Vaccination and internal parasite control are integral components of equine preventive healthcare programs. The American Association of Equine Practitioners recommends that all horses be vaccinated with core vaccines against tetanus, rabies, Eastern and Western equine encephalitis, and West Nile virus infection regardless of age, use, or geographic region. For internal parasite control in adult horses, the current recommendation is targeted treatment of horses identified by fecal egg count as high shedders. A targeted anthelmintic therapy approach reduces parasite contamination of pastures while slowing development of anthelmintic resistance that can result from overuse of deworming medications.<\/p>\n
Take-Home Points<\/strong><\/p>\n <\/div><\/div><\/p>\n Throughout the United States, routine vaccination and internal parasite control are key components of preventive healthcare programs for horses. Core vaccines prevent life-threatening diseases with potential to affect all horses regardless of age, region, or use; risk-based vaccines target contagious diseases that can cause illness and affect performance in certain populations of horses. Vaccination and deworming programs are ideally overseen by a veterinarian and are often done in concert with other key parts of an annual wellness program that includes routine physical examination, dentistry, and husbandry consultation. Although this article focuses exclusively on vaccination and internal parasite control, veterinarians are <\/span>encouraged to engage clients in multifaceted preventive care programs that promote the overall health and longevity of their patients.<\/span><\/p>\n The American Association of Equine Practitioners (AAEP)<\/a> recommends that all horses be vaccinated with core vaccines against tetanus, encephalomyelitis, rabies, and West Nile virus infection (<\/span>TABLE 1<\/b><\/span>).1<\/sup> Vaccination with risk-based vaccines depends on a horse\u2019s risk for acquiring the disease, being affected by the disease, and spreading the infection. Further information and detailed vaccine recommendations can be found at the AAEP Vaccine Guidelines<\/a>.1<\/sup><\/span><\/p>\n A \u201cone-size-fits-all\u201d vaccination program for adult horses does not exist. In addition to the core vaccines, risk-based vaccines are selected according to a horse\u2019s likelihood of contracting a particular disease and should be evaluated against the risks and cost of vaccination. Regional disease prevalence can drive risk-based vaccination recommendations, as can travel plans and intended use of the horse. <\/span><\/p>\n Currently, U.S. Food and Drug Administration (FDA)\u2013approved equine vaccines are available to prevent tetanus, encephalomyelitis (Eastern, Western, and Venezuelan equine encephalitis viruses), West Nile virus infection, rabies, rhinopneumonitis (equine herpesvirus [EHV] types 1 and 4), influenza, strangles (Streptococcus equi <\/i>subspecies equi<\/i>), Potomac horse fever, botulism, equine viral arteritis, anthrax, leptospirosis, snake envenomation, and rotavirus infection. Most vaccines are administered via the intramuscular route; intramuscular and intranasal vaccines are available for influenza, EHV infection, and strangles.1<\/sup><\/span><\/p>\n As for other species, horses require a primary vaccine series (generally 2 to 3 doses administered 4 to 5 weeks apart) to achieve a protective immune response. Maximum immunity is generally achieved 1 to 2 weeks after vaccine series completion. The primary series is routinely administered to horses in the first year of life but can also be administered to adult horses with unknown vaccine history. After receiving the initial vaccine series, most horses will require annual or semiannual booster vaccinations. In the southeastern United States, where mosquito vectors are present year-round, boosters for insect-borne arboviral diseases may be administered more frequently.<\/span><\/p>\n Minimal research has been conducted to establish protective antibody titers<\/a> or other measurements that could be used to dictate frequency of revaccination of horses. Given the current attention in small animal practice to lengthening revaccination intervals for adults, clients may ask their equine veterinarians for this information. Titer testing is also frequently requested by owners of horses known to react to vaccination. At this time, no evidence supports lengthening vaccine intervals for the horse, and doing so may leave the animal at risk for serious diseases. For horses with serious, life-threatening reactions to vaccination, veterinarians are encouraged to consult the AAEP Guidelines for Serology in Horses with Adverse Events from Vaccination<\/a>.2<\/sup><\/span><\/p>\n Broodmares require specific vaccines during gestation to prevent abortion and provide antibody-rich colostrum to the newborn foal. Vaccine protocols for pregnant mares use killed vaccine products and generally include vaccination against EHV-1 and EHV-4 at gestation months 5, 7, and 9 as well as a single booster for all core and risk-based vaccines 4 to 6\u00a0weeks before foaling, which prevents EHV-associated abortion and promotes high concentrations of antibodies in colostrum.1<\/sup><\/span><\/p>\n Foals born to properly vaccinated mares that receive adequate colostrum (as determined by routine blood immunoglobulin G concentration testing at 24 hours of age) should begin the primary vaccination series at<\/span> 6<\/span>\u00a0<\/span>months of age to ensure timely protection for the foal, while allowing adequate time for clearance of maternal antibodies from the foal\u2019s bloodstream.1<\/sup> Maternal antibodies are protective in the first few months of life but can also interfere with the foal\u2019s immune response to vaccines. If a mare was not vaccinated 4 to 6 weeks before foaling or if the foal did not receive colostrum, the vaccination series should begin when foals are 3 to 4 months of age.1<\/sup><\/span><\/p>\n Tetanus<\/b><\/p>\n Tetanus <\/b>is caused by a potent neurotoxin derived from anaerobic, spore-forming bacteria<\/span> (Clostridium<\/i><\/span> <\/i>tetani<\/i>)<\/span> that<\/span> live<\/span> in<\/span> the<\/span> soil<\/span> and<\/span> can<\/span> be<\/span> found<\/span> in<\/span> the<\/span> intestinal<\/span> tract<\/span> and<\/span> feces<\/span> of horses. C<\/i><\/span> <\/i>tetani<\/i><\/span> <\/i>spores <\/span>survive<\/span> in<\/span> the<\/span> environment<\/span> for<\/span> many<\/span> years,<\/span> resulting<\/span> in<\/span> an<\/span> ever-present risk for exposure of horses and humans on equine facilities. Horses are at risk of contracting<\/span> tetanus<\/span> if<\/span> they receive<\/span> a<\/span> laceration<\/span> at<\/span> any<\/span> location (e.g., a<\/span> puncture<\/span> wound<\/span> to the<\/span> foot)<\/span> or<\/span> any<\/span> surgical procedure<\/span> (e.g., castration).<\/span> Foals that failed to acquire immunity through passive transfer are at increased risk of contracting tetanus via the umbilicus. Also at risk are postpartum mares after dystocia or with retained fetal membranes. <\/span>The<\/span> neurotoxin<\/span> causes<\/span> progressive muscle rigidity and spasticity (\u201clock jaw\u201d) that can result in recumbency and death. Mortality can be as high as 80% in affected horses.3 <\/sup>Tetanus can be prevented by an annual<\/span> vaccination with tetanus toxoid.3<\/sup><\/span><\/p>\n If a horse becomes injured and has not received a tetanus toxoid vaccine in the previous 6 months, a booster is recommended at the time of injury.3<\/sup> If a horse has never received a tetanus toxoid vaccine and sustains an injury, vaccination with tetanus antitoxin is necessary.3<\/sup> Tetanus antitoxin induces immediate passive protection that lasts approximately 3 weeks. Historically, tetanus antitoxin was associated with Theiler\u2019s disease (hepatic disease and often failure). Recently, this syndrome has been attributed to equine parvovirus contained in equine biological products, and all FDA-licensed equine biological products are now tested for equine parvovirus before distribution.<\/span><\/p>\n Encephalomyelitis<\/b><\/p>\n Eastern<\/span> equine encephalitis (EEE) and Western equine encephalitis (WEE) are insect-transmitted viral diseases that affect the central nervous system, resulting in lethargy,<\/span> ataxia,<\/span> blindness,<\/span> recumbency,<\/span> and<\/span> seizures. The disease caused by these viruses is colloquially referred to as \u201csleeping sickness\u201d because of the initial lethargy, depression, inappetence, and fever. For all of the encephalitides, the virus exists in bird and rodent reservoirs and is transmitted by mosquitoes. Although incidence of disease is low, mortality rates can be high; mortality rates for EEE approach 90% to 95%.4 <\/sup> The mortality rate for WEE is significantly less (around 30%), and very few cases have been reported in Florida.4<\/sup> An additional encephalitis virus, Venezuelan equine encephalitis (VEE), occurs in South and Central America, is considered a risk-based vaccine, and is included in some of the multivalent equine encephalitis virus vaccines. Recent VEE activity in Mexico has increased the risk for horses residing along the southern U.S. border, and VEE vaccination of horses residing in these geographic regions is recommended.<\/span><\/p>\n West Nile Virus<\/b><\/p>\n West Nile virus, a mosquito-transmitted neurologic pathogen, emerged in the United States in 1999 and is now considered endemic to the United States. West Nile virus infection is not as lethal as EEE, but infected horses may require several days of hospitalization and intensive care to survive. The mortality rate for horses infected with West Nile virus is approximately 32% to 35%, and some recovered horses experience long-term neurologic deficits.5<\/sup><\/span><\/p>\n Rabies<\/b><\/p>\n Rabies<\/span> is<\/span> an infrequent but<\/span> fatal<\/span> zoonotic <\/span>neurologic<\/span> disease<\/span> that affects <\/span>all mammals, including humans. Rabies virus is transmitted through the saliva<\/span> of<\/span> infected animals.<\/span> Common wildlife reservoirs for rabies virus include raccoons, skunks, bats, and foxes.<\/span> Although<\/span> the<\/span> incidence<\/span> of<\/span> rabies<\/span> in horses <\/span>is<\/span> low,<\/span> it<\/span> is<\/span> a<\/span> serious public<\/span> health<\/span> concern<\/span> due to <\/span>the potential for a rabid animal to infect its human caregivers. Thus, vaccination of horses is prudent not only<\/span> for<\/span> the<\/span> health<\/span> of<\/span> the<\/span> horse<\/span> but also<\/span> for <\/span>the<\/span> safety<\/span> of<\/span> people<\/span> working<\/span> with<\/span> the<\/span> horse.<\/span> All horses should be vaccinated for rabies annually.1<\/sup> Although the label instructions for foals do not recommend a booster for the primary series, it is prudent to consider doing so due to the difficulty of predicting the end of maternal antibody interference.<\/span> For adult horses receiving the rabies vaccine for the first time, no primary series booster is required; only annual boosters are needed. There is no evidence to support that the vaccination interval can be lengthened (as it can be for small animals).<\/span><\/p>\n\n
Vaccination<\/h2>\n
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<\/a><\/p>\nYearlings Through Adults<\/h3>\n
Broodmares and Foals<\/h3>\n
Equine Core Vaccines<\/h3>\n
Risk-Based Vaccines<\/h3>\n
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