Vaccinations for horses and disease prevention

Horses can be vaccinated for many different diseases. However, most horses do not need every single vaccination available, while others are more at risk for certain diseases. Read on if you have asked:

• When should I vaccinate my horse?
• What equine diseases can be prevented by vaccination?
• Can my horse have a bad reaction to a vaccine?
• Are there diseases that my horse cannot be vaccinated against?

There are currently fourteen different diseases that can be prevented in horses with the use of vaccines. Many of these diseases are deadly or can severely impact your horse’s quality of life. Some vaccinations are recommended based on risk of exposure and not given to every horse, or given to horses at different times or according to specific circumstances, while others are considered “core vaccines” for all horses.

All healthy horses should be vaccinated with the core horse vaccines as well as risk-based vaccinations that depend on their geographic location and lifestyle. The age at which specific vaccines are given and the frequency, or schedule, of each vaccination protocol are different. Vaccination schedules may change if:

• Your horse is sick or elderly
• Your horse is pregnant or a mare of active breeding age
• The horse is a young foal
• You compete with your horse and travel frequently together
• Disease risks are higher or lower depending on where you live

“It’s important to discuss vaccination schedules with an equine veterinarian who is familiar with the particular risks in your area and your individual horse,” states Vetster veterinarian Dr. Jo Myers.

There is a standard protocol for core horse vaccinations, including tetanus, rabies, West Nile virus, and viral forms of encephalitis. In addition, there are risk-based vaccinations you can discuss with your veterinarian based on your horse’s age, pregnancy/breeding status, lifestyle, and where you live. Vaccination guidelines vary from horse to horse and place to place.

Core vaccinations should be given to every horse who is healthy and old enough to receive them. Diseases all horses should be vaccinated for include:

• Tetanus a potentially fatal bacterial disease acquired through a puncture wound
• Rabies a fatal neurologic disease transmitted through animal bites which can also spread and is fatal to humans
• West Nile virus - a potentially fatal viral disease spread by mosquitoes
• Viral forms of encephalitis fatal viral neurologic diseases spread by mosquitoes

Each of these diseases is found all over the world and are often (or always) fatal in horses. They are preventable with routine vaccinations given by a veterinarian.

Tetanus in horses

Tetanus is a bacterial infection found in dust, soil, and manure. When a horse receives a puncture wound from an object where the bacteria is present, it can contract tetanus. Symptoms of tetanus include muscle stiffness, difficulty moving, and seizures, and is often fatal. The vaccination is given beginning at four to six months old. Horses should receive two doses four to six weeks apart if they have never been vaccinated before, and receive boosters annually after. Foals should receive a third dose to ensure proper immunity.

Rabies in horses

Rabies is a viral neurological disease and is rare in horses, but always fatal. It is spread by bites from other infected animals. Horses should receive one initial dose of the rabies vaccine beginning at four to six months of age and receive boosters annually. The rabies vaccination has not been thoroughly tested on pregnant mares but is often given during pregnancy regardless due to the high fatality rate of the disease.

Equine West Nile virus

The West Nile virus is spread by infected mosquitoes and causes uncoordinated movement, stumbling, muscle twitching, and collapse. The severity of infection ranges from flu-like symptoms to inflammation of the brain, called West Nile encephalitis. If the disease progresses to encephalitis, it is almost always fatal.

Horses should be vaccinated with two initial doses four to six weeks apart beginning at four to six months of age. Foals should be given a third initial dose to ensure immunity. Horses should receive boosters for West Nile virus every six to twelve months depending on the risk of mosquitoes in your area. More studies are needed to determine the risks of vaccination for pregnant mares, but the vaccine is often given based on the local risks.

Equine viral encephalitides

There are two main equine encephalitides: Eastern encephalomyelitis and Western encephalomyelitis. The type most prevalent depends on where you live, but both have similar symptoms. Sometimes called “sleeping sickness,” equine encephalomyelitis is a virus that attacks the brain and is spread by mosquitoes and other wildlife. Signs of infection include head pressing, difficulty swallowing, fever, uncoordinated movement, and paralysis.

Horses should receive two initial vaccination doses four to six weeks apart, starting at four to six months of age. Foals should receive a third dose at the age of ten to twelve months of age. All horses should receive boosters every six to twelve months depending on geographic risk.

Risk-based equine vaccines are recommended based on age, health, pregnancy status, and geographic location of the individual horse. Risk-based vaccinations for horses include:

• Rhinopneumonitis - a contagious virus spread by close contact with other horses
• Equine influenza - a highly contagious virus spread by close contact with other horses
• Strangles - a contagious bacterial infection spread by direct or indirect horse to horse contact
• Potomac horse fever - a potentially deadly bacterial infection spread by aquatic insects
• Botulism - a deadly neurotoxin transmitted by bacteria found in soil and forage
• Equine viral arteritis - a viral disease spread by respiratory or sexual contact between horses
• Anthrax a deadly bacterial infection spread in soil
• Rotavirus a viral disease that mostly affects young foals, spread by close contact with adults
• Snake bites - provides protection against most North American venomous snakes
• Leptospirosis - a bacterial infection spread by contamination of water and soil from wildlife urine

These diseases are often limited to specific geographic regions or spread when large numbers of horses come into contact with each other, such as during shows and competitions.

Rhinopneumonitis in horses

Rhinopneumonitis is a viral infectious disease spread by close contact with other horses. Also called equine herpesvirus (EHV). Rhinopneumonitis has three main types: EHV-1, EHV-3, and EHV-4. The vaccination covers types 1 and 4, which cause abortion in pregnant mares, respiratory infections, and neurologic disease. However, the vaccination does not protect against neurologic EHV; the most deadly form of the disease. EHV-3, which is not included in the vaccine, causes genital herpes and is not fatal.

Standard protocols call for horses who have not been vaccinated to receive three doses given four to six weeks apart, beginning at four to six months of age. Horses should receive an EHV booster every six to twelve months depending on how frequently the horse comes into contact with other horses. Pregnant mares should also be vaccinated during the fifth, seventh, and ninth months of gestation to protect against EHV abortion.

Equine influenza

Equine influenza is a highly contagious virus spread between horses, but is rarely fatal. The respiratory disease causes cough, nasal discharge, lethargy, and reduced appetite. The influenza vaccination is recommended for performance horses. Horses should be vaccinated based on the manufacturer’s recommendations, with a typical vaccination schedule being one or two doses 3-4 weeks apart, depending on the vaccine type, beginning at around six months of age.

Strangles in horses

Strangles is a highly contagious bacterial infection that causes upper respiratory infections in horses. Horses can catch strangles through direct contact with an infected horse or by contacting surfaces or equipment contaminated by infected horses. Due to the highly contagious nature of strangles, performance horses should be vaccinated. The vaccination schedule depends on the type of vaccine given, but typically involves a two or three-dose series given beginning at 6-9 months of age. Foals are  given an extra dose to ensure efficacy.

Potomac horse fever

Potomac horse fever is most prevalent in the Northeast and mid-Atlantic regions of the United States and Canada, though it can be found sporadically outside of these areas. The bacterial infection causes abortion in pregnant mares, diarrhea, colic, and high fevers, and spreads to horses by ingestion of aquatic insects.

The initial vaccination series against potomac horse fever  includes two doses given four to six weeks apart, beginning at three months of age. Potomac horse fever can be deadly, so horses should receive a booster every year at the start of summer and up to every three months for areas with high levels of the disease.

Botulism

Botulism is a deadly neurotoxin secreted by bacteria found in soil. The disease is endemic to Kentucky and the mid-Atlantic region of the United States. Botulism is rare in Canada. Horses typically contract botulism through feed and forage that has been exposed to the soil or wildlife carcasses. Round bales are more commonly affected. Sick horses will show signs of weakness, exercise intolerance, muscle tremors, uncoordinated movement, and reduced tongue strength, resulting in the inability to eat. Severe botulism is almost always fatal.

The botulism vaccination is initially given as a three-dose series with each dose given four weeks apart. Foals can be vaccinated as young as two weeks of age if they are at high risk, and pregnant mares should be vaccinated two to four weeks before foaling. Horses should receive a booster of the vaccine annually.

Equine viral arteritis

Equine viral arteritis (EVA) is a contagious viral disease in horses that causes abortion in pregnant mares, and can go undetected in herds until they breed. The vaccination is recommended for all breeding stallions, and mares that will be bred to stallions known to carry EVA. Horses should be vaccinated every year, at least three to four weeks before breeding. Vaccinated horses need to be isolated from the rest of the herd or unvaccinated horses for three weeks after vaccination as they can shed the virus in their respiratory secretions.

Anthrax in horses

Anthrax is a deadly bacterial infection spread through ingestion or inhalation of the bacteria, or a penetrating injury. Anthrax bacteria is found worldwide, but is most prevalent when there is a heavy rain after an extended period of drought, which brings the spores to the surface. Anthrax in horses is usually acute, causing symptoms including severe colic, difficulty breathing, fever and seizures. The disease is highly deadly, causing an infected horse to die within two to four days after exposure.

The anthrax vaccination is given once annually, with an optional second dose given two to three weeks later in highly affected areas. The vaccination is not recommended for pregnant mares and has not been studied in foals.

Equine rotavirus

Rotavirus damages the lining of the intestines, causing severe diarrhea and dangerous weight loss. Foals are most at risk of infection, and the disease is rarely seen in adult horses. The rotavirus vaccination is recommended for pregnant mares, given at eight, nine, and ten months of gestation. Unvaccinated foals catch rotavirus from exposure to the feces of unvaccinated adult horses or from an unvaccinated mother.

Snake bites

Although snake bites are a separate category of illness from viral infections, they are still life threatening and preventive inoculation is available. The snake bite vaccination helps reduce the effects of snake venom from most venomous snakes in North America. However, the vaccination does not protect against cottonmouths, Mojave rattlesnakes, or coral snakes. Horses in areas with large populations of venomous snakes should be vaccinated. The initial snake bite vaccine is a three-dose series given four to six weeks apart in horses older than four months of age. Horses can receive boosters every six months. It is unknown if the vaccine is safe for pregnant mares. Note: Snake bites are always a medical emergency, even if the animal receiving the bite has been inoculated. The vaccine helps buy time to get to emergency medical services, but it does not eliminate the risk of permanent injury or death.

Leptospirosis in horses

Leptospirosis is a bacterial infection spread when wildlife urine containing the bacteria contaminates soil, forage, and standing water. The disease causes loss of appetite, jaundice, fever, abortion, and blindness in horses. In addition, leptospirosis is zoonotic, meaning horse owners can catch the disease from their infected horses. The initial vaccination is a two round series given four to six weeks apart in horses older than six months of age. Leptospirosis is most commonly found in temperate, wooded areas with abundant wildlife and stagnant water.

Though it is rare, horses can have adverse reactions to vaccinations. It is important to note there is a difference between an adverse reaction and an immune response. Immune responses include:

• Low-grade fever
• Soreness at the injection site
• Muscle soreness
• Mild lethargy

Adverse reactions are more serious, and horse owners should contact their veterinarian right away if their horse shows symptoms soon after vaccination. Adverse vaccine reactions in horses include:

• Hives
• Abscess or infection at the injection site
• Anaphylaxis
• Colic
• Purpura hemorrhagica: swelling of the lower limbs, skin sloughing off, red spots on the mucous membranes

Severe adverse reactions are rare and the benefits of vaccines outweigh the risk of having a reaction. Horses receiving a vaccination for the first time should be closely observed for the first few hours, and vaccinations should only be given by veterinarians.

Though there are many diseases that can be prevented with vaccines, there are some that we do not currently have vaccinations against. Horses cannot currently be vaccinated against:

• Equine infectious anemia
• The neurological form of equine herpesvirus
• Tick-borne diseases
• Pigeon fever
• Most toxicoses
• Non-infectious diseases

It is important to know which diseases are prevalent in your area, can and cannot be vaccinated against, and other preventive measures to take along with vaccination. An equine vet in your area can help you decide what vaccines and management strategies are best for your horse.

Vaccinations are essential for the health and well-being of your horse. Always consult a veterinarian about vaccination scheduling and parasite risks for your geographic area. Finally, never vaccinate a horse without the guidance of your vet. Connecting with an online vet is the perfect way to discuss the prevention needs of your horse.

What vaccines do horses need every year?

The core vaccines that horses receive every year include tetanus, rabies, West Nile virus, and viral encephalitides. Your horse may need additional vaccinations on a regular basis depending on your lifestyle and where you live. Ask a veterinarian about what risk-based vaccines your horse may need.

How often should horses be vaccinated?

Different vaccines are given on different schedules depending on the specific circumstances of the individual horse. In addition, horses more at risk for some diseases may need to be vaccinated more often than others. There is no one-size-fits-all vaccination schedule for all horses.

How many years do you continue to vaccinate? Do I still need to vaccinate my senior horse?

As horses get older, their immune systems grow weaker. Senior horses should continue to be vaccinated on a regular basis and may need to be vaccinated more often than before. Always consult a veterinarian about your senior horse’s vaccine schedule.