Strangles is highly contagious and found worldwide in horses of all ages. Younger horses between one to five years of age are most susceptible to infection.
Horses contract strangles by inhaling or ingesting the gram-positive bacteria Streptococcus equi. After the bacteria incubate for a week or less, they often cause symptoms such as fever and decreased appetite. Once infected, the bacteria travel to the respiratory tract and pharynx, causing significant inflammation and pain. Subsequently, the bacteria infect the lymph nodes surrounding the throat, or the submandibular, submaxillary, and retropharyngeal lymph nodes, causing them to swell and become abscessed. The disease generally lasts two weeks from the time that abscesses form and begin to drain.
In cases of "bastard strangles," abscesses form in other parts of the body, including the chest and abdomen. These abscesses may open up and drain, causing severe, life-threatening infection and inflammation. Such cases are very difficult to treat, and may lead to death. Other causes of death include central nervous system infections, heart disease, pneumonia, asphyxiation, and sepsis, which is an overwhelming infection of the blood stream.
