Equine Vaccines

Spring time is coming! Is your horse up to date on vaccines? Do you know how a vaccine works? Do you know what we vaccinate for and why? Read along to find out the answers to these questions.

A vaccine is made up of an antigen, a tiny particle of a certain bacteria or virus that has been either killed or modified. This alteration doesn’t cause disease, but causes an immune response, which produces antibodies that protect our animals from that particular bacteria or virus. We vaccinate our animals prior to exposure to these bacteria or viruses so that their immune system can mount a response that can reduce or fully eliminate the clinical signs that we see, thus we never perceive that animal to have any sickness. No vaccine is 100% effective, but it can greatly reduce the severity of disease, which can mean the difference between life and death.

In this region of Virginia we have certain “core vaccines” and risk-based vaccines that differ from other regions of the US. Core vaccines are determined by which diseases are endemic or very prevalent in our area. Our core vaccines include eastern equine encephalitis, western equine encephalitis, tetanus, rabies and west nile virus.

Eastern equine encephalitis (EEE) is a mosquito borne virus that has a mortality (death) rate of up to 90%. The disease causes swelling of the brain and spinal cord. Symptoms include impaired vision, aimless wandering, convulsions and death. Once an infected mosquito bites a horse, it can take three to ten days for symptoms to appear. This disease is reported in our area, which is why we recommend this vaccine as a core vaccine, especially prior to mosquito season.

Western equine encephalitis (WEE) is also a mosquito borne virus which in recent years has not caused disease in many animals, but continues to be detected in mosquitoes and birds.

Tetanus is usually a fatal disease caused by a potent neurotoxin from the anaerobic, spore-forming bacterium, Clostridium tetani. Spores of Cl. tetani survive in the soil/environment for many years. Tetanus is not a contagious disease but can contaminate wounds including puncture wounds, open lacerations, surgical incisions, exposed tissues such as the umbilicus of foals and reproductive tract of the mare after foaling (especially in the event of trauma or retained placenta). This vaccine is recommended anytime there is a fresh wound/ laceration especially if the vaccine was done over 6 months ago, prior to surgery and/or as part of routine vaccines.

Rabies is a neurologic disease of many different warm-blooded mammals, which has great public health significance and is 100% fatal. The virus migrates via nerves to the brain where it initiates a rapidly progressive, fatal encephalitis. Exposure occurs after a bite from an infected animal, most commonly from wildlife such as such as a bat, skunk, raccoon, or fox. If a bite from a bat occurs, it is almost always imperceptible to the human eye, so don’t assume it didn’t happen because you don’t see a bite. This vaccine is very important for all of our pets from dogs and cats to horses to pet goats and sheep.  Each year in our practice, we will see rabies positive horses and livestock.

West Nile virus is a mosquito borne disease that acquires the virus from reservoir birds. The signs of disease can be similar to EEE/WEE, such as muscle tremors, hypersensitivity of the skin, loss of coordination, even recumbency and the inability to stand. WNV has a mortality rate of 33% with almost 40% of the surviving horses still having residual signs of disease such as gait abnormalities or behavioral changes. Therefore, it is an integral part of our core vaccines and is boosted every 6 months.

Each patient will be evaluated to determine which vaccines should be administered at particular intervals.

Risk based vaccines include lyme, botulism, strangles, influenza, rhinopneumonitis, and Potomac horse fever. We will discuss the risk of each of these vaccines regarding your individual horse and situation.

Lyme disease is carried and transmitted by ticks that are attached to the body for at least 24 hours.  We have a high prevalence of Lyme disease in southwest Virginia.  A recent study determined that nearly 50% of our equine population in the northeast is infected or has been infected. Therefore, we are now recommending vaccination in addition to tick repellents. Clinical signs include low-grade fever, stiffness and lameness in more than one limb (shifting leg lameness), muscle tenderness, sensitivity to touch, swollen joints (rarely), and behavioral changes. Current studies suggest that the vaccine needs to be boosted every 6 months after initial vaccine series to be effective.

Botulism is a disease caused by toxins that are produced by Clostridium botulinum, which is present in the soil and more commonly contaminated hay. The hay becomes contaminated during the baling process where it can pick up small animals into the baled hay. Clinical signs include weakness progressing to paralysis, inability to swallow, and frequently, death. If you are currently feeding round bales, your horse could be at an increased risk. This vaccine is particularly important for breeding and or pregnant mares as it transfers immunity to the foals to prevent the diseased, “shaker foal syndrome.”

Strangles is a disease caused by streptococcus equi equi and causes clinical signs such as, fever (102-106 F), dysphagia (inability to eat) or anorexia, stridor (abnormal sound to breathing), lymphadenopathy (enlarged lymph nodes), and copious nasal discharge. This disease is highly contagious and will cause barns to be quarantined until all horses test negative for this disease, which can take several months.  This vaccine is recommended in endemic areas or to horses in high risk situations, such as competitive showing or trail riding with multiple horses. The organism is transmitted via direct contact with infected horses or sub-clinical shedders (horses that do not have outward signs of disease), or indirectly by contact with water troughs, hoses, feed bunks, pastures, stalls, trailers, tack, grooming equipment, nose wipe cloths or sponges, attendants’ hands and clothing, or insects contaminated with nasal discharge or pus draining from lymph nodes of infected horses. After natural infection horses, can become carriers for the disease and intermittently shed the organism.

Influenza and rhinopneumonitis are two viruses that are highly contagious and the viruses spread rapidly through groups of horses in aerosolized droplets dispersed by coughing. Equine influenza, caused by the H3N8 orthomyxovirus, is one of the most common infectious diseases of the respiratory tract of horses. Horses that are 1-5 years old and or have frequent interaction with large numbers of horses are most at risk. Equine herpesvirus type 1 (EHV-1) and equine herpesvirus type 4 (EHV-4) infect the respiratory tract, the clinical outcome of which can vary in severity from sub-clinical to severe respiratory disease. Clinical infection is characterized by fever, lethargy, anorexia, nasal discharge, cough, and mandibular lymphadenopathy. Most adult horses have built up enough immunity so that disease is not normally severe. This virus can also cause abortion and neurologic disease. Currently our vaccines only protect against the respiratory and reproductive forms of this disease. This vaccine can be administered as frequently as every 3 months to horses considered at high risk, but most often every 6 months.

Pneumabort vaccine prevents against abortion due to equine herpes virus EVH-1. This vaccine is administered at particular intervals towards the end of prenancy.

Lastly, Potomac horse fever is a disease caused by Neorickettsia risticii. Vectors are gnats, small biting insects and the disease is found most often in areas close to water. Clinical signs associated with this disease include, fever, (mild to severe) diarrhea, laminitis, mild colic, decreased abdominal sounds, and rarely abortion. The disease is seasonal, occurring between late spring and early fall in temperate areas, with most cases in July, August, and September with the onset of hot weather. This vaccine is boosted every 6 months.

With any vaccine there is a risk of adverse reactions. Adverse reactions are not always predictable and are inherent risks of vaccination. Adverse reactions can include pain or swelling at the injection site, sore neck, fever, lethargy or anorexia that is usually self-limiting. Signs of colic, hives, trouble breathing or anything else of concern should be brought to the veterinarians’ attention and treated immediately. If an adverse reaction should occur, we can take preventative measures at the next visit, such as splitting vaccines into multiple appointments or premedication to reduce the signs seen.

Please call us with any questions or concerns you may have in regard to a vaccine schedule for your particular horse.

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