The following information is provided as a client handout from the Bayer Agriculture Division. Copyright 1997 Bayer Corporation.

Strangles is an extremely contagious disease of the horse's upper respiratory tract. It is caused by Streptococcus equi, a type of bacteria that is spread from one horse to another by inhalation or ingestion of purulent exudates, either directly (horse-to-horse contact) or through environmental contamination.

The spread of strangles infection is rapid and often reaches 100% of the susceptible population. Young (6 month to 5 year old), nonvaccinated horses are most at risk for infection. Strangles occurs most frequently on farms where many horses are kept and where movement of horses into and out of the area is common.

Fortunately, serious illness due to strangles is rare and usually associated with the bacteria spreading beyond the upper respiratory tract. When such complications occur, lymph nodes throughout the body, or even organs such as the liver, spleen, kidneys, or brain, can be invaded by the bacteria. This syndrome is referred to as "bastard strangles." A rarer and more serious complication is purpura hemorrhagica, which is an immune reaction that damages the horse's blood vessels and may be fatal.

Clinical Signs

Infected horses become depressed, lose their appetite, develop a 104-106° F fever and a cough. A thick, yellow nasal discharge is present, and lymph nodes of the head and neck swell. Sometimes the lymph nodes swell enough to restrict breathing, which is how the disease got its name. After a week or two the abscessed lymph nodes of the head and throat may rupture and drain.

Diagnostics

The clinical signs of strangles, especially high fever and abscesses, are usually enough to make a diagnosis. Bacteria cultured from the abscess material can be identified for a definitive diagnosis.

Treatment

Horses suspected of having strangles should be isolated, kept warm and dry, and encouraged to eat soft, palatable feed (because swallowing is painful). The use of antibiotics in strangles is controversial. Complete drainage of the abscesses, along with regular flushes of the ruptured lymph nodes until healing occurs, are necessary to resolve the infection. The purulent material from the abscesses is infectious, and contaminated objects, including boots, hands, tack, hay, stall, and soil, should be cleaned and disinfected or discarded. "Bastard strangles" and purpura hemorrhagica are treated on an individual-case basis. Horses should be rested and only gradually brought back to work or training after a bout of strangles.

Prevention

Strict quarantine of any new animals on the premises should always be enforced for up to six weeks. Vaccination of all healthy horses should be done routinely on high-risk farms and in endemic herds, or in the face of an outbreak. It must be remembered that clinically recovered horses may shed the bacteria in nasal secretions up to several months after illness. Recovered horses should not be considered free of infection until bacterial cultures are negative. If an outbreak occurs, all exposed or contact animals should be monitored for temperature rises or other signs of illness.