West Nile fever is a disease caused by a viral infection. For the first time the virus of the West Nile fever was isolated in 1937 in Uganda. The disease is spread mostly in Africa and Asia.
The incubation period ranges from several days to 2-3 weeks but usually it is 3-6 days. The disease starts sharply with the rapid increase in body temperature to 38-40°C and is accompanied by a fever. In some patients, the rise of body temperature is preceded by such short-term symptoms as general weakness, loss of appetite, fatigue, feeling of tension in the muscles, sweating and headache. Febrile period lasts for 5-7 days on average, although it may be shortened to 1-2 days.