Review highlights similarities in West Nile Virus infections in horses and humans

The manifestation of neuroinvasive disease from West Nile Virus in horses and humans is remarkably similar, according to the authors of a just-published review.

Neurological disease from West Nile Virus (WNV) infection threatens the health and well-being of horses and humans worldwide, Erika Schwarz and Maureen Long wrote in the journal Viruses.

Before its emergence in North America, West Nile virus generally caused a febrile syndrome referred to as West Nile fever, with limited outbreaks of neuroinvasive disease in Africa and hotspots of activity in the Mediterranean and Eastern European countries.

Since the explosive emergence of the mosquito-borne disease in North America, humans and horses are at risk for developing serious diseases worldwide, they said.

Before its encroachment in North America, outbreaks of WNV neuroinvasive disease in humans or horses were becoming more frequent, as reported in North Africa, France, Romania, and Russia in the late 1990s, the authors noted.

Neuroinvasive disease is estimated to occur in 0.66 to 1% of symptomatic human patients. In horses, approximations vary slightly, but it is estimated that between 10% and 20% of exposed horses develop neuroinvasive disease.

The drivers of risk for both humans and horses are similar.

In both species, virus dynamics within the host are similar, as is the evolution of the antibody response. The signs, symptoms and pathology are, likewise, similar.

In their review, Schwarz, with the Montana Veterinary Diagnostic Laboratory, and Long, with the College of Veterinary Medicine at the University of Florida, set out to compare WNV infection in humans and horses and to identify similarities that can be exploited to enhance surveillance methods for the early detection of the neuroinvasive form of the disease.

The authors traversed the factors that influenced outbreaks, features of virus transmission, and the nature of the infection in both humans and horses.

Both species, they said, undergo cyclic outbreaks of febrile neurological disease that tend to overlap both geographically and in terms of time.

“These similarities can be exploited to leverage and improve surveillance for the detection of WNV outbreaks,” they said.

Surveillance of neuroinvasive disease in horses and mortality events in birds can point to the increased risk posed by the virus to humans.

“Exploiting the similarities in neuroinvasive symptoms in humans and horses can enhance the specificity of syndromic surveillance strategies.”

Syndromic surveillance is a strategy for the identification of general health abnormalities not dependent on diagnostic testing to serve as an early warning system for disease threats.

“Further harmonization of ancillary testing methods across regions and countries will also result in more accurate and timely detection of WNV outbreaks.”

Schwarz, E.R.; Long, M.T. Comparison of West Nile Virus Disease in Humans and Horses: Exploiting Similarities for Enhancing Syndromic Surveillance. Viruses 2023, 15, 1230. https://doi.org/10.3390/v15061230

The review, published under a Creative Commons License, can be read here.