Fact Sheet

Equine Strangles Strangles is an important disease because it can spread quickly through horse populations

Overview Not all horses exposed to the bacterium Strangles is a highly contagious and de- become infected. Infection depends on the bilitating equine disease caused by the bac- amount of the horse is exposed terium equi. Strangles is an to, the immune status of the horse, and important disease worldwide because it is underlying conditions such as stress, nutri- highly contagious (meaning it can spread tion, and pre-existing diseases. All ages of quickly through horse populations). horses are susceptible to S. equi; however, foals and young horses are most suscep- Clinical Signs tible because they often have lower (not as The most common clinical signs ob- protective) immune responses. This disease served in horses with S. equi are a mucopu- is more commonly seen in horses with ex- rulent nasal discharge (a greenish, yellow, posure to outside horses through travel to or white “snotty” discharge), fever, loss of competitions or those maintained in large appetite/anorexia, depression, cough, and herds with a mobile horse population. swellings that are a result of abscessation of the lymph nodes (usually the nodes lo- Diagnosis cated in the head and neck region) due to Diagnosis of horses with active signs of in g Dr. Na nc y S. Lov an accumulation of pus. Swollen lymph nodes, a common clinical sign strangles relies on the clinical presentation The lymph nodes can become so en- of strangles, usually burst and drain infectious of the horses and culture identification of S. larged that swallowing is painful and the thick, yellow pus. equi in swabs of nasal discharge and lymph or can be compressed, node contents. Diagnosis of chronic shed- causing labored breathing (hence the term, How S. equi Causes Disease ders of the bacteria is more challenging “strangles”). An affected horse might stand How long S. equi can survive in the and requires collection of nasopharyngeal with its head and neck stretched out to re- horse’s environment is unknown. If the wash samples with more extensive testing lieve the pressure caused by the swollen area is protected from ultraviolet light and through PCR and culture. lymph nodes. The enlarged lymph nodes the bacterium does not have competition usually burst and drain thick, yellow pus. from soil flora, it can survive for several Treatment The lymph nodes in the throat area can weeks. It is spread in the pus from infected Suspected strangles cases should be ex- burst into the guttural pouches and result horses’ noses, draining lymph nodes, or by amined immediately by a veterinarian to in copious nasal discharge. This pus is con- coughing. A horse shedding the bacterium confirm the diagnosis, alleviate some of the taminated and can spread the disease. can infect any object in the barn, including signs of disease, prevent the development In rare cases S. equi can infect lymph tack, feed and water buckets, shared water of secondary complications, and limit the nodes in areas other than the head and sources (such as automatic waterers and spread of S. equi to other horses. neck (such as the chest or abdomen). This tanks), brushes, and bedding. S. equi can Horses with strangles should be isolated is called “bastard” or metastatic strangles. also be transmitted by direct nose-to-nose for six to eight weeks. Follow strict hygiene Horses severely affected by strangles can contact between horses or even by flies. measures and disinfecting to ensure the die or require euthanasia. S. equi also can In classic strangles S. equi invades the bacterium is not carried to other horses on cause immune complexes that damage tonsil tissue then enters the regional lymph clothing, buckets, or vet equipment. Test blood vessels (called purpura hemorrhagi- nodes. Within three to eight days the horse to see if the horse is still shedding bacteria ca) and subsequently cause limb and head develops clinical signs. Once the abscesses prior to contact with other horses. swelling, circulatory failure, and death. rupture and drain, recovery is typically un- Many strangles cases do not require spe- Horses with partial immunity to S. equi eventful and occurs in approximately two cific treatment, and the use of antibiotics or that were infected with a less-virulent weeks. Horses can remain infective for is controversial. Thus, it is critical to in- strain of the bacterium can show an abbre- weeks after recovery, and a small number volve a veterinarian in developing a treat- viated course of disease with only minor or continue to shed the bacteria intermittently ment plan. Nursing care is advocated and no lymph node abscessation. This is called for a prolonged time—even years—despite involves warm compresses to relieve pain the catarrhal form of strangles. appearing completely healthy. caused by the swollen lymph nodes. If the

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Fast Facts enlarged lymph nodes are compressing the cause outbreaks of disease when mixed ■ Strangles is caused by the bacterium Strep- trachea or pharynx and making breathing with susceptible horses. tococcus equi subspecies equi and is an difficult, the veterinarian might lance the important, highly contagious respiratory lymph nodes or perform a tracheostomy to Prevention tract infection of horses. allow the horse to breathe easier. Draining To prevent introducing strangles to your ■ Classic signs of disease include a nasal dis- lymph nodes can be lavaged until they are facility, isolate all new horses two to three charge, swelling/abscessation of the lymph ready to seal and heal. weeks to ensure they do not develop signs nodes of the head and neck, fever, cough- of strangles prior to mixing with resident ing, difficulty eating, and lethargy. Prognosis horses. Take the new horses’ temperatures ■ Metastatic or “bastard” strangles Most horses recover from strangles with- twice a day for early detection of infectious occur when the bacterium infects areas in seven to 10 days from the onset of clini- disease. A veterinarian should examine all elsewhere in the horse’s body, such as the cal signs with no long-term residual health newly introduced horses prior to mixing. chest, abdomen, or brain. concerns. Non-fatal complications associ- Depending on the health history of the new ■ Recovery for most horses occurs unevent- ated with strangles include post-strangles arrival, you can test to detect S. equi. fully within six to eight weeks with appro- inflammation of the heart muscle (myo- Two strangles vaccines are available: a priate nursing care. carditis), cellulitis (inflammation of the subunit M-protein-based vaccine for in- ■ To minimize the spread of infection, all skin tissues), laryngeal hemiplegia or “roar- tramuscular use and a modified live bacte- infected horses should be immediately ing” (a noise caused when the airway isn’t rial vaccine for intranasal administration. quarantined and strict hygiene measures fully operational), anemia during recovery, There are pros and cons associated with should be instituted. and pus-filled guttural pouches. each vaccine that should be discussed with ■ Carriers or chronic shedders can occur Remember recovered horses can be in- your veterinarian. following recovery in a small percentage of fective and should be isolated from other Carriers can be identified by detecting horses with S. equi; these are an important horses for at least eight weeks after resolu- S. equi genetic material (DNA) using a source of infection for susceptible horses. tion of clinical signs and optimally tested polymerase chain reaction (PCR) test on ■ Vaccination against S. equi might be ben- to determine their shedding status. Horses nasopharyngeal lavage samples or samples eficial depending on risk factors for the with persistent infections of the guttural from the guttural pouches. Use of the live disease and your horse’s experience and pouches can serve as carriers of strangles S. equi vaccine in the previous 30 days can should be discussed with your veterinarian. and are major sources of infection that can interfere in this process. h