As of Sept. 4, 2012, West Nile virus (WNV) infections in people, animals, or mosquitoes have been reported from all states except Alaska and Hawaii, according to the Centers for Disease Control and Prevention (CDC). Of 1,993 human cases, 54% involved the nervous system. When are mosquitoes especially active? Dawn and dusk. When are most horse people also active? Dawn and dusk. If WNV is reported from 48 states, people and horses in 48 states are at-risk of being bitten by infected mosquitoes.

The only U.S.-approved WNV vaccines are for horses, and the American Association of Equine Practitioners lists WNV as a core vaccine, emphasizing its importance. Compare the cost for WNV vaccination versus costs for veterinary examination, diagnosis, and treatment of a neurological horse. And, let’s not forget that any neurological horse needs to be handled as a rabies-suspect until proven otherwise.

While extensive WNV data is available at the CDC ArboNet website, equine specific data is not. According to the Kentucky State Veterinarian’s website, as of Sept. 11, 2012, 10 WNV-positive horses were reported from nine counties. Seven horses were unvaccinated; two were partially vaccinated, and one was reportedly vaccinated. A summary of Kentucky WNV equine cases (2005- 2011) shows that 91% of positive horses were not vaccinated; others were partially vaccinated or had unknown vaccination history. How complete is your equine vaccination program?

Understanding WNV vectors is important to human and equine health. Mosquitoes in the genus Culex are primary vectors of WNV with multiple species being able to transmit the virus throughout the continental United States. The house mosquito (Cx. pipiens complex) is common in areas across Kentucky. Inseminated females spend the winter in protected places near a moisture source and mortality is usually low following mild winters. Surviving females become active, laying rafts of eggs on the surface of water with moderately to very high organic content including grassy ditches, waste lagoons, and polluted ground pools. The life cycle from egg to adult takes about eight to 12 days during the summer