Number of West Nile Virus Cases Continues to Grow

Every state in the 48 contiguous United States has now experienced a taste of West Nile virus since it first was detected in the Western Hemisphere in 1999.

Having their first encounters with West Nile virus this year were Nevada (found in birds, mosquitoes, horses, and humans) and Oregon (in birds and horses).

By Aug. 26, the USDA had reported 351 equine cases in 28 states. The three states with the most equine cases were Arizona, California, and Wyoming. California's equine cases have steadily risen -- West Nile virus was confirmed in 158 horses by Aug. 26, and 82 of those died or were euthanized. Another 51 cases were pending confirmation. Arizona had logged 67 equine cases by Aug. 30, and 27 Wyoming cases were reported.

Veterinarians still hold that mosquito-source reduction and vaccination are an owner's best bets for preventing the virus. There are two equine vaccines, each of which requires an initial series of vaccinations followed by boosters given periodically.

Meanwhile, by Sept. 1, mosquito season was well under way and Eastern equine encephalitis had reared its head in several states, with cases reported in Alabama, Delaware, Florida, New Jersey, New York, Texas, and Virginia.

Last year was an epidemic year for Florida (207 cases in 50 counties), but 2004 has been an average EEE year, with 29 cases from 19 counties by Sept. 1. Again, mosquito eradication and vaccination measures are recommended for protecting horses against the disease.