species; skin contact with animal or human blood or tissues or crushed ticks; ingestion of unpasteurized milk

Clinical Manifestations in People
Fever, headache, pharyngitis, abdominal symptoms, petechial rash, hemorrhage, hepatitis, other organ involvement in some cases; very severe in pregnant women; case fatality rate 3%–50%, varies with region

Animals Involved
Birds are principal reservoir hosts in North America, snakes might have role in overwintering virus; rodents, marsupials might be reservoir hosts in South America; clinical cases seen in equids and occasionally other mammals and birds; mammals are almost always dead­end hosts

Known Distributions
Western hemisphere

Probable Means of Spreading
Mosquito bites; Culiseta melanura important in maintenance cycle in birds in North America; various mosquito species (Aedes, Coquillettidia, Culex) can transmit to people

Clinical Manifestations in People
Nonspecific febrile illness may be followed by severe encephalitis, especially with North American lineage; neurologic sequelae common after encephalitis; case fatality rate 30%–70% with North American lineage; more severe in infants and elderly

Animals Involved
Bats are reservoir hosts for Zaire ebolavirus and suspected reservoir hosts for others; primates, duikers, possibly other mammals can be infected

Known Distributions
Africa

Probable Means of Spreading
Contact with infected tissues (especially nonhuman primates and duikers); probable transmission from bats in caves

Clinical Manifestations in People
Initially nonspecific febrile illness; maculopapular rash with desquamation; mild to severe bleeding tendency develops a few days after onset; mortality rate 36%–90%, varies with isolate

Animals Involved
Rodents may be reservoir hosts; also in swine, nonhuman primates, elephants, other mammals, and wild birds

Known Distributions
Worldwide in animals

Probable Means of Spreading
Uncertain

Clinical Manifestations in People
Nonspecific febrile illness, sometimes with GI signs, and/or decreased reflexes have been reported in adults, with recovery within several days; CNS signs, including paralysis, have been reported in children

Animals Involved
Cattle, swine, sheep, goats, other cloven­ hoofed animals (Artiodactyla), a few mammals in other orders

Known Distributions
Asia, Africa, Middle East, South America

Probable Means of Spreading
Contact exposure, often in laboratories or other high concentrations of virus

Clinical Manifestations in People
People may become temporary nasal carriers of virus but do not usually become ill; mild influenza ­like disease with vesicular lesions occurs very rarely

Animals Involved
Rodents; each virus tends to be associated with a single reservoir host

Known Distributions
North and South America

Probable Means of Spreading
Aerosols from rodent excretions and secretions; contact with broken skin and mucous membranes; rodent bites

Clinical Manifestations in People
Prodromal stage with nonspecific febrile illness; followed by respiratory failure, cardiac abnormalities; hemorrhagic signs possible with South American viruses; significant kidney disease uncommon; mortality rate varies with the virus, but can reach 40%–60%

Animals Involved
Rodents; each virus tends to be associated with a single reservoir host, but Seoul virus is carried by both Rattus norvegicus and R rattus

Known Distributions
Europe, Asia; Seoul virus is worldwide

Probable Means of Spreading
Aerosols from rodent excretions and secretions; contact with broken skin and mucous membranes; rodent bites

Clinical Manifestations in People
Prodromal stage with abrupt onset of fever, headache, back pain, sometimes petechiae, GI signs (may be severe); followed by hypotension, renal signs to renal failure with oliguria; hemorrhage, other syndromes in some; mortality rate varies with the virus, from <1% (Puumala virus) to 10%–15% (Hantaan virus)

Animals Involved
Fruit bats are normal reservoir host; horses can be infected

Known Distributions
Australia

Probable Means of Spreading
Direct contact with infected animals (all human cases have been linked with horses) or contaminated tissues

Clinical Manifestations in People
Respiratory infection, encephalitis (including recurrent encephalitis); few cases described but several were fatal

Animals Involved
People; animals, including swine, wild boar, deer, rabbits, ferrets, rats, mongoose, others; swine and probably other hosts are reservoirs for human infections

Known Distributions
Worldwide; human and zoonotic genotypes may differ in prevalence between areas

Probable Means of Spreading
Fecal­oral spread; consumption of raw or undercooked meat and liver; waterborne, contact with animal reservoirs

Clinical Manifestations in People
Mild, self­limiting hepatitis to liver failure, more severe in pregnancy and can result in abortion, death of newborn, premature birth; usually acute, but can be chronic in organ­ transplant patients; case fatality rate <1% to 4% in general population, up to 20% in pregnant

Animals Involved
Carried in genus Macaca (Old World macaques), with lifelong latency and potential for periodic shedding after infection; other nonhuman primates susceptible; cell cultures

Known Distributions
Worldwide, can be common, especially in closed groups of macaques; human cases rare

Probable Means of Spreading
Monkey bites and scratches, contamination of mucous membranes with infected saliva, secretions

Clinical Manifestations in People
Influenza­like symptoms; vesicular skin lesions, pain, or itching around wound, followed by severe encephalitis with seizures, paralysis, coma; 85% mortality rate

Animals Involved
Swine, wild birds are important maintenance hosts; horses ill but epidemiologically unimportant in amplification; other mammals, reptiles, amphibians may be infected, usually asymptomatically

Known Distributions
Asia, Australia, Papua New Guinea, Pacific islands from Japan to the Philippines

Probable Means of Spreading
Mosquito bites (Culex tritaeniorhynchus) important in maintenance cycle, other Culex and Aedes spp can transmit); also through broken skin or mucous membranes after direct contact with infected tissues

Clinical Manifestations in People
Fever, chills, myalgia, severe headache, GI symptoms; can progress to severe encephalitis; neurologic sequelae very common in survivors of encephalitis; case fatality rate 15%–30%

Animals Involved
Rodents, shrews, other small mammals might be reservoirs (uncertain); affects monkeys; possible infections in other mammals, birds

Known Distributions
India

Probable Means of Spreading
Tick bites (especially Haemaphysalis spinigera, also others)

Clinical Manifestations in People
Nonspecific febrile illness; course may be biphasic; hemorrhagic signs (eg, ecchymoses, purpura, petechiae, GI bleeding, epistaxis) and/or neurologic signs possible in second stage; prolonged convalescence in many; case fatality rate ~3%

Animals Involved
Chipmunks, squirrels are major amplifying hosts; rabbits, foxes, and other mammals can be infected

Known Distributions
North America

Probable Means of Spreading
Mosquito bites

Clinical Manifestations in People
Many cases mild and flu­like; meningitis or encephalitis with seizures, paralysis, and focal neurologic signs possible; most cases in children; estimated case fatality rate <1% in cases with encephalitis

Animals Involved
Wild rodents, usually multimammate mouse

Known Distributions
West Africa

Probable Means of Spreading
Contact with rodent excretions, secretions, or tissues; aerosols

Clinical Manifestations in People
Gradual onset of nonspecific febrile illness, may be followed by chest pain, cough, GI signs, hepatitis; severe swelling of head and neck, hypotension/shock can develop; pleural/pericardial effusions; hemorrhagic syndrome less common; overall mortality rate 1% in endemic areas; case fatality rate 20% among hospitalized patients

Animals Involved
Sheep, goats, also in llamas, cattle, horses, other domestic and wild mammals, grouse, ptarmigan

Known Distributions
UK, Northern Ireland; also reported in Norway, Spain; uncommon in people

Probable Means of Spreading
Tick bites (Ixodes ricinus); aerosol exposure in laboratory, contamination of skin wounds, contact with infected animals; possibly ingestion of milk

Clinical Manifestations in People
Biphasic influenza­like illness, sometimes followed by meningitis or meningoencephalitis, paralysis, joint pain in second phase; not usually fatal

Animals Involved
Reservoir mainly house mouse; can be maintained in some other mice, hamster populations; also infects guinea pigs, chinchillas, rats, nonhuman primates, some other mammals

Known Distributions
Worldwide

Probable Means of Spreading
Contact with host excretions and secretions; bites; possibly ingestion

Clinical Manifestations in People
Ranges from mild flu­like illness to biphasic with meningitis in second phase; complications (eg, arthritis, parotitis, orchitis) possible; can cause congenital defects (CNS defects, chorioretinitis, and other ocular lesions) or abortion; rarely fatal in immunocompetent (overall case fatality rate <1%)

Animals Involved
Bats are reservoir hosts; primates can be infected

Known Distributions
Africa

Probable Means of Spreading
Contact with infected tissues (especially nonhuman primates); probable transmission from bats in caves

Clinical Manifestations in People
Initially nonspecific febrile illness; maculopapular rash with desquamation; hepatitis; mild to severe bleeding tendency develops a few days after onset; mortality rate 20%–88%, varies with isolate

Animals Involved
Fruit bats are normal reservoir host; pigs can also be reservoir

Known Distributions
Australia

Probable Means of Spreading
Close direct contact with tissues, amniotic fluid or blood of pigs reported in human cases

Clinical Manifestations in People
Severe illness with fever, severe headache, myalgia, lymphadenopathy, drenching sweats, macular rash

Animals Involved
Unknown reservoir host, possibly bats; source of infection for people uncertain, camels implicated

Known Distributions
Middle East

Probable Means of Spreading

Clinical Manifestations in People
Pneumonia, more likely in people with coexisting illness or immunosuppression but also in healthy; ~50% of known cases were fatal

Animals Involved
Cattle

Known Distributions
Worldwide

Probable Means of Spreading
Skin contact (especially broken skin) with lesions on cow’s udder or mouth of calf; also from fomites

Clinical Manifestations in People
Papular to nodular red skin lesions; self­ limiting

Animals Involved
Nonhuman primates, some wild and pet rodents, including Gambian rats, dormice, prairie dogs, African squirrels, some other mammals such as opossums; full host range uncertain

Known Distributions
West and central Africa

Probable Means of Spreading
Contact with lesions, blood or body fluids, fomites; bites; aerosols during close contact

Clinical Manifestations in People
Smallpox­like disease; flu­like symptoms followed by maculopapular rash, which develops into vesicles, pustules, scabs; lymphadenopathy prominent; respiratory signs, encephalitis possible; case fatality rate varies with strain, <1% to 10%–17% or higher; milder in those vaccinated for smallpox

Animals Involved
Wild water birds

Known Distributions
Australia, New Guinea

Probable Means of Spreading
Mosquito bites (Culex annulirostris)

Clinical Manifestations in People
Asymptomatic or mild nonspecific febrile illness in majority; encephalitis, often with neurologic sequelae, or poliomyelitis­like flaccid paralysis in small number of patients; case fatality rate 15%–30% in encephalitic form

Animals Involved
Rodents

Known Distributions
South America, related viruses might exist among rodents in Mexico

Probable Means of Spreading
Viruses found in rodent excretions, secretions, tissues; inhalation of aerosolized virus or direct contact with mucous membranes or broken skin

Clinical Manifestations in People
Gradual onset of nonspecific signs, including myalgia, headache, and fever; may develop petechial or ecchymotic hemorrhages, bleeding, CNS signs, hypotension/shock; case fatality rate in untreated Bolivian hemorrhagic fever 5%–30%, untreated Argentine hemorrhagic fever 15%–30%

Animals Involved
Domestic and wild birds

Known Distributions
Mildly virulent (lentogenic, mesogenic strains) are found worldwide; highly virulent (velogenic)
strains found in Asia, the Middle East, Africa, Central and South America, parts of Mexico; also in cormorants in USA

Probable Means of Spreading
Occupational exposure, usually after contact with large amounts of virus

Clinical Manifestations in People
Highly virulent (velogenic) strains can cause self­limiting conjunctivitis, possibly other syndromes

Animals Involved
Voles, muskrats; also found in other animals

Known Distributions
Siberia

Probable Means of Spreading
Tick bites (Dermacentor spp); direct contact with body fluids or carcasses of muskrats and possibly other animal hosts

Clinical Manifestations in People
Biphasic febrile illness with headache, GI signs, ± hemorrhages (nose, gums, lungs, uterus); CNS signs in minority of patients; mortality rate <3%

Animals Involved
Rodents (groundhog, squirrels, mice) and other small mammals thought to be reservoirs

Known Distributions
North America, eastern Russia

Probable Means of Spreading
Ixodes spp ticks, also found in Dermacentor andersoni

Clinical Manifestations in People
Nonspecific febrile illness; may progress to neurologic signs, which may be severe; some cases fatal

Animals Involved
Wild and domestic canids, Mustelidae, Viverridae, Procyonidae, and order Chiroptera (bats) are important reservoir hosts; all mammals are susceptible; bats are reservoir hosts for Duvenhage virus, Australian bat lyssavirus, and European bat lyssaviruses; Mokola virus carried in rodents and shrews

Known Distributions
Rabies is worldwide with some exceptions: completely absent from some islands; countries also considered rabies­free if no cases in people or domestic animals for 2 yr; rabies­ related lyssaviruses found only in Eastern Hemisphere (distribution varies)

Probable Means of Spreading
Bites of diseased animals; aerosols in closed environments

Clinical Manifestations in People
Paresthesias or pain at bite site; nonspecific prodromal signs such as fever, myalgia, malaise; mood changes progress to paresthesias, paresis, seizures, and many other neurologic signs; survival in clinical cases thought to be very rare

Animals Involved
Sheep, goats, cattle, buffalo, African buffalo, camels, nonhuman primates; squirrels and other rodents; puppies and kittens

Known Distributions
Africa, foci on Arabian peninsula, Indian subcontinent

Probable Means of Spreading
Mosquito bites (Aedes spp and Culex triteniorynchus); contact with tissues

Clinical Manifestations in People
Influenza­like febrile illness in most; complications, including hemorrhagic fever, meningoencephalitis in <5%; ocular disease in 1%–10%; other syndromes include acute renal failure or thrombosis; death uncommon except with hemorrhagic syndrome

Animals Involved
Marsupials, including wallaby, brushtail possum, might be natural hosts; dusky rat also proposed; people, horses, ruminants, pigs, rabbits, other mammals (minor hosts) may also be a source of virus during epidemics

Known Distributions
Australia, South Pacific Islands

Probable Means of Spreading
Mosquito bites (especially Culex annulirostris and Aedes spp)

Clinical Manifestations in People
Mild fever, arthralgia ± arthritis, headache, rash; small joints most affected but large joints can also be involved; arthralgia, myalgia, lethargy may persist for months

Animals Involved
Bats are thought to be reservoir hosts; can also infect palm civets, raccoon dogs, cats, pigs, ferrets, rodents, nonhuman primates, other mammals

Known Distributions
China, Southeast Asia

Probable Means of Spreading
Contamination of mucous membranes with respiratory droplets or virus on fomites; possibly aerosol transmission

Clinical Manifestations in People
Fever, myalgia, headache, diarrhea, cough; viral pneumonia with rapid deterioration; case fatality rate 15%

Animals Involved
Birds (passeriforms suspected as main reservoirs/amplifying hosts); occasionally found in other vertebrates

Known Distributions
Virus widespread in Eastern hemisphere; human cases tend to occur in
limited geographic regions

Probable Means of Spreading
Mosquito bites; Culex and Culiseta, also others

Clinical Manifestations in People
Fever, arthritis, rash, prominent myalgia; nausea, vomiting, mild jaundice in some; joint pain can persist for months; seems to be mild or asymptomatic in most children; no fatal cases reported

Animals Involved
Wild birds, domestic fowl; rodents, bats, other mammals might also maintain viruses in South America

Known Distributions
Western hemisphere

Probable Means of Spreading
Mosquito bites (Culex tarsalis, C pipiens­ quinquefasciatus complex, C nigripalpus, also reported in other genera)

Clinical Manifestations in People
Flu­like illness sometimes followed by meningitis or encephalitis, focal neurologic signs, dysuria; more severe in elderly and those with debilitating diseases; case fatality rate of 5%–20% reported in epidemics

Animals Involved
Usually in pigs; also turkeys; can infect mink, ferrets

Known Distributions
Worldwide

Probable Means of Spreading
Usually by contact with infected animals; swine influenza viruses occur in respiratory secretions

Clinical Manifestations in People
Seems to resemble human influenza; severity of disease varies; fatal cases have been reported uncommonly

Animals Involved
Usually in pigs; also turkeys; can infect mink, ferrets

Known Distributions
Worldwide

Probable Means of Spreading
Usually by contact with infected animals; swine influenza viruses occur in respiratory secretions

Clinical Manifestations in People
Seems to resemble human influenza; severity of disease varies; fatal cases have been reported uncommonly

Animals Involved
Nonhuman primates

Known Distributions
Asia, Africa, and in monkey colonies

Probable Means of Spreading
Direct contact through broken skin; mosquitoes suspected to be vector in Africa

Clinical Manifestations in People
Nonspecific febrile illness and papulovesicular or nodular lesions (lesions may be pruritic or tender), often on extremities; more than one or two skin lesions uncommon

Animals Involved
Small mammals especially rodents; also in goats, sheep, dogs, and other mammals; birds

Known Distributions
Eurasia; TBEV­ Eu mainly Europe to former USSR; TBEV­FE mainly Asia to former USSR; TBEV­Sib mainly in Siberia

Probable Means of Spreading
Tick bites (mainly Ixodes ricinus and I persculatus; also other species); may be ingested in milk

Clinical Manifestations in People
Often biphasic, with flu­like febrile illness in initial stage; neurologic signs from mild meningitis to severe encephalitis in some; myelitis or flaccid poliomyelitis­like paralysis (usually arms, shoulders, levator muscles of head); possibility of chronic and progressive forms, especially with TBEV­Sib; case fatality rate <2% (TBEV­Eu), 2%–3% (TBEV­Sib); case fatality rate 20%–30% in TBEV­FE may be based on severe cases

Animals Involved
Birds

Known Distributions
Africa, Europe

Probable Means of Spreading
Mosquito bites (Culex spp)

Clinical Manifestations in People
Very few cases identified: fever with rash, fever with jaundice, or meningoencephalitis

Animals Involved
Reservoir uncertain; found in wild rodents, cattle, horses, nonhuman primates

Known Distributions
Appear to be endemic in Brazil

Probable Means of Spreading
Direct contact

Clinical Manifestations in People
Pox skin lesions (papules, pustules, ulcerative nodules), may be accompanied by fever, lymphadenopathy

Animals Involved
Enzootic subtypes maintained in rodents, other small mammals, bats; epizootic subtypes amplified in equids; occasionally in other mammals and birds

Known Distributions
Western hemisphere; enzootic strains Florida to South America; epizootic strains emerge in South America, spread

Probable Means of Spreading
Mosquito bites (Aedes, Culex, and Psorophora spp); exposure to aerosolized debris from infected laboratory rodents; laboratory accidents

Clinical Manifestations in People
Most have nonspecific febrile illness, can be followed by neurologic signs; <5% children, <1% adults progress to encephalitis with case fatality rate of 10%–35% (highest rates in children <5 yr old)

Animals Involved
Swine, cattle, horses; occasionally in South American camelids, sheep, and goats; also rodents; serologic evidence of infection in many wild mammals, especially bats

Known Distributions
North and South America; most likely not endemic north of Mexico but sporadic outbreaks

Probable Means of Spreading
Contact with animals or in laboratory, probably also from insect bites, including mosquitoes and biting flies (Phlebotomus spp, Lutzomyia spp, and black flies)

Clinical Manifestations in People
Usually asymptomatic; may develop acute, febrile, flu­like illness; vesicles can be found in mouth, pharynx, or inoculation site (eg, hands); self­-limiting

Animals Involved
Ruminants, especially sheep, goats; also evidence of infection in other mammals, including lemurs; can infect birds

Known Distributions
Southern Africa, southeast Asia

Probable Means of Spreading
Mosquito bites (mainly Aedes spp, possibly others); also by contact with contaminated material

Clinical Manifestations in People
Nonspecific febrile illness ± maculopapular rash or ocular signs in some; few cases described but seems to be self­-limiting

Animals Involved
Birds are primary reservoir hosts; also affects horses, other mammals, alligators, possibly other reptiles and amphibians

Known Distributions
Eastern and Western hemisphere

Probable Means of Spreading
Mosquito bites (primarily Culex univittatus, Culex spp); also by handling infected birds or reptiles or their tissues

Clinical Manifestations in People
Nonspecific febrile illness, occasionally with rash; some cases progress to encephalitis, meningitis, and/or acute flaccid paralysis that resembles poliomyelitis; occasionally other syndromes; worse in elderly and immunocompromised; case fatality rate ~10% in all patients with neurologic disease, but higher in elderly

Animals Involved
Birds are reservoir hosts, may also cycle in jackrabbits, rodents; equids, other mammals are incidental hosts; virus also found in reptiles, amphibians

Known Distributions
Americas

Probable Means of Spreading
Mosquito bites (Aedes, Culex, and Ochlerotatus spp); Culex tarsalis important in maintenance cycle in birds

Clinical Manifestations in People
Nonspecific febrile illness may be followed by encephalitis in infants and children, uncommonly in adults; case fatality rate 3%– 4%

Animals Involved
Nonhuman primates

Known Distributions
South America, Africa

Probable Means of Spreading
Mosquito bites (Haemagogus spp and Sabethes spp in jungle cycles in South America, Aedes spp in jungle cycles in Africa)

Clinical Manifestations in People
Nonspecific, mild to severe febrile illness followed by liver and renal failure in some; hemorrhages (eg, epistaxis, hematemesis, melena, uterine hemorrhage) and often jaundice in severe cases; cases with hemorrhages often fatal