By Dr. Monika Calitri, DVM
Most horse owners know that their horses should see the vet in the spring to get vaccinated, but what are they for and why are they important?
A vaccine is a biological preparation that improves immunity to a particular disease. They are important because they help protect your horse from becoming sick. AAEP, American Association of Equine Practitioners, provides guidelines to help formulate a vaccination program for each individual horse based on its potential exposure to various infectious diseases.
“Core” vaccines are considered to be safe, efficacious and protective against diseases endemic to a region. Core vaccines include Eastern and Western Equine Encephalitis, West Nile, Tetanus and Rabies. “Risk-based” vaccines are recommended for horses with increased exposure to certain infectious diseases. Some “risk-based” vaccines commonly administered in New England include Influenza, Equine Herpesvirus, Strangles, and Botulism.
Eastern Equine Encephalitis (EEE), also known as sleeping sickness, is transmitted by mosquitoes. It causes inflammation in the brain and spinal cord, resulting in a variety of clinical signs, some of which include fever, depression, blindness and recumbency. EEE is almost always fatal. Western Equine Encephalitis (WEE) is also transmitted by mosquitoes, however it is primarily found in the western states. WEE results in similar clinical signs as EEE, but is less fatal with approximately 50% of infected horses recovering. Another virus transmitted by mosquitoes is West Nile Virus. Not all horses infected with West Nile Virus will exhibit clinical signs. Some clinical signs exhibited by affected horses include fever, depression, ataxia (“wobbly gait”) and muscle fasciculations (twitching).
Tetanus is a disease caused by a neurotoxin originating from Clostridium tetani (an anaerobic bacterium). The spores of Clostridium tetani can live in the environment for years and infect puncture wounds, lacerations, and surgical sites. Common clinical signs resulting from infection include muscle contraction/spasm primarily of the head and face and protrusion of the third eyelid.
Rabies is contracted through the bite of an infected animal. It is always fatal and poses a risk for humans. Horses infected with rabies can exhibit a wide range of clinical signs, ranging from depression to colic. A few more commonly seen signs include hyperesthesia (irritability when touched), inability to swallow, and salivation.
Vaccinations against EEE/WEE, West Nile, Tetanus, and Rabies are highly effective and recommended for all horses residing in New England.
Recommendations for “risk-based” vaccines are based on a horse’s potential exposure to the following diseases.
Influenza is a highly contagious respiratory virus spread through aerosolized droplets when a horse coughs. Typical clinical signs include fever, serous nasal discharge, enlarged submandibular lymph nodes, and cough. Equine Herpesvirus (EHV Type 1 and EHV Type 4), also known as Rhinopneumonitis, causes respiratory disease that is spread through direct and indirect contact with nasal secretions. EHV-1 is also associated with neurologic disease. The vaccine provides protection against the respiratory form of the disease but not the neurologic form of the disease. Strangles is caused by the bacterium, Streptococcus equi subspecies equi. It is transmitted by direct or indirect contact with infected horses or sub-clinical carriers (ie. carriers of the organism that are not outwardly showing clinical signs). The ability for the organism to survive in the environment, in addition to subclinical carriers, makes Strangles a difficult disease to control during an outbreak.
The vaccines for Influenza, Equine Herpesvirus, and Strangles provide a degree of protection against the disease and can help lessen the course of disease, however, do not completely prevent disease. Therefore, it is important to decrease potential exposure when possible.
Botulism is the result of toxins produced by the bacterium, Clostridium botulinum. Horses ingest the toxin from eating decaying plant material or animal carcass remnants in feed, most commonly round bales of hay. Clinical signs include inability to swallow and muscle weakness progressing to paralysis.
It is important to understand the various potential infectious diseases and the protective vaccines available to the horse population to allow you to formulate an appropriate vaccination protocol for your individual horse under the guidance of your veterinarian.