Severe flu-like illness lasting for about 4 days; About 1% of patients develop complications (ocular, meningoencephalitis, or hemorrhagic liver failure. [CCDM, p. 521]
Initial symptoms are a flu-like illness with arthralgias, lower backache, photophobia, and headache. Two severe complications that occur in about 1% of cases are encephalitis and hemorrhagic fever. Hemiparesis and coma occur in encephalitis. The hemorrhagic fever is associated with hepatitis, jaundice, hemorrhages, and renal failure. Another complication is retinitis. [Guerrant, p. 464] Complications of this mosquito-borne viral infection include encephalitis, hepatitis, and hemorrhages. Fever may be biphasic. [CCDM, p. 521] Retinal vasculitis occurs in about 10% of patients with otherwise mild infections and can result in visual impairment. [Harrison, p. 726]
Sheep and other domestic ruminants (sheep, goat, cattle, camels) are reservoirs. Workers may be infected handling tissues of animals (necropsy or butchering), and aerosols have transmitted infection in the laboratory. The case-fatality rate is 1-5% but can be as high as 50% in hospitalized patients. [CCDM, p. 521-2] It is possible that transmission occurs by ingestion of raw milk. [www.who.int/mediacentre/factsheets] Domestic ungulates such as sheep and cattle serve as amplifiers during epidemics. [PPID, p. 2026] Travelers to endemic areas should avoid mosquito bites and contact with livestock. An investigational vaccine has not been approved by the FDA. [CDC Travel, p. 350-1] Hemorrhagic fever occurs in less than 1% of patients and typically about 1-2 weeks after a wave of spontaneous abortions in livestock. An outbreak in Egypt in 1977-1978 (200,000 patients and 600 deaths) was associated with movement of camels from Sudan. [Cecil, p. 2158-9] Vaccination of livestock can prevent epidemics. [Harrison ID, p. 1046]
For updated text and symptoms of infectious diseases, see iddx.com.