Upper-respiratory infections caused by Strep, such as strangles, are as bad as human strep throats, if not worse. Worse yet are the possible complications.
Strep infections in people can affect the whole body, causing arthritis, skin damage, heart damage or kidney damage. In horses, a severe strangles infection can result in Strep abscesses developing deep in the lungs or abdomen. It can also become seated in the gutteral pouches, where it may cause a prolonged problem with respiratory difficulty, even abnormal breathing noises, although the horse may not have a telltale nasal discharge.
If the infection makes its way to the bloodstream, abscesses can form in virtually any organ, and circulating bacterial proteins can precipitate out in the blood vessels to cause an inflammatory reaction in the kidneys, joints or skin. Clotting abnormalities may also develop.
They may also develop purpura hemorrhagica, a syndrome of severe lower leg swelling from vascular damage and the development of small hemorrhages visible in the mucus membranes such as gums and lining of the vagina. Older horses, or horses that have been vaccinated for strangles, may have few or no respiratory symptoms but develop purpura or joint swellings.
Strict isolation of all incoming horses is the first step in preventing an outbreak. The decision regarding whether or not to vaccinate your horses needs to be made by your veterinarian.
While enlarged lymph nodes and white/yellow/orangish heavy nasal discharge leave little doubt there is a strangles infection, a culture of at least one affected horse is advisable to confirm the diagnosis. It will also ensure the chosen antibiotics are effective against that strain. If leg or joint swelling develops without nasal discharge or abscess drainage for culturing, the horse can be tested for strangles antibodies by an ELISA test. This test can distinguish between antibody levels from vaccination or remote exposure and those noted during recent infection and purpura.
Most Strep bacteria are sensitive to penicillin and penicillin derivatives, like ampicillin or amoxicillin. Debates rage regarding whether strangles horses should be treated or the abscesses allowed to form a head and then drain. The attending veterinarian decides whether to treat or not but, given the severity of possible complications, it’s reasonable to start antibiotics for a horse that remains severely depressed and off feed for more than just a few days.
The major mistake made when using antibiotics is usually not continuing them long enough. A minimum of 10 to 14 days is required. If purpura develops, the gold standard in treatment is corticosteroids. Avoiding steroids could result in extensive damage, even death. In fact, the combination of antibiotics and steroids is a good idea to kill remaining organisms that might fuel the reaction and to guard against reinfection while the immune system is depressed.