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La Crosse Encephalitis Virus in the USA (Ohio)

28 Jul 2017

A second case of La Crosse encephalitis was reported in central Ohio on 24 July 2017. Local health officials are implementing mosquito control measures and providing informationt to the public.

La Crosse encephalitis virus is transmitted to humans through the bite of an infected mosquito. Most cases occur in the mid-west, mid-Atlantic and southeastern USA.Symptoms include fatigue, fever, headache, nausea and vomiting. Encephalitis can occur in serious cases, most commonly in children. Death can occur, although this is rare.

There is no specific treatment for La Crosse encephalitis virus and no vaccine is available. Prevention is by avoiding mosquito bites.

Advice to Travellers

Avoidance of mosquito bites should always be considered as the first line of defence against mosquito-borne infection, especially malaria, dengue fever, chikungunya, zika and yellow fever.

Different species of mosquito bite at different times of day, and transmit different infection so prevention measures are advisable at all times.


  • Anopheles mosquitoes which spread malaria tend to bite between dusk until dawn.
    • Peak biting activity occurs around midnight in those mosquitoes that spread malaria in Africa. In South America and South East Asia the mosquitoes tend to bite in the evening.
  • Aedes mosquitoes that transmit dengue, chikungunya, zika and yellow fever tend to bite between dawn and dusk.

For further advice see Mosquito Bite Avoidance.