(USA) (Tahyna virus [Europe]) A mild, febrile, viral disease which occasionally causes severe encephalitis. It is transmitted by mosquitoes from small wild mammals, mainly in summer, to persons frequenting woodland areas of the USA and Canada, and certain European countries such as Yugoslavia and the USSR. The causative agents are the California encephalitis group of viruses (Bunyaviridae). There is no vaccine.

RESERVOIR AND MODE OF TRANSMISSION:

The virus cycles amongst small wild animals (e. chipmunks, squirrels, rabbits and hares) and a variety of mosquito species. The infection can be maintained independently over several years by transovarial transmission in the mosquito. Humans are accidental hosts infected by mosquito bite during occupational or recreational activities in wooded areas. Accidental infections from laboratory accidents have occurred.

INCUBATION PERIOD:

Humans. 5-15 days. Animals. Unknown.

CLINICAL FEATURES:

Humans. Symptoms lasting about 5-10 days range from fever and headache with nausea and vomiting to fits and signs of aseptic meningitis, encephalitis and neurological sequelae. Animals. Unknown but assumed subclinical.

PATHOLOGY:

Humans. Encephalitis. Animals. Unknown.

DIAGNOSIS:

Humans. The virus may sometimes be isolated from blood or rarely, from cerebrospinal fluid. Serologic tests of blood or cerebrospinal fluid may be diagnostic in specific types of encephalitis (by demonstrating virus-specific IgM or a fourfold change in complement-fixing or neutralizing antibodies).
Animals. Impracticable.

PROGNOSIS:

Humans. In humans, fatality is rare but neurological defects may persist.
Animals. Thought to be subclinical.

PREVENTION:

Humans. Prevent mosquito bites. Control the mosquito vector. Apply laboratory safety procedures. Animals. Impracticable.

TREATMENT:

Humans. Vigorous symptomatic therapy. Such measures include reduction of intracranial pressure (Mannitol), monitoring of intraventricular pressure, the control of convulsions, maintenance of the airway, administration of oxygen, and attention to adequate nutrition during periods of prolonged coma.
Animals. Not applicable.