“West Nile virus (WNV) is coming to a state near you if it hasn’t already arrived,” said Eileen Ostlund, DVM, PhD, head of the equine and ovine viruses section at the Diagnostic Virology Laboratory, National Veterinary Services Laboratory in Ames, Iowa, during the Western Veterinary Conference held February 15-19 in Las Vegas, Nev. In a comprehensive overview of WNV’s activity in the United States since its arrival in 1999, she discussed its transmission methods, hosts, U.S. history, clinical signs, diagnosis, vaccination options, impact on the U.S. horse population, duration of immunity, and supportive care.

Birds and Mosquitoes

Ostlund noted that WNV has been found in more than 130 bird species to date. “It’s not a picky virus in terms of its hosts,” she said. “No state lacks birds that can harbor WNV.”

Corvids (birds, including crows, bluejays, and magpies) have a high mortality rate when infected with WNV, she said, which has led to the recommendation that dead crows be tested for WNV in order to monitor the disease. However, she added that sparrows, finches, grackles, and some other species have a low mortality rate, but high viremia (a high level of virus in the bloodstream). Thus, even though you don’t see them dropping dead everywhere, they are significant reservoirs of the virus