


Venezuelan Equine Encephalitis

Causative Agent:
Venezuelan Equine Encephalitis (VEE) is a mosquito-borne illness caused by an alphavirus of the Togaviridae family.

Routes of Exposure:
Humans are primarily exposed to VEE through the bite of an infected mosquito.

Infective Dose & Infectivity:
The infective dose is considered to be 10-100 organisms. All people are considered susceptible though children are more likely to be severely affected.

Incubation Period:
The incubation period is usually 2-6 days; though it can be as short as 1 day.

Clinical Effects:
VEE is characterized by inflammation of the meninges of the brain and of the brain itself, thus accounting for the predominance of CNS symptoms in the small percentage of infections that develop encephalitis. The disease is usually acute, prostrating and of short duration. Illness begins suddenly with generalized malaise, spiking fevers, rigors, severe headache, photophobia, and myalgias. Nausea, vomiting, cough, sore throat, and diarrhea may follow. Full recovery takes 1-2 weeks.

The overall mortality rate for VEE is less than 1%, but is somewhat higher among children and older adults.

VEE infection generally occurs when a person is bitten by an infected mosquito. VEE is highly infectious when aerosolized. There is no evidence of human-to-human transmission, even though VEE virus can be found in human throat swabs.

Primary contaminations & Methods of Dissemination:
As a bioterrorism weapon, VEE would most likely be delivered via aerosolization.

Secondary Contamination & Persistence of organism:
Secondary transmission does not occur and VEE particles are not considered to be stable in the environment.

Decontamination & Isolation:

  • Equipment, clothing & other objects – 0.5% hypochlorite solution (one part household bleach and 9 parts water = 0.5% solution), other EPA approved disinfectants, and heat are effective for environmental decontamination.

Laboratory testing:
Virus can be isolated from serum, and in some cases throat swab specimens. An increase in VEE IgG antibody in paired sera, or VEE specific IgM present in a single serum sample indicate recent infection.

Therapeutic Treatment:

Prophylactic Treatment:
A live, attenuated vaccine is available as an investigational new drug. A second, formalin-inactivated, killed vaccine is available for boosting antibody titers in those initially receiving the live vaccine.

Differential Diagnosis:
The differential diagnosis includes a number of viral and bacterial infections including arenaviruses, cytomegalovirus, dengue fever, viral hepatitis, herpes simplex encephalitis, influenza, leptospirosis, malaria, bacterial meningitis, Q fever, St. Louis encephalitis, West Nile encephalitis, yellow fever, Colorado tick fever, and the early prodrome of measles.


