Western equine encephalitis is a viral disease caused by western equine encephalitis virus, an alphavirus within the Togaviridae family, and is classified among the arboviral encephalomyelitis-producing infections [2][3]. It is a mosquito-borne zoonotic agent historically studied in reptiles as part of arbovirus surveillance and challenge research [3].
Disease overview
Evidence-backed information EN 5/7 applicable sections · ZH 5/7 applicable sections Updated Oct 23, 2026
Western equine encephalitis is a re-emerging alphavirus infection transmitted by mosquitoes that has shown rising case numbers in South America, raising concern about endemic establishment through vector adaptation [1][2]. No effective vaccines or specific treatments are currently available for human infection [1]. The disease can cause severe central nervous system injury and long-term neurological consequences in affected individuals [1][2].
Read the full clinical and epidemiological profile 6
Alphavirus infections tend to induce clinical disease characterized by rash, arthralgia, and arthritis, as seen with chikungunya virus, Ross River virus, and Semliki Forest virus, or encephalomyelitis, as seen with eastern equine encephalitis virus, western equine encephalitis virus, and Venezuelan equine encephalitis virus [2]. Some patients who recover from the initial acute illness may develop long-term sequelae regardless of the specific infecting virus [2].
Recent increases in western equine encephalitis cases have been reported in South America, with concern that viral adaptation to mosquito vectors could enable endemic persistence [1]. Decades ago, reptiles were surveyed and challenged with western equine encephalitis virus in studies of arbovirus zoonotic potential [3].
Western equine encephalitis virus is maintained in a natural mosquito-borne transmission cycle and is transmitted to humans through infected mosquito vectors [1][2]. Alphaviruses including this agent are spread via mosquitoes whose ranges are expanding geographically [2]. Reptiles have been examined in challenge trials as part of understanding the virus's zoonotic and reservoir potential [3].
No effective vaccines or treatments for western equine encephalitis virus are currently available, though biochemical products are under investigation in animal models [1]. Defensive strategies against the virus remain focused on research priorities such as vector understanding and development of countermeasures rather than deployed interventions [1].
- 1 Wang 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/
- 2 Baxter VK et al. Genetic control of alphavirus pathogenesis. Mamm Genome. 2018 Aug. PMID: 30151711. doi: 10.1007/s00335-018-9776-1. PubMed: https://pubmed.ncbi.nlm.nih.gov/30151711/
- 3 Ariel E et al. Viruses in reptiles. Vet Res. 2011 Sep 21. PMID: 21933449. doi: 10.1186/1297-9716-42-100. PubMed: https://pubmed.ncbi.nlm.nih.gov/21933449/
- A83.1
- 1D46
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Weather factors in the prediction of western equine encephalitis epidemics in Manitoba
Epidemiology and Infection
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