Western equine encephalitis is an arboviral disease caused by western equine encephalitis virus, an alphavirus in the Togaviridae family. The virus is transmitted by mosquitoes and can affect the central nervous system in humans. [2][1]
Disease overview
Western equine encephalitis
西部马脑炎
Evidence-backed informationEN 6/7 applicable sections · ZH 6/7 applicable sectionsUpdated Sep 3, 2026
Western equine encephalitis is a relatively uncommon mosquito-borne viral disease caused by western equine encephalitis virus. Infection is often asymptomatic, but severe illness can involve encephalitis and lasting neurological effects. [1][2]
Read the full clinical and epidemiological profile7
The incubation period is reported as 5-10 days, and infection is frequently asymptomatic. Symptomatic illness may range from fever, chills, malaise, weakness, and myalgias to aseptic meningitis or encephalitis, including coma or death in severe cases. Long-term neurological effects may include fatigue, irritability, headache, and tremors. [2]
Recent increases in western equine encephalitis cases in South America have raised concern about the potential for endemic disease associated with adaptation to mosquito vectors. [1]
Western equine encephalitis virus is an arthropod-borne virus transmitted to people and horses through bites of infected mosquitoes, including mosquitoes in the Culex and Culiseta genera. Mosquito transmission occurs within a natural cycle involving birds, with transmission described during wet summer months. [2]
Young children, particularly those aged 2 years or younger, and adults older than 60 years are described as being at increased risk of more serious illness. Young children are more likely to experience permanent neurological disability, whereas mortality is more associated with older adults. [2]
The available evidence reports no effective vaccines for western equine encephalitis virus. [1]
- 1Wang L et al. Western equine encephalitis virus: A comprehensive review of epidemics, transmission, hosts, and strategies for mitigation. Virulence. 2025 Dec. PMID: 41178425. doi: 10.1080/21505594.2025.2580162.PubMed: https://pubmed.ncbi.nlm.nih.gov/41178425/
- 2Wikipedia contributors. Western equine encephalitis virus - Wikipedia [Internet]. Wikipedia. cited 11 Aug 2026.Available from: https://en.wikipedia.org/wiki/Western_equine_encephalitis_virus
- 3Martins MM et al. Arboviral diseases in pediatrics. J Pediatr (Rio J). 2020 Mar-Apr. PMID: 31605670. doi: 10.1016/j.jped.2019.08.005.PubMed: https://pubmed.ncbi.nlm.nih.gov/31605670/
- A83.1
- 1D46
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Recent related research
Vector competence of temperate and tropical mosquito species for Babanki virus
PLOS Neglected Tropical Diseases
Literature links are provided for discovery and do not alter or validate the surveillance series above.
Data access
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Official sourcesAuthority, cadence, notes1
JP NIID Weekly
Japan
Japan weekly infectious disease surveillance via NIID/JIHS.