Veterinarians across the country seem to agree that the equine industry needs better vaccines and improved education of horse owners regarding vaccinations.
Vaccine Wish List
D. Craig Barnett, DVM, would like to see vaccinations against Lyme disease, Clostridial diseases, Rhodococcus equi, salmonella, and leptospirosis.
Dr. Barnett is senior equine technical services veterinarian with Intervet/ Schering-Plough Animal Health in Paola, Kan. He is on the American Assn. of Equine Practitioners’ Infectious Disease Committee and helped write the group’s current vaccination guidelines.
Barnett also is hoping for a safer and more efficacious strangles vaccine as well as an updated, more efficacious Potomac horse fever vaccine.
“The challenge is making vaccines that are both efficacious and safe,” he says. “Manufacturers also have to see a return on investment because of the significant research and development cost required to bring a new vaccine to the market.
“Examples of improvement and advances in innovative vaccine technology,” he says, “are well represented by Flu Avert IN (Intervet’s intranasal modified live influenza vaccine) and PreveNile (Intervet’s West Nile vaccine, live flavivirus chimera).
“Both vaccines,” he says, “require only one dose for primary immunization, both have an excellent safety profile, a rapid onset of immunity and a long-lasting duration of immunity, all supported by an extensive amount of referenced, challenged data.”
Barnett says the PreveNile chimeric technology is very new and innovated technology acquired from Acambis, a company with expertise in discovering, developing and manufacturing human vaccines.
“The Potomac horse fever vaccine was created from the original strain,” says Judy Marteniuk, DVM, MS. “Now, PHF is found in 46 of the 48 states. There are many different strains and we need more efficacious vaccines.”
Dr. Marteniuk, associate professor of equine medicine and extension at Michigan State University’s College of Veterinary Medicine, says she watches a new vaccine for about six months before using it on her horses or recommending it to clients. “I want to make sure it is safe as well as efficacious,” she says.
Another example is equine protozoal myeloencephalitis, the degenerative neurological disease diagnosed in horses for more than 30 years. An experimental EPM vaccine was marketed for a time, but clinical studies have not produced enough efficacy for the vaccine’s continued production, she says.
“No vaccine provides 100 percent efficacy,” she notes.
Behind the Scenes
Drug companies are hard at work improving their products, Marteniuk says.
“Hundreds of thousands of dollars (or more) are spent bringing one product to market,” she says. “Most products have been in the research pipeline for 10 to 15 years before coming available.”
The American Assn. of Equine Practitioners recommends that all horses be given these core vaccines: Eastern and Western equine encephalomyelitis, tetanus, West Nile and rabies. Administration frequency is listed in the AAEP’s newest vaccination guidelines, available at AAEP.org, which were written by the group’s Infectious Disease Committee.
Risk-based vaccination recommendations include equine influenza, equine herpes virus, botulism, anthrax, Potomac horse fever, strangles, rotoviral diarrhea and equine viral arteritis.
“If the disease can kill the horse, it should be vaccinated against it,” Marteniuk said. “Strangles, herpes (rhino) and flu cause sickness but not usually death. Evaluate the risk of giving the vaccine versus not vaccinating at all.”
AAEP guidelines recommend veterinary consultation in creating a vaccination schedule, but owners seem to be increasingly doing vaccinations themselves.
Marteniuk reminds practitioners to share with clients the dangers of giving the vaccinations themselves just to save the cost of a vet call. “Tell them what can happen if they give the vaccines at the wrong time of year—encephalitis vaccinations given in the fall in Northern aspects of the country do not provide adequate protection when needed. Or, if given in the wrong part of the body, intranasal vaccine given intramuscularly can create abscesses.
“Perhaps veterinarians might educate owners through newsletters, emphasizing the importance of timing for insect population and other risk factors,” she says. “Owners should know that they must vaccinate at least 10 to 14 days before a show or they will have an animal with a potential sore neck and no protection against disease.”
Having a veterinarian administer vaccines gives the horse owner another advantage, Marteniuk says. The practitioner will perform a physical exam at the same time, often observing clinical signs that owners and barn managers don’t notice.
Should owners insist on administering a vaccine, April Knudson, DVM, urges that veterinarians teach proper handling of the vaccines and which diseases to vaccinate against.
Dr. Knudson is an equine specialist with Merial Ltd.’s Large Animal Veterinary Services. Merial is based in Duluth, Ga.
Knudson emphasizes the importance of vaccinating any horses that travel. “Performance animals should definitely be current on their flu and rhino vaccines,” she says.
Merial’s Recombitek technology has resulted in two vaccines: an annual one for West Nile and another for equine influenza.
Knudson says the Recombitek vaccines act as modified live vaccines with the safety of killed vaccines. “There is zero chance of the vaccine reverting back to virulence and making the animal sick,” she says.
Rabies and Botulism
Rabies is found nationwide because equine housing is easily accessible to wildlife, Knudson says. Merial’s equine Potomavac + IMRAB vaccinates for both Potomac horse fever and rabies in one shot.
Leslie Easterwood, DVM, says rabies is a high risk in Texas. Veterinarians in that part of the U.S. also vaccinate against Venezuelan equine encephalitis or encephalomyelitis.
Dr. Easterwood, a medical lecturer in the College of Veterinary Medicine at Texas A&M University, has seen a decrease in the number of vaccinations administered by veterinarians she works with. She hopes there is at least a rise in the mail-order vaccine business.
“I’d rather see horse owners go that route than not vaccinate at all, trying to save money,” she says. “Even if a horse is in a closed population, it is still exposed to insects and wildlife. Horses have no innate immunity.”
Jennifer Newman, DVM, MS, is concerned that botulism occurs so sporadically and unpredictably that veterinarians may not recognize it soon enough in an affected horse.
Dr. Newman is a technical service veterinarian with Neogen Corp., which makes BotVax B, the only USDA-
approved vaccine for equine botulism caused by Clostridium botulinum type B. The company’s Animal Safety Division is located in Lexington, Ky.
Botulism is caused by a neurotoxin produced by a soil-borne, spore-forming bacterium, Clostridium botulinum. Horses are affected by types A, B and C and show signs of weakness, poor tongue tone, dysphagia, recumbency and eventual flaccid paralysis.
“Diagnostic testing takes too long to produce a definitive diagnosis,” she says. “By the time botulism is confirmed, which is not always possible, affected horses are already undergoing intensive care and supportive therapies.”
She says horses with mild to moderate cases of botulism often recover, though the patients are subject to complications from being recumbent too long.
“Vaccinating is much less expensive than treating a horse after it becomes intoxicated,” Newman says. “Even with the best intentions, many affected horses cannot be saved.”
The Different Types
Newman says types A and C bacteria tend to dwell in soil west of the Mississippi River. Type B is found on the Eastern Seaboard, in the Mid-Atlantic states and in the Ohio Valley.
But the toxin is not limited to these areas. An outbreak last year in Ocala, Fla., killed about 120 horses. The cause was suspected to be botulinum toxin haylage, which may have grown in soil contaminated with C. botulinum.
“Horses in non-endemic areas may encounter C. botulinum spores in hay originating from endemic states,” Newman says. Because of drought or economic conditions, hay could be shipped from those areas. Hay cubes, round bales and haylage have been linked to botulism because of improper processing or contamination by dead rodents.
This article first appeared in the August 2009 issue of Veterinary Practice News.