Health officials charting the spread of West Nile virus across the United States project that "Texas and at least up to the Rocky Mountains will be affected" by the virus in 2002, said Dr. Kristen Bernard, assistant director of the Arbovirus Laboratories at the Wadsworth Center, New York State Department of Health. Bernard spoke during the Kentucky Thoroughbred Farm Managers' Club's meeting April 2 in Lexington.
More than one million doses of a West Nile vaccine developed by Fort Dodge Animal Health have been distributed as far west as California, which has not yet had a reported case of the virus. Fort Dodge is compiling data on the efficacy of the vaccine, which received its United States Department of Agriculture conditional license in August 2001, and is currently in phase three of safety and efficacy testing.
Early data is showing that at two to three weeks following a second application, the killed virus vaccine affords protection against the virus for eight months. Initial application should be followed by a first booster four weeks later, and subsequent boosters are recommended at six-month intervals. It is also recommended that horses be vaccinated prior to travel to states with virus.
Other preventive measures include mosquito control through insecticide use and eliminating standing water, including discarding of any possible water receptacles such as old tires. Carcasses of birds, particularly crows, which have died from an unknown cause, should be taken to a nearby testing lab, to test for West Nile virus. Disposable gloves and other protective clothing should be worn by anyone handling bird carcasses.
West Nile virus, which can also affect humans, is carried by birds and spread by mosquitoes. Signs of infection in horses include depression and lack of coordination, including rapid twitching of the muzzle and the muscles around the flank. While some mammals will not become diseased after being infected with the virus, horses can die from it.
Since it first appeared in New York in 1999, some kind of West Nile virus activity had showed up in 27 states by the end of 2001. With its spread has come a dramatic rise in the incidence of infection, and resulting fatality, in horses. In 1999, horses in the U.S. suffered a 28% fatality rate from 20 known cases; in 2000, there was a 38% fatality rate in 60 cases; and in 2001, there was a 24% fatality rate from an alarming 416 known cases.
Florida has accounted for 303 equine cases, by far the greatest number; the Maxwell H. Gluck Equine Research Center puts Kentucky's equine case total at eight. West Nile virus has been strongly concentrated throughout the South because that is the domain of the species of mosquito that spreads the disease to mammals.