Equine Vaccination and Deworming

Hello everyone!

Spring time is here! So I thought it would be a good time to review the diseases that we vaccinate against every year and touch on deworming. So, here we go…

Eastern (EEE) and Western (WEE) Equine Encephalitis  This disease affects the nervous system of horses by causing inflammation (swelling) of the brain (encephalitis). It is spread by mosquitos from equid to equid. EEE and WEE are named after the area they affect, Eastern Encephalitis is found in eastern North America and has a 100% mortality rate (death rate) while Western Encephalitis is found in western North America and has a 75% survival rate but affected animals will have permanent damage. Symptoms and signs are related to nerve function impairment and can be seen as twitching, fever, abnormal behaviour, decreased vision, circling, difficulty swallowing or walking and seizures along with many other more non-specific symptoms. Vaccination begins as a foal with a booster one month later and then yearly boosters after that.


Tetanus This disease is caused by a clostridial bacteria that lives in the soil and??enters horses through wounds, especially if wounds are caused by sticks or metal. Tetanus also affects the nerve system and affects the horses stance, causes seizures, affects ability to eat, tail carriage and eventually the ability to breath causing death. A very characteristic feature of tetanus is the stance shown below and protrusion of the 3rd eyelid (eye appears to be sunken in with the inner corner rising up). You can treat tetanus with supportive care but success depends on the severity of the infection and prognosis is usually poor with permanent neurological damage as a result. Vaccination begins as a foal with a booster one month later and then yearly boosters and boosters with any traumatic lesion or puncture wound. tetanus tetanus2tetanus3

Rhinopneumonitis (equine herpes virus)  This disease is caused by a virus (2 different strains)and causes a number of life threatening symptoms. EHV-4 is the more common virus and is highly contagious and spread from horse to horse from secretions and fomites (objects that are infected from secretions). The clinical signs of EHV-4 are fever, cough and respiratory changes and less commonly neurological symptoms such as difficulty walking, hind end paralysis, loss of tail or bladder function, eating and behaviour changes and abortion in pregnant mares. Abortion most often occurs in the 7-11th month of gestation and is anywhere from 2 to 12 weeks post infection. EHV-1 is a less common virus but is more fatal as it is typically a neurological infection while EHV-4 is typically a respiratory infection. If infected horses do survive, they often shed the virus during stressful events and can be the source of outbreaks to naive horses. Vaccination can begin at any time but does require a booster one month later to be effective. After that the horse can be vaccinated annually, or bi-annually if they travel often and have contact with a wide variety of strange horses. Pregnant mares are recommended to have a vaccination every 3 months during pregnancy and 1 month before foaling to prevent abortion with a special version of the vaccine.


Equine Influenza The flu in horses typically affects horses 5 years and younger and causes respiratory symptoms. Symptoms include cough, fever, depression, nasal discharge and weight loss. Influenza, if untreated, can also progress to pneumonia and death. Equine Influenza is extremely contagious from horse to horse and can last for several weeks up to 6 months before full recovery is evident. If horses are brought back into work before recovery is complete, owners risk prolonging recovery and declining horse performance. Due to the high mutation rate of the influenza virus it is possible for a vaccinated horse to contract the illness. But studies show that vaccinated horses have significantly less symptoms and recover in a fraction of the time it takes an unvaccinated horse to recover and this is due to cross protection provided by the vaccine. Rest is vital for recovery as stressing the lungs through exercise doesn’t allow the damaged cells to repair and prolongs the duration of the illness. Vaccination can begin at any time but does require a booster one month later to be effective, after that the horse can be vaccinated annually, or bi-annually if they travel often and have contact with a wide variety of strange horses.

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West Nile Virus West Nile virus is another virus that attacks the neurological system. It is spread by a specific breed of mosquitos that appear in mid to late summer and the main host and source of disease are birds. The mosquitos feed from the birds and then can infect a number of other species including horses. West Nile can also infect humans as well thus it is tracked by the government. The first sign that the disease is present in your area is dead birds. It affects the brain just like EEE and WEE causing encephalitis which leads to a variety of odd neurological symptoms. Horses that contract WNV can be treated with supportive care only and usually have permanent neurological damage if they survive. Vaccination begins as a foal with a booster one month later and then annual boosters after that.

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Strangles  Strangles is an infection caused by a bacteria, Streptococcus equi equi, which causes the lymph nodes of the horse to enlarge and abscess. It also affects the horses respiratory system. Strangles is typically a young horse (ages 5 and under) disease that is extremely contagious and can have life threatening consequences but for the most part is not a life threatening infection. Clinical signs include fever, purulent discharge from the nose, depression, difficulty swallowing and breathing and large swellings in the throat latch area. When the lymph nodes swell very large it can make swallowing and breathing difficult for the horse and if not  treated the infection can stay in the guttural pouches and be a source of infection for horses in the future. Treatment is usually successful but different from normal bacterial infections because antibiotics are not given unless the case is very severe as it can block the natural immunity from developing and the horse may get Strangles again. Due to the extreme contagious nature of strangles, infected horses must be quarantined until 1 month??after recovery to prevent spread of the disease. This is because the bacteria can live in the environment for as long as 4 weeks. Fly control is also extremely important as they can spread the disease as well. Vaccination is recommended for horses as foals with a booster 1 month later then yearly until they reach around 5 years of age.


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Equine Infectious Anemia (EIA) This is a disease spread by mosquitos and caused by a virus that in the highly active form causes severe illness and death. It is endemic in Western Canada and Alberta in particular. It will always be around because it persists in the wild horse population. Clinical symptoms can range from a perfectly normal looking horse which is described as a carrier to a horse that is not visibly ill but is difficult to keep weight on and is a poor doer toa horse that has severe anemia, ventral edema, bloodshot eyes, depression, inappetence and generally weak. While there is no preventative vaccine or successful treatment there is a test that can identify positive horses called a Coggin test.  This is a simple blood test and is government regulated as this disease is a reportable disease meaning that the government is involved in its control mainly for importation, exportation and trade purposes. Many stables, shows and events are now requiring your horse to be tested and Coggins negative to participate to help prevent spread of this devastating disease.


Equine Deworming

There are 4 main worms that infect horses: Tapeworms, Strongyles, Pinworms, and Ascarids (roundworms).

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It is recommended to start deworming as a 4 month foal and every 2 months for 3-4 treatments. Babies in general have a large worm burden due to their natural instinct to eat feces and populate their gut flora. Always ask your veterinarian which dewormer to use on foals as large worm burdens if killed too rapidly can cause impaction of the intestines and death.

For older horses bi-annual deworming is typical if there are worms in the feces. Once in the spring to catch any encysted worms emerging from winter hibernation, and once in the fall after the first heavy frost to kill any worms obtained through the summer of grazing. It used to be recommended to deworm every 2-4 months but recent research has shown this method of deworming encourages resistance in the worms. By only deworming twice yearly any resistant genes in the worms are diluted out with non-resistant genes preventing a fully resistant worm population. If you are unsure whether your horse has worms or which types, a simple fecal float can ensure you are using the correct dewormer at the correct frequency.worms2worms

The most common deworming drugs are Moxidectin, Ivermectin, Fenbendazole, Praziquantal and Pyrantel. These are more commonly known by their brand names respectively: Quest, Eqvalan or Ivomec, Panacur or Safeguard, Quest plus or Eqvalan gold, and Strongid.

Fecal floats are always recommended when you are unsure if your horse has worms as regular worming may not be necessary. Fresh feces is processed in the laboratory and analysed and will give you the type of worm along with how many there are. After that your??veterinarian can recommend individual deworming protocols for each horse. Just make sure if you are collecting  your own fecal samples to submit that you clearly label which sample came from which horse so the results can be properly coordinated.

Always if you have any questions or concerns, contact your local veterinarian.

Happy Trails!

Dr. Stacey