PARASITES IN HORSES
Equine Strangles seen in Southern Ontario
There have been numerous reports of cases of equine Strangles recently in Southern Ontario. Given the amount of misinformation and sense of fear in the horse industry surrounding this disease, we wanted to provide horse owners with accurate information on how to protect their horses.
Caused by the highly contagious bacteria Streptococcus equi.
Causes fever, yellow-green nasal discharge, and in many cases, abscesses within lymph nodes around the jaw and throat.
The majority of adult, otherwise healthy horses will fully recover from the disease without any medication or treatment.
Although vaccinating against Strangles does not completely prevent the disease, it does decrease the chance of the disease occurring and the severity.
The best method of preventing Strangles from entering a farm is to strictly quarantine all new incoming horses for 3 weeks, and immediately quarantine any horses showing yellow-green nasal discharge and fevers.
Strangles has been present in the horse population for decades, and periodically causes outbreaks on farms. Although most horses fully recover from the disease without treatment, it is highly contagious, can quickly spread between dozens of horses at one competition or show, and can cause their home farms to be put under strict quarantine for weeks or months. The disease has been maintained in the horse population by a small percentage of silent carriers who shed the bacteria in their nasal secretions.
Course of the Disease
The Strep. equi bacteria enters a susceptible horse’s mouth or nose and initially causes a fever. Within 2-3 days of the onset of a fever, the horse begins to shed the bacteria in its nasal secretion and can potentially spread the disease to other horses before nasal discharge is seen! Next, the horse will show yellow-green nasal discharge and swollen lymph nodes under the jaw and at the angle of the jaw. Many horses will develop abscesses of these lymph nodes that will eventually rupture and drain pus. Infection can also spread to the guttural pouches (the pair of air chambers on either side of the jaws). Although the disease is named Strangles, it is rare that a horse develops severe respiratory distress from these abscesses. Generally within 2-3 weeks the horse will resolve the infection, but some horses may continue to shed bacteria for 6 weeks or longer. <br>
A small percentage of horses will have the infection spread to the lymph nodes all throughout the body and cause a more serious form of the disease, termed Bastard Strangles. It has been frequently noted that Bastard Strangles is more likely to result when a horse with Strangles is treated with antibiotics early on in the disease, although this has not been definitively proven
Approximately 10% of horses recovered from an episode of Strangles will remain carriers of the bacteria in their guttural pouches, and can intermittently shed the bacteria and infect other horses for months or even years. This is thought to be how Strangles has persisted in the equine population for decades.
Confirming the Disease
The ‘gold standard’ test is to culture the bacteria from a nasal swab or by swabbing pus discharging from an abscess. This test takes 2-3 days for results. Silent carriers can be confirmed by passing an endoscope up the nasal passages and flushing the guttural pouches and using PCR to detect the bacteria.
Treatment depends on the horse and severity of the disease. It is best for your veterinarian to examine your horse and give specific recommendations. In general, it is recommended not to use antibiotics as it may cause the bacteria to spread further throughout the body and only slow down the course of the disease. Supportive care such as rest, a warm stall, moist, palatable food, and anti-inflammatories are used. Silent carriers can be treated to fully eliminate the infection. This involves instilling antibiotic gel into their guttural pouches using endoscopy.
The prognosis for the vast majority of horses is very good. Approximately 75% of recovered horses will develop a long lasting immunity against Strangles for 5 years or longer.
Once Strangles has been identified on a farm, strict quarantine measures should be put in place to prevent spread to remaining horses on the farm and other farms. Sick horses should be separated from apparently normal horses, and all horses should have their temperatures monitored twice daily. As soon as one develops a fever, this horse should immediately be placed on quarantine as it will soon begin shedding and infecting other horses. Humans should be very careful to not spread the bacteria on their hands, boots, tack and clothing.
An important step to prevent the arrival of Strangles and other diseases on your farm is to quarantine all newly arrived horses year round for a period of 2-3 weeks. This step is often missed on farms. Quarantine should include a stall, ideally in a separate barn, or at the very least, where there will be no nose-to-nose horse contact and no contact with boarders. Turn out and riding spaces should also have no nose-to-nose contact. Horses on quarantine should be tended to last by barn workers to prevent humans spreading disease to other horses, and tack and equipment should not be shared. When travelling off property with your horse, ensuring your horse, again, does not have nose-to-nose contact with new horses will also limit the spread of diseases.
Any horses that exhibits a fever and nasal discharge should ideally be placed on quarantine on the farm until Strangles (or other contagious diseases) have been ruled out. Remember, abscesses may not develop until later in the course of the disease, after the horse has infected others, or may never develop at all. So a `run of the mill snotty nose` may, in fact, be an early case of Strangles.
There is an intranasal vaccine available against Strangles. Although it does not completely prevent the disease, it greatly reduces the chance of developing the disease and the severity. Initially the vaccine is administered twice, 2-3 weeks apart, and then repeated yearly. It is important to note the vaccine should not be used in the midst of an outbreak on a farm and should only be administered to healthy horses.
A small percentage of horses who have recovered from Strangles produce a very high antibody response against the bacteria. If these horses are later vaccinated, they have a chance of developing a serious condition called Purpura Hemorrhagica, an excessive immune response resulting in painful, swellings of the limbs (stove pipe legs) and belly. This can be life-threatening and lead to permanent damage. These horses at risk can be identified with a simple blood test that measures their antibody levels against Strangles (titre). If your horse has a high antibody level, it is not recommended to vaccinate, and in fact, the horse does not need a vaccine as they are protected against Strangles.
Please feel free to contact Paris Veterinary Clinic with any questions or to discuss
your individual horse(s) situation. We are happy to help!