Kyasanur Forest disease (KFD) is a tick-borne viral hemorrhagic fever of the Flaviviridae family. The disease in endemic to the Kyasanur Forest of southwestern India in the state of Karnataka (formerly Mysore). Locally it is referred to as monkey disease. About 500 cases per year are reported in this area.

Naturally acquired KFD presents with initial symptoms that include the sudden onset of severe fever, chills, headache, severe prostration, arthralgia, generalized lymphadenopathy, myalgia, jaundice, and facial flushing. Petechiae may also be noted. After 72 hours, 40% of patients may develop diarrhea and vomiting in addition to hemorrhaging from the nose, gums, and intestines. Ocular manifestations include conjunctivitis and photophobia. The soft palate typically has vesicles. The initial phase lasts 6-11 days, after which the patient may have an afebrile period of 1-3 weeks followed by development of central nervous system involvement including confusion, delirium, seizures, and coma.

The incubation period of KFD is 2-9 days. There are no known cases of person-to-person transmission; however, transmission via exposure to infected body fluids and inhalation of infectious aerosol has been documented. Since the virus can be isolated from blood during the first 12 days of illness, protective measures should be taken to avoid exposure.

The mortality rate of KFD is 5%-10%. A tick-borne encephalitis vaccine is available in Russia but has not been approved in the United States.