West Nile Virus on the Move

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Reports of West Nile Virus causing human health problems have hit the news lately with Texas considering some widespread spraying to halt the spread of disease in people. Where there are human cases, there will be many more equine cases since this is a mosquito spread disease. Luckily horses do have safe and efficacious vaccines for WNV.

Amy Glaser, DVM PhD, senior research associate at the Animal Health Diagnostic Center at Cornell University?s College of Veterinary Medicine, emphasizes the problem. ?This year has seen an elevated level of West Nile Virus activity in many geographic areas, including parts of the Northeast, Midwest and Texas. We all need to be aware of the presence of the virus and to take measures to avoid or prevent mosquito exposure. Horses should be vaccinated for West Nile virus and for Eastern Equine Encephalitis virus.?

Many horse owners may have felt the drought would slow down mosquito-borne viruses, but this is not the case. Horses who have never received a WNV vaccine should get two doses given two weeks apart. You can assume you have good protection by about 10 days after the second dose. Horses who are receiving a booster dose generally have renewed immunity within a few days after their booster. Foals whose dams were vaccinated should get their initial series at four to six months of age.

The WNV protection can be achieved by using a single vaccine if your horse is already up to date on other vaccines or more commonly, as part of one of the combo vaccines. If you prefer to spread your horse's vaccines out over the year, June or July is an ideal time to give a WNV/EEE (Eastern Equine Encephalitis) combo vaccine. It is not too late to protect your horses now however. Both WNV and EEE are on the move and mosquito season is far from over.

In addition to vaccinating, try to avoid having your horses outside at the prime mosquito feeding times of dawn and dusk. Use a fly spray that also repels mosquitoes. Encourage birds that eat mosquitoes such as barn swallows and even hummingbirds. Dump water troughs and tanks every other day even with the drought to prevent larval development. You can also seed ponds with larval eating fish, dragonfly larvae and BTI or Bacillus thuringiensis israelensis ? a bacteria that kills mosquito larvae.

- Deb Eldredge, DVM, Horse Journal Contributing Veterinary Editor