A mosquito-borne virus that usually causes mild and self-limiting disease in humans, characterised by symptoms that resemble influenza or dengue fever (e.g., fever, headache, malaise, nausea). Central nervous system infection can lead to long-term neurological sequelae and death, particularly in children.
Occurs mainly in Central and South America, but cases have been reported in North America.
Large human outbreaks have been linked to epizootic infection, in which equine species are a major amplifying host for the virus. Enzootic infection, which likely utilises rodents as amplifying hosts, may be the cause of up to 10% of cases that are clinically misdiagnosed as dengue fever.
Diagnosis is based on clinical presentation and geographical clues. Confirmation of diagnosis is via reverse transcription-polymerase chain reaction, viral isolation, or serology. Differentiation from malaria and dengue fever is important.
There is no specific treatment; supportive care is advocated.
Avoidance of mosquito bites is the best method of prevention. There is no licensed vaccine for use in humans, although a live-attenuated vaccine is available for laboratory personnel at risk of occupational exposure.
Infection caused by Venezuelan equine encephalitis virus (VEEV), a positive-sense single-stranded RNA virus (family: Togaviridae; genus: Alphavirus) transmitted by mosquitoes. Mosquitoes transmit the virus by feeding on the blood of animals infected with VEEV (horse or rodent), and passing it on to non-infected humans or animals when it feeds again.
In humans infected with VEEV, the incubation period ranges from 1 to 10 days, and the duration of acute illness is typically days to weeks, depending on severity. VEEV infection may be asymptomatic, or result in mild self-limiting symptoms that resemble influenza or dengue fever (e.g., fever, malaise, headache, nausea); however, some infections may result in more serious neurological complications (e.g., seizures and coma), haemorrhage, or death. Overall mortality during outbreaks of VEEV have rarely exceeded 1%. Mortality occurs mainly in children, and is generally attributable to consequences of neurological involvement.
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History and exam
Key diagnostic factors
- presence of risk factors
- acute onset of fever
Other diagnostic factors
- retro-orbital pain
- altered mental status
- gastrointestinal bleeding
- sore throat
- lethargy, drowsiness, or confusion
- ataxia/gait abnormalities
- behavioural abnormalities
- stupor, somnolence, or coma
- neck stiffness (nuchal rigidity)
- living and/or working in or near tropical forests in Central or South America
- fishing in or near tropical forests in Central or South America
- age <15 years
- occupational exposure (laboratory)
1st investigations to order
- reverse transcription-polymerase chain reaction (RT-PCR)
- enzyme-linked immunosorbent assay (ELISA)
Investigations to consider
- plaque reduction neutralisation test (PRNT)
- viral isolation
- cerebrospinal fluid cell count, chemistries (glucose, protein), and viral isolation
- FBC (including haematocrit)
- chest x-ray
- head CT
- brain MRI
- rapid malaria antigen test or malaria smear
Amy Vittor, MD, PhD
Division of Infectious Disease and Global Medicine
University of Florida
AV is funded by the National Institute of Allergy and Infectious Diseases (NIAID) for work on host susceptibility and emerging alphaviruses (2016-2021); however, the funding supports new insights in the field only, it does not directly impact any articles produced. AV is a recipient of an NIH NIAID K08 award. AV is also the author of a reference cited in this topic.
Miguel G. Madariaga, MD, MSc, FACP
Infectious Diseases Consultant
Naples Community Hospital
MGM declares that he has no competing interests.
Stalin Vilcarromero, MD
US Naval Medical Research Unit 6 (NAMRU-6)
SV declares that he has no competing interests.
- Malaria infection
- Dengue fever
- Chikungunya virus
- Management of suspected viral encephalitis in adults- Association of British Neurologists and British Infection Association national guidelines
- Management of suspected viral encephalitis in children- Association of British Neurologists and British Paediatric Allergy, Immunology and Infection Group national guidelines
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