West Nile Virus Risk Factors Identified

A variety of environmental factors might be related to West Nile virus infections.

A variety of environmental factors might be related to West Nile virus infections in horses, reported a Florida research team lead by Leslie M.V. Rios, PhD, from the Department of Entomology and Nematology at the University of Florida in Gainesville.

West Nile virus (WNV) is a threat to horses and humans in North America, including the state of Florida where 1,082 equine cases of WNV were reported between 2001 and 2006.

"Florida plays an important role in the equine industry; many breeding horses are located with the state and are at risk of infection even with the availability of three commercially licensed vaccines," wrote the researchers.

To assess risk factors of WNV in Florida horses, Rios and colleagues reviewed data collected from horses tested for the disease in 2001, 2002, and 2003. Their hypothesis was that "increased risk factors for WNV transmission to horses are related to the availability of mosquito larval habitat, animal housing conditions, and animal management practices."

Key findings of the study included:

  • The WNV vaccine was highly protective;
  • Quarter Horses were most commonly affected;
  • Natural water on farm property was protective, and
  • Factors increasing the risk of WNV were use of fans, and housing in stables constructed of solid wood or cement.

The study also showed that dead birds or other ill animals on the property were risk indicators for disease. Further research regarding the use of fans, insecticides, and canopy cover is needed.

The researchers recommended testing all unvaccinated horses that show clinical signs of WNV infection between June and November. Horses that show clinical signs of WNV infection within one month or more than six months after vaccination should also be tested.

The study, "Environmental risk factors associated with West Nile virus clinical disease in Florida horses," was published in the December 2009 edition of the journal Medical and Veterinary Entomology. The abstract is available on PubMed.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.