Equine veterinarian Rob Keene, DVM, believes that controlling travel is paramount in limiting diseases that spread from horse to horse.
For horses transported routinely across town or across the nation, he says, non-core vaccinations make a lot of sense.
“Significant disease outbreaks occur in environments where horses are very mobile,” says Dr. Keene, an equine professional services veterinarian for Boehringer Ingelheim Vetmedica Inc. of St. Joseph, Mo. “Increasing the number of horse-to-horse contacts will increase the chances of disease transmission of many respiratory viruses.”
Keene, who has served on committees of the American Association of Equine Practitioners, says the most important tools are sometimes the simplest.
“An example would be to quickly identify febrile or anorexic horses so that adjacent individuals can be monitored,” he says. “Establishing a quarantine strategy for new arrivals to a population can also be helpful.”
The AAEP’s list of risk-based, or non-core, vaccines includes those for anthrax, botulism, equine herpes virus (rhinopneumonia), equine viral arteritis, equine influenza, Potomac Horse Fever, rotaviral diarrhea and strangles.
Recommended protocols, available at AAEP.org, take into account a horse’s age, breed, use, general health, environment and exposure to disease—factors in the risk of infection.
April L. Knudson, DVM, large-animal veterinary services manager at Merial Ltd. of Duluth, Ga., says a horse’s travel schedule needs to be taken into consideration when deciding on vaccines. She says horses that travel can easily spread disease and should be vaccinated according to protocols for the particular geographic area.
“Flu, for example, is spread from horse to horse via aerosolized virus particles and direct nose-to-nose contact with infected horses or virus-contaminated people or fomites,” Dr. Knutson says.
The AAEP recommends that all horses be vaccinated against equine influenza unless they live in a closed, isolated facility. The virus doesn’t constantly circulate, even in large herds, but it can be sporadically introduced by an infected horse.
Experts say newly arriving horses should be quarantined for at least 14 days. Ideally, horses should be vaccinated before any exposure. In addition, horses at risk of exposure should be vaccinated every six months; annual vaccinations are recommended for horses with less risk.
Performance or show horses in high-risk areas may require more frequent vaccinations for equine herpes virus or rhinopneumonitis.
Potomac Horse Fever, or equine monocytic ehrlichiosis, originally was considered a sporadic disease affecting horses in the Eastern U.S. near the Potomac River. The disease has since been found in other regions of the U.S. and in Canada.
If Potomac Horse Fever occurs on a farm, additional cases are likely in future years, research shows. The vaccination should be administered every six to 12 months, according to manufacturers’ instructions, beginning with foals at 5 months old. Horses in endemic areas may be vaccinated every three or four months.
Good hygiene and sanitation are important with strangles, which is transmitted by direct contact with infected horses, subclinical shedders or indirect contact with feeding and watering equipment, grooming equipment, humans and insects. Exposing water and equipment to direct sunlight and using disinfectants are important to reduce the spread of infection.
Work With Clients
Julia H.Wilson, DVM, Dipl. ACVIM, who served on the AAEP’s Infectious Disease Committee, says she knows of horse owners in the Midwest who administer vaccines themselves to save the cost of a veterinary call. Some skip non-core vaccines entirely if they think the risk of infection is low.
Forgoing risk-based vaccines is not a good idea, all three veterinarians agree.
In this economy, Knudson says, horse owners “might be tempted to skip some vaccinations to save some money.”
“But,” she says, “this could end up costing more money in the long run if the animal should get sick.”
Keene says vaccines are basic to equine health. The focus at Boehringer Ingelheim Vetmedica, he says, “is on supporting and selling our biologics to licensed practicing veterinarians with a doctor-patient-client relationship.”
Wilson, an associate professor of large animal medicine at the University of Minnesota, recommends that veterinarians hand out the AAEP’s vaccination guidelines to educate clients about maintaining their horses’ health.
Educating clients not only can improve a horse’s health but also prove profitable for the equine practitioner.
“Seminars are good ways to speak to large numbers of horse owners at the same time,” Knudson says. “Advertising the educational seminar in local horse magazines or the newspaper could be a way to attract new clients who may not be vaccinating their horses.”
Keene says many professional or technical services vetertinarians spend a lot of time supporting the veterinarians through client seminars.
“These are important tools to provide the message to our clients regarding routine veterinary care and selection of the appropriate vaccine programs,” he says.“Fostering good client education through health care programs offered through the practice and periodic newsletters can be very important in increasing client compliance in a tough economy.”
After the Vaccine
Knudson says adverse reactions to vaccines are rare but should be reported to the manufacturer. If multiple vaccines from multiple manufacturers were administered simultaneously, the reaction should be reported to all the manufacturers.
The AAEP’s non-core vaccination guidelines warn about “a significantly increased risk of adverse reactions to the strangles vaccine in exposed horses. All injectable, inactivated S. equi vaccines, particularly the whole-cell bacterin, are associated with an increased rate of injection site reactions as compared to other equine vaccines.”
An intranasal vaccine, with pharyngeal and lingual tonsils as the inductive sites, has been shown to stimulate a high level of immunity to strangles, the AAEP says. Of course, accurate delivery is critical to a vaccine’s efficacy. Veterinarians should administer all parenteral vaccines before the adminstration of the intranasal S. equi vaccine.
“It is important that any unexpected or adverse reactions from biologics be reported to the company,” Keene says. “All legitimate animal health companies have the moral and regulatory obligation to track the products they sell so that any issues can be identified quickly and investigated. “Many states have reporting requirements that are established by the office of the state veterinarian. That office can be a big help to disseminate that information.”
State and federal animal officials can help veterinarians stay in compliance with control programs for equine viral arteritis. According to the AAEP, though outbreaks are infrequent, the number of confirmed cases of EVA seems to be increasing because of increased global movement of horses, accessibility of carrier stallions and shipments of cooled or frozen virus-infected semen.
Stallions and mares to be exported should be tested and confirmed negative for antibodies before vaccination, experts say.
For anthrax and botulism, the AAEP recommends that vaccines be given annually to horses pastured in endemic areas.
Another disease, rotavirus, is a major cause of foal diarrhea. Morbidity can be as high as 50 percent, with less than 1 percent mortality with veterinary intervention.
Vaccinating mares results in a significant increase in foals’ rotavirus antibody titers. Field trials of rotavirus vaccination in pregnant mares have shown a decrease in the incidence and severity of foal diarrhea on farms that have had annual rotaviral cases. Other studies have shown the rotavirus antibody in vaccinated mares’ colostrum.
Risk-based vaccines certainly don’t cover all infectious equine diseases.
“There is considerable research at both at the veterinary colleges and the pharmaceutical companies,” says Wilson, “in making effective vaccines for diseases for which we are already vaccinating, such as EHV1, and for diseases against which we do not currently have a vaccine, such as EIA.”
Keene says commercial and university research programs are looking at all equine infectious diseases that are difficult to manage, are expensive to treat or are life-threatening.
Knudson would like to see a vaccine for Rhodoccochus equi, which is especially dangerous to young foals.
Along with a vaccine for R. equi, Keene hopes researchers will develop better methods to control salmonella, Clostridial diseases and pigeon fever, or Corynebecterium pseudotuberculosis.
Wilson would like to see new vaccines for equine infectious anemia, lepto, Lyme disease, anaplasmosis, Clostridial enteritis and salmonella.