New Mexico's Pet Resource SPRING 2004


AN OUNCE OF PREVENTION: What You Need To Know About
West Nile Virus & Your Pets

By Deborah Schildkraut, Ph.D.

Over the past few years, West Nile Virus (WNV) has spread rapidly across the United States. It is now found throughout New Mexico, infecting both humans and horses. According to the USDA’s Animal & Plant Health Inspection Service (APHIS), there were 4,636 cases of WNV in horses in the United States in 2003. APHIS’ 2003 statistics show New Mexico had the third highest number of cases in the U.S. with 420 confirmed horses with WNV.

The terrible course of the disease in an infected horse was chronicled in Kazan’s Journey Back in the Winter 2004 issue of PETroglyphs. Kazan’s case clearly demonstrates why preventative measures are well worth your time and effort.

West Nile Virus is transmitted when a mosquito carrying the virus bites a horse or person. Birds are the host species for WNV. The virus lives and grows in the bird, sometimes killing it, but more often causing mild or no illness. The bird then develops immunity to the disease. Mosquitoes are the vectors for the disease. They bite infected birds, sucking in the virus with the blood. The mosquitoes do not become ill from the virus. Instead, the virus is stored in the salivary glands of the insect. When a mosquito carrying the virus bites an animal, the virus is transmitted via the saliva to that animal through the bite. What is known about the disease and the way in which it affects our pets?


The Center for Disease Control web site reports that few cases of WNV have been documented in dogs and cats. When they have been infected with the disease, the resulting illness is rarely severe. Currently there is no vaccine available for dogs and cats. Veterinarian Dr. Robert Gruda of Santa Fe reports that he has not seen any cases in dogs or cats in his practice. He feels that the greater threat to dogs from mosquitoes is heartworm, not WNV.


West Nile Virus can cause severe illness or death in horses. The infection comes within a few days or up to 15 days after being bitten by a WNV-carrying mosquito. This can happen at any time during mosquito season. Initially an infected horse may go off feed, and then begin to show signs of ataxia, or walking funny, especially in the back end. If symptoms appear, a vet should be called immediately. A test done on a sample of the horse’s blood will verify if the illness is WNV, rather than some other neurological ailment. Currently, treatment consists of efforts to abate the symptoms. Your vet may use banamine, which is a pain reliever, and other anti-inflammatory drugs to combat the symptoms. As with most viruses, there is no drug for curing WNV. The horse can struggle and suffer extensively with the disease. The process of treating an infected horse can run up large medical bills. Many horses die. Prevention is a far better route to take in dealing with WNV.


Fortunately there is a WNV vaccine available for horses. The first time a horse is vaccinated against WNV, two injections are necessary. After the initial injection, a second booster shot follows three to six weeks later. To be most effective in guarding the horse against WNV, the vaccine protocol should be completed by mid-spring. After the first year, a single annual booster is required for protection. In New Mexico, some vets recommend an additional booster in August.

Maintaining your horse in general good health is important. According to veterinarian Dr. Leslie Adler of Madrid, NM, a well fed and parasite-free animal with a strong immune system is less susceptible and has an easier time dealing with infections. She suggests using a topical insect repellant that is safe for horses, a good one that will keep insects away for several hours. There are also horse sheets, lightweight coats that prevent fly and mosquito bites. If you are in a heavily infested mosquito area, a sheet may be a worthwhile investment. The American Veterinary Medical Association has more information on their web site, including a Spanish version, at: AVMA.

Do take measures to reduce the mosquito population around your home and barn. Treat the area where your horses live with the same care that you take around your own home. For example, remove all standing water, which is where mosquitoes breed. For more information on reducing the mosquitoes around your home, yard and barn, please visit the Fight the Bite web page of the federal Center for Disease Control at: Fight the Bite.

For most of us, our animal companions are an important part of our lives. We do not want to see them suffer needlessly. Whether the toll is measured in medical bills, pain & suffering, or loss of life, in the case of the West Nile Virus, an ounce of prevent is invaluable.

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