Chikungunya disease: This disease is an acute febrile illness followed by more chronic polyarthritis. It is transmitted by Aedes mosquitoes and is common in Africa, India, Guam, Southeast Asia, New Guinea, and limited areas of Europe. Prevention involves avoiding mosquito bites.

Mayaro disease: This dengue-like disease is transmitted by mosquitoes. It is common in Brazil, Bolivia, and Trinidad. Prevention involves avoiding mosquito bites.

Tick-borne encephalitis: Initially, a mild flu-like illness occurs, accompanied by leukocytopenia and thrombocytopenia, which clears up within a few days. About 30% of patients develop more severe symptoms (eg, meningitis, meningoencephalitis). A vaccine is available in Europe and Russia.

California encephalitis: This encephalitis and related infections are transmitted by mosquitoes and occur in the US Midwest and probably worldwide. This infection causes symptoms (eg, fever, somnolence, obtundation, focal neurologic findings, seizures) primarily in children. Temporal lobe involvement may mimic herpes encephalitis; 20% of patients develop behavioral problems or recurrent seizures. Mortality rate is < 1%. No treatment is available.

Omsk hemorrhagic fever and Kyasanur Forest disease: These infections are transmitted by ticks or by direct contact with an infected animal (eg, rodent, monkey). Omsk hemorrhagic fever occurs in the former Soviet Union, including Siberia; Kyasanur Forest disease occurs in India. They are acute febrile illnesses accompanied by bleeding diathesis, low BP, leukopenia, and thrombocytopenia; some patients develop encephalitis in the 3rd wk. Mortality rate is < 3% for Omsk hemorrhagic fever and 3 to 5% for Kyasanur Forest disease. Prevention involves avoiding tick bites and infected animals.

Rift Valley fever: This infection is spread by mosquitoes and transmitted by direct or indirect contact with the blood or organs of infected animals (eg, during slaughtering, butchering, or veterinary procedures), inhalation of infected aerosols, or ingestion of raw milk from infected animals. Rift Valley fever occurs in South Africa, eastern Africa, and Egypt. Rarely, it progresses to ocular disorders, meningoencephalitis, or a hemorrhagic form (which has a 50% mortality rate). A vaccine for livestock is available, and a human vaccine is under investigation.

Last full review/revision December 2009 by Kenneth M. Kaye, MD

Content last modified February 2012