Everglades virus: an underrecognized subtype of Venezuelan equine virus

Information about the severity of this new sub-type encephalitis virus and the susceptibility of vaccinated horses seems to be unavailable. However, I would expect horses vaccinated with the current trivalent killed virus products to get protection.
DrO

Everglades virus: an underrecognized disease-causing subtype of Venezuelan equine encephalitis virus endemic to Florida, USA
J Med Entomol. 2023 Nov 14;60(6):1149-1164. doi: 10.1093/jme/tjad070.
Authors
Nathan D Burkett-Cadena 1 , Durland Fish 2 , Scott Weaver 3 , Amy Y Vittor 4
Affiliations

1 Florida Medical Entomology Laboratory, University of Florida Institute of Food and Agricultural Sciences, 200 9th St. SE, Vero Beach, FL 32962, USA.
2 Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA.
3 Department of Pathology, Center for Biodefense and Emerging Infectious Disease, University of Texas Medical Branch, Galveston, TX 77555-0609, USA.
4 Department of Medicine & Emerging Pathogens Institute, University of Florida, Gainesville, FL 32611, USA.

PMID: 37862065
PMCID: PMC10645373
DOI: 10.1093/jme/tjad070

Free PMC article
Abstract

Everglades virus (EVEV) is subtype II of the Venezuelan equine encephalitis virus (VEEV) complex (Togaviridae: Alphavirus), endemic to Florida, USA. EVEV belongs to a clade that includes both enzootic and epizootic/epidemic VEEV subtypes. Like other enzootic VEEV subtypes, muroid rodents are important vertebrate hosts for EVEV and certain mosquitoes are important vectors. The hispid cotton rat Sigmodon hispidus and cotton mouse Peromyscus gossypinus are important EVEV hosts, based on natural infection (virus isolation and high seropositivity), host competence (experimental infections), and frequency of contact with the vector. The mosquito Culex (Melanoconion) cecedei is the only confirmed vector of EVEV based upon high natural infection rates, efficient vector competence, and frequent feeding upon muroid rodents. Human disease attributed to EVEV is considered rare. However, cases of meningitis and encephalitis are recorded from multiple sites, separated by 250 km or more. Phylogenetic analyses indicate that EVEV is evolving, possibly due to changes in the mammal community. Mutations in the EVEV genome are of concern, given that epidemic strains of VEEV (subtypes IAB and IC) are derived from enzootic subtype ID, the closest genetic relative of EVEV. Should epizootic mutations arise in EVEV, the abundance of Aedes taeniorhynchus and other epizootic VEEV vectors in southern Florida provides a conducive environment for widespread transmission. Other factors that will likely influence the distribution and frequency of EVEV transmission include the establishment of Culex panocossa in Florida, Everglades restoration, mammal community decline due to the Burmese python, land use alteration by humans, and climate change.

Keywords: Everglades virus; Spissipes; alphavirus; arbovirus.

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