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.
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| 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.
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How does it spread?
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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.
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| 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.
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Treatment
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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
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Vaccine
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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.
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Mortality
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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%.
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Sources:
USAMRIID's Medical Management of Biological Casualties Handbood;
Fourth Edition February 2001; pages 9-10; http://usamriid.detrick.army.mil/education/bluebook/bluebook.pdf
Federation of American Scientists; http://www.fas.org/nuke/intro/bw/agent.htm
Virtual Naval Hospital: Treatment of Biological Warfare Agent
Casualties; http://www.vnh.org/FM8284/index.html
CBRNE - Biological Warfare Agents; http://www.emedicine.com/emerg/topic853.htm
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