Once horses are exposed, they begin to show signs of the disease in two to six days. Untreated horses will develop abscessed lymph nodes which open and drain within one to two weeks after the onset of the disease. Although most horses recover, about 10 percent of untreated horses die. Death most commonly occurs due to a secondary infection causing pneumonia. While uncommon, it is usually fatal.
Treatment depends on the stage of the disease.
A veterinarian can take nasal swabs to confirm that the horse is not shedding streptococcus equi. However, because the bacteria can be shed sporadically, a total of three nasal swabs over a period of seven days are required to assure that the horse is negative. Vaccinations are another useful control. Although current vaccines are more effective and cause less reaction than those of the past, they do not always prevent the disease. Still, the severity of the disease is lessened if the horse has received the inoculation.