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Professional Version

Vaccination Program for Horses

By

Allison J. Stewart

, BVSc (Hons), PhD, DACVIM-LAIM, DACVECC, School of Veterinary Science, University of Queensland

Medically Reviewed Oct 2022 | Modified Nov 2022

The goal of vaccination is to develop and maintain both individual and herd immunity against infectious diseases. Commercial vaccines are available for rabies Rabies Rabies is an acute, progressive encephalomyelitis caused by lyssaviruses. It occurs worldwide in mammals, with dogs, bats, and wild carnivores the principle reservoirs. Typical signs include... read more , encephalomyelitis Meningitis, Encephalitis, and Encephalomyelitis in Animals Meningitis, encephalitis, and encephalomyelitis are terms used to describe inflammatory conditions of the meninges, brain, or brain and spinal cord, respectively. These inflammatory processes... read more Meningitis, Encephalitis, and Encephalomyelitis in Animals (Eastern, Western, and Venezuelan), tetanus Tetanus in Animals read more , influenza Equine Influenza Equine influenza is highly contagious and spreads rapidly among naive horses. Horses 1–5 yr old are the most susceptible to infection. Orthomyxovirus A/equine-2 was first recognized in 1963... read more , equine herpesviruses 1 and 4 Equine Herpesvirus Infection Equine herpesvirus 1 (EHV-1) and equine herpesvirus 4 (EHV-4) comprise two antigenically distinct groups of viruses previously referred to as subtypes 1 and 2 of EHV-1. Both viruses are ubiquitous... read more Equine Herpesvirus Infection , botulism Botulism in Animals read more , Potomac horse fever Potomac Horse Fever Potomac horse fever (PHF) is an acute enterocolitis syndrome producing mild colic, fever, and diarrhea in horses of all ages, as well as abortion in pregnant mares. The causative agent is Neorickettsia... read more (equine monocytic ehrlichiosis), equine viral arteritis Equine Viral Arteritis Equine viral arteritis (EVA) is caused by an RNA togavirus and produces clinical signs of respiratory disease, vasculitis, and abortion. Horses with EVA infection present with fever, anorexia... read more , rotavirus, West Nile virus, Hendra virus Hendra Virus Infection in Horses Hendra virus (HeV) is the prototype species of a new genus Henipavirus within the subfamily Paramyxovirinae and was first identified in Australia in 1994. The viral agent is endemic in... read more (Australia only), and Streptococcus equi (strangles). Vaccination programs are formulated based on the animal’s age, use, and level of exposure.

Broodmare vaccination is important to provide active immunity for the mare and passive immunity for the foal via transfer of colostral antibodies. Vaccination guidelines for foals have been modified because of the interference of maternal antibodies with the initial vaccination response. Sources such as the American Association of Equine Practitioners can provide the most current equine vaccination recommendations for horses in the US.

The following vaccination recommendations assume that foals are born to vaccinated mares and have absorbed adequate colostral antibodies with IgG levels >800 mg/dL.

Foals with failure of passive antibody transfer (ie, IgG levels < 200 mg/dL) and/or foals born to unvaccinated mares can receive their initial vaccination for equine herpesvirus 1 and 4, tetanus, and Eastern and Western equine encephalomyelitis beginning when they are 3–4 months old, followed by a second dose 4–6 weeks later and a third dose at 10–12 months. These foals can receive their first dose of rabies vaccine at 3–4 months, followed by a booster at 12 months. Influenza vaccination can be started at 6 months old. Foals born to mares that have never been exposed to or vaccinated against West Nile virus can receive their first vaccination at 3–5 months old.

Tetanus Vaccinations for Horses

The pathogen that causes tetanus Tetanus in Animals read more , Clostridium tetani, is present in all parts of the world. Tetanus occurs most commonly when wounds become contaminated with the organism from the soil. Vaccination is recommended for all horses and ponies annually. A horse with an unknown vaccination status that sustains an injury should receive a dose of tetanus antitoxin along with a dose of tetanus toxoid. A second dose of toxoid should be administered 4 weeks later.

Foals from vaccinated mares should be administered a three-dose series at 6, 7, and 9 months old. Foals from unvaccinated mares should receive tetanus toxoid at 3, 4, and 6 months. Whenever a vaccinated horse experiences a serious wound, a tetanus booster may be indicated.

Equine Herpesvirus 1 and 4 (Rhinopneumonitis) Vaccinations

Two types of equine herpesviruses Equine Herpesvirus Infection Equine herpesvirus 1 (EHV-1) and equine herpesvirus 4 (EHV-4) comprise two antigenically distinct groups of viruses previously referred to as subtypes 1 and 2 of EHV-1. Both viruses are ubiquitous... read more Equine Herpesvirus Infection vaccine are available, EHV-1 and EHV-4. The EHV-1 virus is the primary cause of abortion and also neurologic disease in horses. The EHV-4 virus is the primary cause of respiratory infections, especially in young horses. The control of rhinopneumonitis is by a combination of vaccination and good management practices.

To prevent abortion, a killed EHV-1 vaccine should be administered to pregnant mares at 3, 5, 7, and 9 months of gestation. Respiratory disease is best prevented using a combination vaccine of EHV-1 and EHV-4. There is no evidence that vaccination protects against the neurologic form of the disease.

Vaccine recommendations for foals are three doses every 4 weeks starting at 6 months, and a booster at 1 year. Pleasure and performance horses should be vaccinated every 3–6 months, depending on the risk of exposure. Broodmares should have an EHV-4 vaccination 2–4 weeks before foaling to ensure the availability of colostral immunity.

Encephalitis Vaccinations for Horses

Eastern equine encephalitis Meningitis, Encephalitis, and Encephalomyelitis in Animals Meningitis, encephalitis, and encephalomyelitis are terms used to describe inflammatory conditions of the meninges, brain, or brain and spinal cord, respectively. These inflammatory processes... read more Meningitis, Encephalitis, and Encephalomyelitis in Animals (EEE) virus has a wide distribution. This includes the eastern US, Central and South America, and eastern Canada. In the US, EEE occurs primarily in the southeastern states but has been reported in all states east of the Mississippi River. EEE in horses is nearly always fatal regardless of treatment. Infected horses usually become comatose, seizure, and die in 36–48 hours.

The Western equine encephalitis (WEE) virus is primarily located in the western US. In recent years, reports of WEE have not been common, probably as a result of adequate vaccination programs. The virus is not as pathogenic as EEE, and animals infected with WEE have a greater chance of survival. Mortality is usually 50%.

Venezuelan equine encephalitis (VEE) virus causes outbreaks of disease in horses in Mexico, Central and South America, and occasionally the southern US. The VEE vaccine is a single vaccine or in combination with EEE and WEE. Its need is limited to those horses traveling to or located in endemic areas.

West Nile virus (WNV) disease is considered a zoonotic disease similar to the encephalitis viruses. The bird population allows for maintenance of the virus, which is then transmitted by mosquitoes to both people and horses. There is very little risk of contracting the disease from any infected horses. Vaccination protocols for broodmares, foals, and adult horses are the same as those for Eastern and Western encephalitis. Combination vaccines that include EEE, WEE, and WNV are available.

Influenza Vaccinations for Horses

Influenza Equine Influenza Equine influenza is highly contagious and spreads rapidly among naive horses. Horses 1–5 yr old are the most susceptible to infection. Orthomyxovirus A/equine-2 was first recognized in 1963... read more is one of the most frequent causes of viral respiratory disease in horses and is highly infectious among susceptible horses. Therefore, vaccination is recommended for all foals, broodmares, and horses at risk of exposure, usually as a result of showing, racing, or shipping. Young foals from vaccinated mares, because of maternal antibodies, should be vaccinated at 9, 10, and 12 months. Foals from unvaccinated mares should be vaccinated earlier. The intranasal vaccine can be administered every 6 months in young, susceptible performance horses 2–4 years old. Vaccination is recommended every 6 months for horses exposed to other horses at equine events.

Rabies Vaccinations for Horses

Clinical signs of rabies Rabies Rabies is an acute, progressive encephalomyelitis caused by lyssaviruses. It occurs worldwide in mammals, with dogs, bats, and wild carnivores the principle reservoirs. Typical signs include... read more include the inability to eat or drink, disorientation, and incoordination. Rabies is fatal and also poses a health risk to those who handle infected horses. Prevention in horses is primarily via vaccination. Broodmares should be vaccinated 4–6 weeks before foaling. Foals from vaccinated mares should be vaccinated at 6 and 7 months old and again at 12 months. Foals from unvaccinated mares should be vaccinated at 3, 4, and 12 months. All adult horses should be vaccinated annually.

Potomac Horse Fever Vaccinations

Potomac horse fever Potomac Horse Fever Potomac horse fever (PHF) is an acute enterocolitis syndrome producing mild colic, fever, and diarrhea in horses of all ages, as well as abortion in pregnant mares. The causative agent is Neorickettsia... read more (equine monocytic ehrlichiosis, equine ehrlichial colitis) is due to Neorickettsia risticii. Vaccination is recommended in endemic areas in the US, such as near freshwater streams, rivers, ponds, and heavily irrigated pastures. Annual boosters in the spring are recommended. Pregnant mares should receive a booster before foaling. Although the vaccine may lessen the impact of the disease, it appears not to prevent abortion in pregnant mares.

Botulism Vaccinations for Horses

Equine botulism Botulism in Animals read more is mostly seen in the Mid-Atlantic area of the United States, but the disease has also been reported worldwide. The spores of Clostridium botulinum are found in the soil and are resistant to light, drying, and heat. In the US, the most common types are B and C botulism, although type A has been reported in the western US.

The type B vaccine gives good protection in adult horses. Adult horses and broodmares in areas where botulism is a potential hazard should receive three doses at 30-day intervals initially and then annual boosters. Foals from vaccinated mares in endemic areas should be vaccinated at 2, 3, and 4 months old, because colostral immunity does not always occur. Foals from unvaccinated mares should be vaccinated at 2, 4, and 8 weeks. The use of type B vaccine in areas where type C occurs has uncertain results.

Streptococcus equi Vaccinations

S equi infection (equine strangles, equine distemper) is highly infectious. Use of the IM or intranasal vaccine is recommended only in those situations or on premises where the disease has been a problem or for horses at risk (sharing water or nose-to-nose contact at shows/sales, etc). The IM vaccine involves three injections administered 2–4 weeks apart, starting at 4 months old in foals, with a booster at 12 months. If the intranasal vaccine is used, vaccination can begin at 6–9 months, with a second dose administered 3–4 weeks later and a third dose at 12 months.

Adult horses, if in potential disease situations, should receive an annual vaccination. Broodmares on endemic farms should receive an annual booster using the IM vaccine 4–6 weeks before foaling. Because of the increased risk of inducing immune-mediated purpura hemorrhagica, horses with titers to the SeM surface protein of S equi in excess of 1:1,600 may not need to be vaccinated.

Rotavirus Vaccinations for Horses

Foal diarrhea as a result of rotavirus infection can be a severe problem on some breeding farms. Single cases or a farm outbreak can occur. Therefore, pregnant mares should be vaccinated IM at 8, 9, and 10 months of gestation. This will increase the amount of colostral immunoglobulins. This vaccine is for use in particular situations or areas of high endemicity.

Equine Infectious Anemia Control

In the acute state, equine infectious anemia Equine Infectious Anemia (swamp fever) causes severe RBC destruction and anemia, and no vaccine is available. Once infected, a horse can become a carrier for life and is a threat to other horses. The virus is transmitted by bloodsucking insects. Currently, the disease is uncommon, and most horse owners are aware of its dire consequences.

A simple blood test, the Coggins test, is available to detect infected horses. A horse that tests positive cannot cross state lines and is required to be maintained in strict isolation for life. For horses participating in equine activities or being transported across state lines, proof of a negative Coggins test is required. Annual testing of every horse is recommended.

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