IAMAT |International Association of Medical Assistance to Travellers| IAMAT |International Association of Medical Assistance to Travellers|

Viral Encephalitis

Photo By: Carol Scott

Viral Encephalitis is a symptom caused by arthropod-borne viruses also known as arboviruses. These viruses, belonging to the Togaviridae, Flaviviridae, and Bunyaviridae families, are zoonoses – animal infections that can spread to humans – that are transmitted by mosquitoes, ticks, moth flies, and sand flies who feed on mammals and birds. Humans become ill when they get bitten by infected insects since the viruses target the Central Nervous System. Arboviruses are not transmitted from person to person.

Venezuelan Equine Encephalitis (VEE), Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), St. Louis Encephalitis (SLE), and La Crosse Encephalitis (LAC) are illnesses caused by infected mosquitoes while Powassan Encephalitis (POW) is caused by ticks.

>> Travel health advice for similar arboviral illnesses: Japanese Encephalitis, Tick-Borne Encephalitis, and West Nile Virus


Arboviruses are found worldwide and the transmission period is seasonal, typically from spring to fall. Travellers involved in outdoor activities such as hiking, camping, ecotourism, and agricultural work are at risk. Persons with a weakened immune system, children, and older persons are more susceptible to developing the infection.


Most infections are asymptomatic – persons do not exhibit symptoms. Those who get ill, typically present with flu-like symptoms including fever, headache, muscle pain, chills, nausea, vomiting, and general weakness within days of being exposed to the virus. In some patients, neurological symptoms can develop including confusion, convulsions, drowsiness, and behavioural changes. The illnesses can progress to inflammation of the brain, respiratory system disorders, coma, and sometimes death. Treatment includes supportive care of symptoms.


Travellers should take measures to prevent mosquito and tick bites. There is no vaccine or preventive medication against Viral Encephalitis.

Mosquito and tick bite prevention:

More on tick bite prevention:

More details on insect bite prevention.

Information last updated: January 2020

Travel Health Journal