Microbiology · Other viruses and prions
Equine encephalitis viruses and Mayaro virus !
- Virus
- Enveloped
- For completeness
Mosquito-borne alphaviruses that cause fever and sometimes encephalitis in horses and people; Mayaro causes fever with joint pain.
Updated 2026-11-01
Also called: Venezuelan equine encephalitis, eastern equine encephalitis, western equine encephalitis, Mayaro fever
At a glance
- Shape
- Spherical, icosahedral capsid
- Genome
- Single-stranded, positive-sense RNA
- Envelope
- Enveloped
- Family
- Togaviridae, genus Alphavirus
- Size
- About 70 nm
Morphology
- Envelope with the E1 and E2 glycoproteins
- Icosahedral capsid
- Same genus as chikungunya
Transmission
- Bite of infected mosquitoes
- Venezuelan equine encephalitis: horses and donkeys develop high viraemia and amplify the virus in epidemics
- Eastern and western encephalitis: a bird-mosquito cycle; horses and humans are dead-end hosts
- Mayaro: Haemagogus mosquitoes of forest areas
Reservoir: Wild rodents (enzootic VEE), birds (eastern and western), non-human primates (Mayaro, possibly)
Vector: Mosquitoes of several genera: Culex, Aedes, Psorophora, Culiseta and Haemagogus, depending on the virus and region.
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Multiplies in lymphoid tissue and reaches the blood
- Some cross into the nervous system and cause encephalitis
- Eastern equine encephalitis is the deadliest and leaves neurological sequelae in many survivors
Diseases it causes
- Venezuelan, eastern and western equine encephalitis Viral encephalitis (herpes simplex encephalitis) →
- Mayaro fever with arthralgia (a chikungunya-like illness)
Clinical picture
- Fever, headache, myalgia and vomiting
- Encephalitis: drowsiness, seizures, behaviour change; more severe in children and older adults
- Mayaro: joint pain and swelling that can last weeks or months
Diagnosis
- IgM in serum or cerebrospinal fluid
- RT-PCR in the acute phase
- Consider Mayaro in the differential of dengue, chikungunya and Zika
Treatment
No specific antiviral: supportive treatment and neurological care in encephalitis.
Drug class only; doses and regimens are set by the clinician from the current guideline.
Prevention
- Avoid mosquito bites: repellent, long clothing, bed nets
- Vaccinating horses against Venezuelan equine encephalitis and restricting equine movement during outbreaks
- Control of mosquito breeding sites
Test yourself
Think of the answer, then tap the question to see it.
What role do horses play in Venezuelan equine encephalitis epidemics?
They are amplifying hosts: they develop high viraemia and feed the mosquitoes.
Which genus do the equine encephalitis viruses and Mayaro virus belong to?
Genus Alphavirus, family Togaviridae, like chikungunya.
Which Colombian region had a large Venezuelan equine encephalitis epidemic in 1995?
La Guajira.
Which equine encephalitis is the deadliest?
Eastern equine encephalitis.
Related
Related conditions
← Back to the group: Other viruses and prions
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Venezuelan Equine Encephalitis -- Colombia, 1995 (CDC (MMWR), 1995); About Eastern Equine Encephalitis Virus | Eastern Equine Encephalitis Virus | CDC (CDC, 2024); Epidemiological Alert: Mayaro Fever (PAHO/WHO, 2019).
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Representative model, for educational purposes only.