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Vaccination Info


Equine Vaccinations

A little background on diseases we vaccinate against


Tetanus is a bacterial infection caused by the bacterium Clostridium tetani. This bacterium is found ubiquitously in soil. Almost all mammals can acquire tetanus; however, horses are the most sensitive of all our animals. The infection is often acquired through puncture wounds. Once infection begins, the bacteria create a neurotoxin, which is absorbed by the motor neurons and travels to the spinal cord. The end result is muscle spasms, severe stiffness, a sawhorse stance, and lockjaw. In unvaccinated horses, tetanus is usually fatal.

Eastern & Western Equine Encephalitis Virus

Eastern & Western Equine Encephalitis viruses (EEE & WEE) are spread via mosquito vectors to susceptible horses, and therefore infection is most prevalent from May to October. Once infected, the virus infects the lymphatic system. Initially, horses are quiet and depressed and signs progress to impaired vision, wandering, head pressing, circling, irregular gait, and convulsions. The horse can pass away 2-3 days after onset of clinical signs. We do see the Eastern form of this disease in Maryland and Pennsylvania. While there are no specific treatments to this disease, vaccination greatly reduces the severity of clinical signs.

Equine Influenza

Equine Influenza is a highly contagious respiratory disease caused by a virus. Equine flu virus is introduced by an infected horse and spreads, rapidly, from horse to horse in respiratory secretions. Clinical signs of infection vary in severity based on the immune status of the individual horse, with older and very young horses at highest risk. While some infected horses show only mild or unapparent clinical signs, others may develop a high fever, dry cough, profuse nasal discharge, depression, and anorexia. If severe, laminitis, difficulty breathing, and pneumonia may occur. Mildly affected horses will recover in 2 to 3 weeks. Vaccination will help limit the severity of infection. If your horse will be traveling to shows or will be exposed to new horses, we recommend having Equine Influenza vaccine on board.

West Nile Virus

West Nile Virus is a viral infection that is spread by mosquito vectors to susceptible horses, humans, and other mammals. The mosquitoes become infected after feeding on infected birds. When an infected mosquito feeds on a horse, the disease can be transmitted to the horse. Signs of clinical disease include trembling, stumbling, sleepiness, dullness, facial paralysis, and difficulty passing urine and manure. Some horses may develop mild fevers, blindness, and seizures. Signs of West Nile Virus appear 5 to 15 days after the horse is infected. Infection is most common from May to October. This disease can be fatal to horses. Vaccination helps limit severity of clinical signs associated with WNV by preventing viremia.


Rabies is a highly fatal viral disease that infects all mammals, including humans. Rabies is transmitted in saliva of an infected animal (usually wildlife). Therefore, when a rabid animal bites our domestic animals, infection can occur. In general, an unvaccinated animal that is bitten will show clinical signs 3 to 12 weeks after the bite has occurred. However, this period may vary from a few days up to 6 months. Clinical signs of rabies include inappetance, difficulty eating, abnormal behavior, loss of balance, paralysis, altered vocalization, and seizures. Progression to death is rapid. No treatment exists at the current time. Vaccination prevents development of the disease in nearly all vaccinated individuals. Since there is a risk of human exposure, we strongly recommend vaccination of all horses.

Potomac Horse Fever

Potomac Horse Fever (PHF) is an acute bacterial disease that can cause severe diarrhea in horses. First identified in Maryland, PHF is caused by Neorickettsia risticii bacteria, which is believed to be transmitted by an insect host. Since it is transmitted in blood, lice, ticks, or fleas are suspected as transmitters of the disease. Infection is highest in July, August, and September and is common in Pennsylvania and Maryland. In our practice, we have treated cases as late as mid-November. Clinical signs include fever, depression, off feed, reduced gut motility, colic, diarrhea, and laminitis. The disease lasts 5 to 10 days, if untreated, fatality rates for untreated horses can be up to 30 percent. While the vaccine may not prevent your horse from getting the disease, it will help reduce the severity of clinical signs of PHF.

Equine Rhinopneumonitis

Equine Rhinopneumonitis is a herpes virus infection caused by EHV 1 and EHV 4. The virus is spread through direct or indirect contact to infected nasal secretions, an aborted fetus, placentas, or placental fluid. Infection most often results in upper respiratory tract infections and clinical signs include fever, congestion and nasal discharge, eye discharge, swollen lymph nodes, and cough. Equine Herpesvirus 4 infection is limited to the respiratory tract; however, Equine Herpesvirus 1 may cause abortions in unvaccinated mares and may cause neurologic signs, such as hind limb incoordination, loss of bladder and tail function, and recumbency. Mature horses that are exposed to the virus can develop immunity to the respiratory form of the disease, but not to the abortigenic and neurologic form. Young horses (less than 5 years old), horses in contact with pregnant mares, and horses that attend shows and events should be vaccinated against this disease. If you plan on breeding your mare, she should receive this vaccine 3, 5, 7, and 9 months of gestation.


Strangles is a bacterial infection of the upper respiratory system in horses. It is transmitted though the nasal discharges of an infected individual and is highly contagious. An infected horse can transmit the disease for 4 weeks or more. In the upper respiratory tract, the bacteria infects local lymph nodes, where they causes lymph node enlargement and abscesses that can rupture. Once in the lymph system, the bacteria can spread to other lymph nodes in the body, such as in the abdomen, and cause abscesses there. This is known as "Bastard Strangles." In an unexposed population (such as a barn), nearly 100% of horses may develop the disease if exposed to an infected individual. Signs of upper respiratory infection include swollen lymph nodes, difficulty swallowing, fever, nasal discharge, and guttural pouch infection. Prevention includes quarantining any new addition to the herd for several weeks before turning out with the rest of the herd. Vaccination is another tool to help reduce severity of the disease. While it does not prevent disease, it limits the severity of disease. Horses traveling to shows or events may benefit from having this vaccine on board.


Botulism is a paralytic disease that is caused by ingestion of a toxin produced by Clostridium botulinum bacteria. Clostridium is ubiquitous in soil and in decomposing animal and plant material. In horses, botulism is often acquired by eating feed with the bacteria in it, or through wound infection. Hay in round bales or large square bales are common sources of botulism. In foals, ingestion of spores of C. botulinum can create "Shaker Foal Syndrome." Clinical signs of botulism in horses include diffuse muscle paresis and paralysis, difficulty chewing and swallowing, recumbency, and rapid death. Removing moldy or spoiled feeds will help prevent disease. In addition, vaccination against Botulism will help prevent infections. We recommend all horses feeding off round bales or large square bales be vaccinated.