In a recently published study Texas A&M University veterinarians identified two “hot spots” of West Nile virus (WNV) based on data they collected between 2002 and 2004. One of these spots is in northwestern Texas and the other in an eastern region of the state. Mapping areas in which WNV is concentrated enables veterinarians to institute disease control and prevention programs via targeted surveillance and owner education.

West Nile virus was first introduced into North America in New York in 1999 and rapidly spread across the continent in a southwestern direction. WNV is maintained through a mosquito-bird cycle. Horses bitten by infected mosquitoes may show no signs of disease, have a mild illness, or in some cases, develop a fatal neurological disease.

“Since WNV is spread by mosquitoes, environmental factors are thought to be important in determining where WNV infections are likely to occur,” explained Michael Ward, BVSc, MPVM, PhD, formerly of the department of Veterinary Integrative Biosciences at Texas A&M (Ward is currently the Sesquicentennial Chair in the department of Veterinary Public Health and Food Safety at the University of Sydney in Australia).

The northwestern “hot spot” included six counties (Cochran, Hockley, Lubbock, Terry, Lynn, and Garza), while the eastern “hot spot” included four counties (Freestone, Limestone, Leon, and Robertson).

In 2002 and 2003 veterinarians reported a relatively even distribution of horses with WNV in all areas of the state. In 2004 most of the horses diagnosed were in the southeastern portion, indicating the virus was moving in that direction from the north and west.

“It is anticipated that these study results will facilitate the institution of targeted disease prevention strategies to minimize the number of horses infected with WNV,” summarized Ward.

Further research to determine why the virus is concentrated in these areas is ongoing.

The study, “Identification of hyperendemic foci of horses with West Nile virus disease in Texas,” was published in the March 2008 edition of the American Journal of Veterinary Research