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Northwest Iowa Dairy Outlooks

A local discussion of current science and issues concerning dairying in northwest iowa

I have had several calls this week about protecting horses from West Nile Virus. Since first being recognized in the United States in 1999, West Nile virus (WNV) has posed a serious threat to horses and humans alike notes veterinarians from the American Association of Equine Practitioners. In the equine population, the virus is transmitted when a mosquito takes a blood meal from a bird infected with WNV, and then feeds on a horse.

In horses, the disease can cause acute, fatal neurologic disease affecting the brain and spinal cord. However, clinical disease does not always occur. Horses may show signs of stumbling, weakness and rear limb incoordination. Mildly affected horses can recover in two to seven days. Horses that survive appear to recover fully.

The disease can be diagnosed through a blood sample.

However, even in areas where the disease is known to exist, less than one percent of mosquitoes are infected, and less than one percent of the people bitten by an infected mosquito become infected.

Historically, West Nile virus seems to recur around the world on about a 10-year cycle.

As a horse owner, prevention is the key to reducing your horse’s risk of contracting WNV. The first step is to vaccinate your horse against the disease with one of the available vaccines. The first time horses are vaccinated for West Nile virus, they need two doses of vaccine separated by a period of three to six weeks. A booster dose is needed every year. Horses aren’t fully protected until three to four weeks after the second dose.

Follow these guidelines to help protect your horse against WNV:

1. Eliminate potential mosquito breeding sites. Dispose of old receptacles, tires and containers and eliminate areas of standing water.

2. Thoroughly clean livestock watering troughs at least weekly.

3. Use larvicides to control mosquito populations when it is not possible to eliminate particular breeding sites. Such action should only be taken, however, in consultation with your local mosquito control authority.

4. Keep your horse indoors during the peak mosquito activity periods of dusk to dawn.

5. Screen stalls if possible or at least install fans over your horse to help deter mosquitoes.

6. Avoid turning on lights inside the stable during the evening or overnight.

7. Using insect repellants on your horse that contain DEET and are designed to repel mosquitoes can help reduce the chance of being bitten.

8. Remove any birds, including chickens, located in or close to a stable.

9. Don’t forget to protect yourself as well. When outdoors in the evening, wear clothing that covers your skin and apply plenty of mosquito repellent.

Many veterinarians recommend vaccinating animals against Eastern equine encephalitis and Western equine encephalitis if horses aren’t already protected. However, EEE, WEE, and VEE belong to another family of viruses for which there is no cross-protection.

West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus. Normal veterinary infection control precautions should be followed when caring for a horse suspected to have this or any viral infection.Also, there is no documented evidence that West Nile virus is transmitted between horses. We do not know if an infected horse can be infectious (i.e., cause mosquitoes feeding on it to become infected). However, previously published data suggest that the virus is detectable in the blood for only a few days.


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