Strangles is a highly common and contagious disease caused by the bacteria Streptococcus equi equi, which many horses are exposed to and infected with at a young age. The disease is highly infectious.

Transmission: Strep equi is spread from horse to horse through direct contact. Horses can also contract the disease by coming into contact with contaminated surfaces.

Incubation Period: The incubation period is the time from exposure to the virus to when a horse shows clinical signs of infection. The incubation for strangles organisms is three to 14 days.

Shedding Period: A recovered horse may be a potential source of infection for at least six weeks after the clinical signs of strangles have resolved. Horses who have been infected but are clinically healthy can continue to incubate and shed the bacteria.

Carrier status: Some horses that have recovered from the disease can become long-term, periodic shedders and can cause outbreaks when introduced to new herds.

Clinical signs: Clinical signs can range from non-clinical to clinical. Typically, a fever precedes other clinical signs by 24 to 48 hours. As the disease progresses, abscesses form in the mandibular lymph nodes (in the throatlatch and below the jaw), causing an often thick white and yellow mucus nasal discharge. This swelling is the inspiration for the disease’s common name. Due to the swelling, the horse could have difficulty swallowing and have a cough or make a wheezing sound. In rare cases, with complications, a horse can experience Purpura hemorrhagica, which is a bleeding from the capillaries that causes red spots on the mucous membranes and swelling of the limbs and head.

Diagnosis: Diagnosis is made through culture of nasal wash, nasal swab, or pus aspirated from abscesses or through PCR testing.

Treatment: Any treatment decisions should be made by a veterinarian, but most treatment is supportive care. Use of antibiotics in infected horses is restricted to those with severe clinical signs, such as respiratory difficulty, as most horses recover without antibiotic treatment. Horses treated with antibiotics early in the course of infection may avoid lymph node abscesses but may not develop immunity to the disease.

Prognosis: Strangles is rarely fatal and horses usually make a full recovery in three to four weeks with few complications. Horses who have been infected with Strangles can maintain long-term immunity to that bacterial strain.

Prevention: Intranasal and intramuscular Strangles vaccines are available. These are considered risk-based vaccines by the American Association of Equine Practitioners (AAEP) and may be used to prevent or lessen disease severity in at-risk horses. Consult a veterinarian to determine if vaccination is appropriate for your horse.

Any surfaces that are contaminated with mucus or other nasal discharge from infected horses pose a threat of infection to healthy horses. After an outbreak, cleaning should involve removal of all organic material from surfaces and subsequent disinfection of water containers, feeders, fences, stalls, tack, and trailers.