Venezuelan equine encephalitis

Venezuelan equine encephalitis is a vector-borne viral disease caused by Venezuelan equine encephalitis virus, a mosquito-borne pathogen that can affect all equine species as well as humans ^[1]. The disease manifests as encephalitis or encephalomyelitis in susceptible hosts ^[1]. Six subtypes (I–VI) have been identified through serological testing, with subtypes I variants A, B, and C representing the primary epizootic strains ^[1].

In equines, infection may result in sudden death or progressive central nervous system disorders affecting horses, donkeys, and zebras ^[1]. Human infection in healthy adults typically presents with flu-like symptoms including high fevers and headaches ^[1]. Severe illness and mortality are more common in individuals with weakened immune systems, young children, and the elderly ^[1].

Since its first isolation in 1938, Venezuelan equine encephalitis has caused 21 reported outbreaks in the Americas, including in Mexico, Colombia, Venezuela, and the United States ^[1]. Outbreaks typically occur following periods of heavy precipitation that promote mosquito population growth ^[1]. A documented outbreak in Trujillo, Venezuela (December 1992–January 1993) resulted in 28 cases with 12 deaths ^[1]. Enzootic subtypes remain localized to endemic areas and generally do not affect equine populations, while epizootic subtypes spread rapidly and are highly pathogenic to horses ^[1].

Venezuelan equine encephalitis is transmitted by Culex mosquitoes, which acquire the virus by feeding on infected animals and subsequently transmit it to other animals or humans ^[1]. Enzootic transmission cycles involve rodents as reservoir hosts, while epizootic cycles feature equine animals as the primary amplifying hosts, which develop high viremia levels sufficient to infect feeding mosquitoes ^[1]. Other mammals including cattle, swine, and dogs can become infected but generally do not play significant roles in transmission ^[1]. The emergence and geographic spread of VEE, along with other arboviral diseases, has been facilitated by increased air travel and uncontrolled mosquito vector populations ^[2].

Prevention of Venezuelan equine encephalitis focuses on controlling mosquito vector populations and preventing mosquito bites ^[2]. The emergence of VEE and similar arboviruses through secondary amplification in domesticated animals underscores the importance of animal health surveillance as part of prevention strategies ^[2]. No specific antiviral treatment is available, making vector control the primary public health intervention ^[2].

1. 1Wikipedia contributors. Venezuelan equine encephalitis virus - Wikipedia [Internet]. Wikipedia. cited 4 Sept 2026.Available from: https://en.wikipedia.org/wiki/Venezuelan_equine_encephalitis_virus
2. 2Weaver SC et al. Zika, Chikungunya, and Other Emerging Vector-Borne Viral Diseases. Annu Rev Med. 2018 Jan 29. PMID: 28846489. doi: 10.1146/annurev-med-050715-105122.PubMed: https://pubmed.ncbi.nlm.nih.gov/28846489/