10 Tips for reducing WNV risk

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10 TIPS FOR REDUCING YOUR HORSE'S WEST NILE RISK
Since first being recognized in the United States in 1999, West Nile virus (WNV)
has posed a serious threat to horses and humans alike. In the equine population,
the virus is transmitted when a mosquito takes a blood meal from a bird infected
with WNV, then feeds on a horse. While many horses exposed to WNV experience no
signs of illness, the virus can cause inflammation of the brain and spinal cord.
In some cases, especially in older horses, WNV can be fatal.
As a horse owner, prevention is the key to reducing your horse’s risk of
contracting WNV. Follow these guidelines from the American Association of Equine
Practitioners (AAEP) to protect your horse against WNV:
1. Consider vaccinating your horse against the disease. In February 2003, a
vaccine was licensed by the United States Department of Agriculture’s Center for
Veterinary Biologics for use in healthy horses as an aid in the prevention of
the disease. Talk with your veterinarian about the most appropriate vaccination
schedule for your horse.
2. Eliminate potential mosquito breeding sites. Dispose of old receptacles,
tires and containers and eliminate areas of standing water.
3. Thoroughly clean livestock watering troughs at least monthly.
4. 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.
5. Keep your horse indoors during the peak mosquito activity periods of dusk to
dawn.
6. Screen stalls if possible or at least install fans over your horse to help
deter mosquitoes.
7. Avoid turning on lights inside the stable during the evening or overnight.
8. Using insect repellants on your horse that are designed to repel mosquitoes
can help reduce the chance of being bitten.
9. Remove any birds, including chickens, located in or close to a stable.
10. 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.
For more information about the virus, ask your equine veterinarian for the “West
Nile Virus” brochure, produced by the AAEP in conjunction with Bayer Animal
Health, an AAEP Educational Partner. Additional information about WNV can be
found on the AAEP’s horse-health Web site, www.myHorseMatters.com.
The American Association of Equine Practitioners, headquartered in Lexington,
Ky., was founded in 1954 as a non-profit organization dedicated to the health
and welfare of the horse. Currently, AAEP reaches more than 5 million horse
owners through its 6,500 members worldwide and is actively involved in ethics
issues, practice management, research and continuing education in the equine
veterinary profession and horse industry.

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More WNV info:

West Nile Virus

Controlling the risk to your horse

How It Began


First isolated in Uganda in 1937, West Nile virus (WNV) is a virus that is transmitted principally by various species of mosquitoes and can cause inflammation of the brain and spinal cord (encephalomyelitis). Clinical disease caused by this virus is seen primarily in birds, equines and humans and very infrequently in goats, sheep, dogs, llamas, various reptiles and bears, among other species. Prior to its discovery in the northeastern U.S. in 1999, WNV was widely distributed in Africa, the Middle East, southwest Asia and parts of Europe.

††††††††††† West Nile virus was first recognized in the western hemisphere in September 1999, when it was isolated from the tissues of sick flamingoes and pheasants at the Bronx Zoo and from dead crows in the New York City area. By 2002 over 15,000 horses were diagnosed with West Nile Virus in 41 states.



Birds & Mosquitoes Play A Role In Transmission


††††††††††† Like Eastern and Western equine encephalomyelitis viruses, which historically have been identified with sleeping sickness in humans and equines in the U.S., WNV circulates in nature between birds and mosquitoes. Various species of birds serve as amplifying hosts of the virus, with at least 36 species of mosquitoes acting as vectors of WNV and transmitting it to a wide range of species. The strains of WNV present in North America are capable of causing disease in certain domestic and exotic species of birds, especially crows and blue jays, in which the infection is usually fatal. Humans, horses and a diversity of other mammalian species can also be infected with WNV. WNV infection in mammals does not result in large amounts of the virus in the bloodstream, as is seen in various bird species. This is important in terms of disease transmission. Because there is only a very small amount of the virus in the blood of infected horses, mosquitoes are unable to transmit the virus from horse to horse or from horse to human. The virus is transmitted when a mosquito takes a blood meal from an infected bird, then feeds on a horse. During the process of taking a blood meal from the horse, the virus is transmitted by the infected mosquito.



Clinical Signs


††††††††††† Horses and humans can become clinically affected by WNV. Typical of numerous other viral infections, many horses experience no clinical illness following exposure to the virus for the first time.

††††††††††† In horses infected with WNV, the virus may breach the blood-brain barrier and damage the brain and spinal cord. While the clinical signs of WNV encephalomyelitis can vary in range and severity, those most frequently observed include incoordination or ataxia (especially of the hind limbs); twitching of the muzzle and lower lip; and twitching of the muscles in the neck, shoulders or pectoral region. Signs may be bilateral or unilateral. Also reported are behavioral abnormalities (e.g., depression or heightened sensitivity to external stimuli, stumbling, toe dragging, leaning to one side and in severe cases, paralysis of the hindquarters, recumbency, coma and death. Other clinical signs that may be noted include fever, generalized weakness, impaired vision, inability to swallow, aimless wandering and convulsions. The nature and severity of clinical signs depend largely on the area(s) of the central nervous system affected by the virus and the extent of damage. The incidence of disease tends to be greater in older horses, where a favorable clinical outcome is less likely.

Diagnosis of WNV encephalomyelitis is usually based on the nature of the clinical signs displayed by an affected horse together with the detection of antibodies to the virus in the blood by laboratory examination. It is important to emphasize that many of the clinical signs of WNV encephalomyelitis closely resemble those observed in a number of other equine neurological diseases (e.g., Eastern equine encephalitis, rabies, equine protozoal myeloencephalitis, equine herpesvirus-1 and botulism) from which it must be distinguished.



Treatment


††††††††††† At the present time, there is no specific anti-viral treatment for WNV encephalomyelitis. Management should focus on controlling pain and inflammation. Anti-inflammatory drugs should be provided as soon as possible to control inflammatory changes in the central nervous system. Other supportive measures such as intravenous fluids, sedatives and nutritional support can be important components of therapy. It is important to consult your veterinarian immediately if you suspect your horse is affected with WNV encephalomyelitis so that the appropriate treatment measures can be implemented without delay.



Prevention


A number of measures can be taken to help protect your horse against WNV. These are comprised of management strategies to reduce exposure to mosquitoes and immunizing against the disease. Horses vaccinated against Eastern, Western or Venezuelan equine encephalomyelitis are not protected against WNV. In February 2003, a vaccine was licensed by the USDAís Center for Veterinary Biologics for use in healthy horses. The vaccine has been used extensively to prevent WNV infections in horses.

The vaccine should be administered as a series of two doses given three to six weeks apart. Foals should receive three immunizations starting at 6 months of age if the mare was immunized against WNV 30 days prior to foaling. The duration of immunity from vaccination is not known. It is recommended to vaccinate every four months in regions where the virus is active. Contact your veterinarian for the appropriate vaccination schedule for your location. In 2003, a recombinant canarypox vaccine was licensed for vaccination against WNV in horses. The vaccine has yet to be scrutinized in field conditions, but experimental studies reveal that it is protective against development of viremia involving WNV-infected mosquitoes.



††††††††††† Aside from vaccination against WNV, other measures should be taken to reduce the risk of your horse being bitten by a virus-infected mosquito. Concerted efforts should be made to eliminate or reduce potential mosquito breeding sites by disposing of old receptacles, tires and containers and eliminating areas of standing water on farms or at racetracks and wherever horses congregate.

Clean clogged roof gutters and turn over plastic wading pools or wheelbarrows when not in use. Thoroughly clean livestock watering troughs at least monthly. When it is not possible to eliminate particular breeding sites, measures should be taken to control mosquito populations through the selective use of larvicides and, under special circumstances, adulticides. Such action should only be taken, however, in consultation with your local mosquito control authority. If the application of such preparations is not advisable, use a species of fish that feed on mosquito larvae before they hatch. Keep horses indoors during peak mosquito activity periods (dusk to dawn). Screen stalls (if possible) or at least install fans over the horses to help deter mosquitoes. Avoid turning on lights inside the stable during the evening or overnight. Because mosquitoes are attracted to light, placing incandescent bulbs around the perimeter of the stable will attract mosquitoes away from the horses. Lights can also be used to draw mosquitoes to electric bug zappers.

The use of insect repellant that contain pyrethrin on horses can also reduce the chance of being bitten by mosquitoes. Remove any birds (including chickens) located in or close to a stable. Some veterinarians have success by hanging cattle ear tags on horse halters. These ear tags have been impregnated with insecticide and often reduce the effects of not only mosquito biting, but also midges and the effects of ìfly-strikeî dermatitis around the ears.

Because WNV can affect humans as well as horses, donít forget to take actions to protect yourself as well. When outdoors in the evening, wear clothing that covers your skin and apply plenty of mosquito repellent.



Conclusion


††††††††††† You as a horse owner need to become well-informed of the potential consequences of infection with this virus, as with all diseases, and take appropriate measures to reduce the risk of transmission of WNV to your horse(s). Prevention is key to the control of this infection. You should consult your local veterinarian on how best to protect your horse(s) against this disease.



For more information, contact your veterinarian.
American Association of Equine Practitioners (AAEP)
4075 Iron Works Parkway
Lexington, KY 40511

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Also

Is WNV Vaccine Safe in Pregnant Mares?
by Written by Dr. Tom Lenz, AAEP 2003 President (source: Courtesy of American Quarter Horse Journal )
Recently, rumors have been circulating around the horse community that the West Nile Virus Vaccine is causing abortions in pregnant mares and birth defects in foals. The rumors began on May 30, 2003, when the Denver Post newspaper published an article entitled “West Nile Vaccine Eyed in Foal Losses.” On June 16, 2003, the Post published another article entitled, “Vet Wants Warnings on W. Nile Vaccines: Some Blame Shot for Horse Illnesses.” The author of both articles assigned a causal relationship between the use of West Nile virus (WNV) vaccine and subsequent abortions in pregnant mares and newborn foal birth defects. The articles were based on claims from some Midwestern horse breeders that their mares had aborted or produced deformed foals soon after vaccination with the WNV vaccine. Unfortunately, the articles were sensational and compelling to many broodmare owners despite the fact that much of the information was speculative and not based on scientific fact. Despite the misleading information, the rumors are flying and many broodmare owners, including some of my clients, are afraid to vaccinate their mares.


I’ve visited with representatives from Ft. Dodge Laboratories, the manufacturer of the WNV vaccine; the USDA Center for Veterinary Biologicals, that approves and oversees equine vaccines; and various veterinary diagnostic laboratories around the country and none are seeing scientific proof that the vaccine is causing a problem. Because West Nile virus affected nearly 15,000 horses across the country in 2002 with roughly 30% of the infected, nonvaccinated horses dying, the decision to not vaccinate your horses is a very serious one.


Let’s look at the facts. We know that normally roughly 10-15% of mares diagnosed pregnant during the first month of their pregnancy will resorb or abort sometime during that pregnancy. Most are due to uterine incompatibility, low progesterone levels, stress, inadequate nutrition, or genetic defects in the embryonic vesicle. We also know that a number of infectious agents, including Herpes Virus (Rhino), Equine Viral Arteritis, Equine Infectious Anemia (EIA), and bacterial infections, do cause abortions in all stages of pregnancy. We also know that mares carrying twins and those on fescue pastures are prone to late term abortions. Birth defects can be genetically induced or due to toxins or hormones in feed or weeds. We know that over 7 million doses of the WNV vaccine have been administered over the last few years and the company that produces the vaccine has reported that they have received roughly 3.3 reports of pregnancy loss per million doses used. Keep in mind that the West Nile virus vaccine is a killed virus vaccine, which means that the virus has been killed prior to being placed in the vaccine. Historically, killed vaccines are extremely safe and are not prone to produce adverse reactions. USDA’s Center for Veterinary Biologicals confirmed that to date, they have received only a very small number of reports regarding a possible association between the use of West Nile virus vaccine and abortions, birth defects, or other reproductive anomalies or failures. They have also reiterated that the vaccine is safe and effective. Veterinary diagnostic laboratory representatives have also stated that neither a veterinarian or diagnostic laboratory examined the aborting mares or deformed foal that started this entire issue. Unfortunately, the specific cause of their problem will never be known.


In making the decision to use any vaccine or medical therapy it is important to weigh the pros and cons of its ultimate benefit to the horse. But that decision must be based on scientific fact, not rumors or emotions. And remember that if your mare aborts or produces a stillborn or deformed foal, have your local veterinarian examine them immediately to determine the cause of the problem.


Until I see documented, scientific evidence that the West Nile virus vaccine is causing problems, I will continue to use it and recommend its use to my clients. I know that without its protection, horses will contract the disease and at least 30% of them will die. I also encourage horse owners and veterinarians with questions regarding West Nile virus vaccine and their pregnant mares or adverse reactions following use of the vaccine to contact the USDA’s Animal and Plant Inspection Service Center for Veterinary Biologicals at (800) 752-6255 or via their website at www.aphis.usda.gov/vs/cvb.