Eastern Equine Encephalitis Virus

Eastern Equine Encephalitis Virus (EEEV) is a mosquito-borne pathogen and notorious agent of brain inflammation and death in horses and humans. First isolated in 1933, it has been tracked in the northeastern and southeastern United States with a predominance in the New England states and Florida. While most infected individuals will remain asymptomatic or develop a mild fever, roughly 5% will develop neuroinvasion and encephalitis. Those who develop neurological disease have a case-fatality rate of 30-70%, the most severe of all arthropod-borne encephalopathies (e.g., Venezuelian Equine Encephalitis, St. Louis Encephalitis, and LaCrosse Encephalitis). EEEV was responsible for 110 confirmed neuroinvasive cases from 2011-2020 [CDC]. 


Most exposed to EEEV will remain asymptomatic, although patients older than 50 and younger than 15 are more susceptible to symptomatic infection [CDC]. Symptoms are often flu-like, such as fever and headache 4-10 days after infection. If the virus infiltrates the brain, massive inflammation and swelling of neural tissue can occur, called encephalitis [Steele & Twenhafel, 2010]. Encephalitis can display as confusion, paralysis, seizures, and eventually coma and death. There is no cure for EEEV encephalitis, and patients typically remain on supportive care until death or subsidence of symptoms.


In 2019, there were 38 confirmed EEEV neuroinvasive cases across multiple states, an increase from the previous annual averages by 5- to 9-fold [CDC]. Though a vaccine has been created and recommended for horses, there has been no licensed human vaccine for this virus [Armstrong & Andreadis, 2022; Mundis et al, 2022]. The severe fatality rate and potential to be aerosolized has additionally marked it as a potential agent of bioterrorism [Steele & Twenhafel, 2010] .


The disease pathogenesis of EEEV is currently being investigated in multiple animal models, including non-human primates. Multiple vaccines are also being studied, though the rarity and sporadic nature of the disease makes proficient funding scarce [Morens et al., 2019]. Sentinel animals, particularly chickens, have been a significant source of data for researchers to track this pathogen in Florida and create models to predict and prevent future outbreaks.



Philip M Armstrong, Theodore G Andreadis, Ecology and Epidemiology of Eastern Equine Encephalitis Virus in the Northeastern United States: An Historical Perspective, Journal of Medical Entomology, Volume 59, Issue 1, January 2022, Pages 1–13, https://doi.org/10.1093/jme/tjab077

Centers for Disease Control and Prevention (2022). Eastern Equine Encephalitis Virus. Retrieved from https://www.cdc.gov/easternequineencephalitis/index.html.

Morens, D. M., Folkers, G. K., & Fauci, A. S. (2019). Eastern equine encephalitis virus — another emergent arbovirus in the united states. The New England Journal of Medicine, 381(21), 1989-1992. doi:https://doi.org/10.1056/NEJMp1914328

Stephanie J Mundis, Steve Harrison, Dave Pelley, Susan Durand, Sadie J Ryan, Spatiotemporal Environmental Drivers of Eastern Equine Encephalitis Virus in Central Florida: Towards a Predictive Model for a Lethal Disease, Journal of Medical Entomology, Volume 59, Issue 5, September 2022, Pages 1805–1816, https://doi-org.libux.utmb.edu/10.1093/jme/tjac113

K. Steele, N. Twenhafel, REVIEW PAPER: Pathology of Animal Models of Alphavirus Encephalitis, American College of Veterinary Pathologists, Volume 47, Issue 5, June 15, 2010 https://doi-org.libux.utmb.edu/10.1177/0300985810372508

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