|
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."
|