Biological Weapons --
Venezuelan Equine Encephalitis

The human infective dose for VEE is considered to be 10-100 organisms, which is one of the principal reasons that VEE is considered a militarily effective biowarfare agent. Neither the population density of infected mosquitoes nor the aerosol concentration of virus particles has to be great to allow significant transmission of VEE in a BW attack. VEE particles are not considered stable in the environment, and are thus not as persistent as the bacteria responsible for Q fever, tularemia or anthrax.
Symptoms Incubation period is 1 to 6 days, but may be as long as 15 days with a sudden onset of symptoms. They include fever, malaise, and headache. Other symptoms that may appear include myalgia (72%), vomiting (50%), drowsiness (40%), chills (20%), sore throat (20% ), and diarrhea (20%).

Fever can come and go. Patients may be incapacitated by malaise and fatigue for 1 - 2 weeks. Less than 1% of adults develop severe encephalitis (swelling of the brain) featuring meningismus, lack of muscular coordination, seizures, and coma.

Up to 30% of survivors of severe disease have permanent neurologic conditions, which include seizures and paralysis and various degrees of dementia.

How does it spread?

This disease is spread by mosquitoes. Aerosol transmission has occurred in laboratory settings, but is not known to occur naturally. There is no evidence of direct human-to-human or horse-to-human transmission.

The virus can be destroyed by heat (80oC for 30 min) and standard disinfectants.

Diagnosis Lab tests may reveal a decrease in white blood cells. Specific diagnosis depends on virus isolation, serology, or both. Virus may be collected from the nose and throat for 3 days after the onset of symptoms.

No specific treatment is available for this disease. Supportive care may include aggressive airway management and anti-fever and anticonvulsant drug administration.

At present, there is no pre-exposure or post-exposure immunoprophylaxis available. Other treatment info can be found here

A live, weakened 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 first vaccine.

The case fatality rate in adults is approximately 1% of all cases, but may reach 10% with central nervous system involvement. However, outcomes are significantly worse for young and elderly patients, with fatalities ranging from 4-35%.


USAMRIID's Medical Management of Biological Casualties Handbood; Fourth Edition February 2001; pages 9-10;
Federation of American Scientists;
Virtual Naval Hospital: Treatment of Biological Warfare Agent Casualties;
CBRNE - Biological Warfare Agents;

All contents © 2001 Stan and Holly Deyo. All rights reserved.

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