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Key Diagnostic Tests.

• Virus isolation - the virus is only detectable at early stages of infection and this may be of more use in determining the spread of an attack than in diagnosis.
• Leukopenia early followed by leukocytosis;
• Detection of antigens or antibody to the agent in the blood (serology);
• ELISA is available

After an incubation of 2-6 days (as little as one day has been seen), there is a sudden onset of flu-like symptoms including a severe headache, chills, fever, retro-orbital pain (pain behind the eyes), congestion, nausea and vomiting. Lymphadenopathy is seen in about a third of cases. Most cases are mild and symptoms last 3-5 days. The disease can be biphasic with a return of more severe symptoms at 6-9 days after onset.

In severe cases the virus invades the central nervous system leading to encephalitis disorientation, convulsions, paralysis and coma.   Adults are relatively resistant to the disease with <10% dying, but 20-30% of children affected may die.

Medical and Physical Countermeasures.

Vaccination (Immunoprophylaxis)

Vaccines with providing limited protection are available to investigators in the United States. Approximately 20% of people do not respond to the DOD TC-83 vaccine that has IND (investigative new drug) status and about 20% require 1-2 days rest after vaccination. It is not effective against all serotypes of the virus. A formalin-inactivated form of TC-63 (C-84) can be use for those who do not respond to TC-83.

A vaccine may be available from the former Soviet Union.

 Specific Therapy

 No specific therapies are available.

Supportive care

 Symptoms are treated, e.g. with analgesics and anticonvulsants.

Decontamination

The virus is killed by common disinfectants, moist heat and drying. It can survive in dried blood and other secretions so care must be taken to decontaminate surfaces.

Agent Properties and Potential Uses

The virus is highly infective and a single particle may be enough to bring about disease. It is stable in aerosols and in body fluids. It is transmitted by many species of mosquitoes and this may give rise to the development of reservoirs of the virus in rodents and horses.

 The virus is also relatively easy to grow in cell culture and is robust enough to withstand storage and weaponization.

There are 11 subtypes of VEEV, of which three (IA, IB, and IC) can cause epidemics in man. The remainder survive without causing significant disease to their natural host: horses and their relatives.

Terrorist Acquisition and Attempted Use.

• None confirmed.