Western Equine Encephalitis Virus in South America

Level 4 - Avoid All Travel
Level 3 - Reconsider Nonessential Travel
Level 2 - Practice Enhanced Precautions
Level 1 - Practice Usual Precautions

Key points

  • There are reports of Western equine encephalitis virus (WEEV) infections in horses, humans or both, in parts of Argentina and Uruguay (see map).
  • WEEV is spread mostly by the bite of an infected mosquito and can cause severe disease.
  • Severe illness can occur in people of any age; however, young children, particularly infants and children aged <2 years, and older adults are at greater risk for severe illness.
  • Travelers to these areas should take steps to prevent mosquito bites.
  • Seek medical care immediately if you develop fever, headache, neck stiffness, photophobia (sensitivity to light), or confusion during or after travel and tell your healthcare professional you have been to an area with WEEV transmission.

Traveler Information

Clinician Information

Map of South America: Green indicates areas where WEEV infections have been reported in horses humans or both
Green indicates areas where WEEV infections have been reported in horses, humans or both (see larger map)
What is WEEV?

Western equine encephalitis virus (WEEV) is a virus most commonly spread to people through the bite of an infected mosquito. People most at risk for infection are those who are outdoors when mosquitoes are active.

Most people infected with WEEV do not feel sick or develop a mild febrile (fever) illness. However, the virus can cause some people to develop severe neurologic disease such as meningoencephalitis (inflammation of the brain and surrounding membranes) and myelitis (inflammation of the spinal cord). Symptoms of severe illness may include high fever, headache, neck stiffness, photophobia (sensitivity to light), confusion, somnolence (drowsiness), coma, or seizures.

There are no vaccines to prevent WEEV infection. The best way to prevent infection is to protect yourself from mosquito bites.