Dangerous Strangles

Strangles, the upper respiratory disease in horses caused by Streptococcus equi, has a low mortality rate (2.6%), but it is highly contagious and spreads rapidly. Complications can occur in as many as 20% of cases. One such complication, called purpura hemorrhagica (PH), is the result of an overzealous immune response to S. equi by the horse's body. A report from the University of Minnesota Veterinary Medical Center published recently in the Journal of the American Veterinary Medical Association details five cases of a particularly serious form of PH.

In classic PH, which can be triggered by an immune reaction to bacteria, viruses, or even certain drugs, there are tiny, pinpoint, petechial (spotted) hemorrhages along the mucous membranes as well as areas of firm, pitting edema (swelling) on the lower abdomen and lower limbs. Affected horses tend to have abdominal pain, a high white blood cell (WBC) count, and a mild increase in the muscle enzymes creatine kinase (CK) and aspartate transferase (AST).

All five cases had experienced S. equi infection and noticeable differences in clinical signs. Their abdomens, chests, and upper limbs had edema of the muscle and surrounding supportive tissues instead of edema beneath the skin, and the surrounding muscles were very painful and stiff. Bloodwork revealed an elevated WBC count and a markedly elevated CK and AST. Four horses were euthanatized. Blood clots, or "infarcts," were found in intestinal blood vessels, severe hemorrhage was seen in the limbs, lungs, chest, and abdomen, and S. equi abscesses were found in each case. One horse survived after a one-week hospital stay and 13 weeks of corticosteroids.

Heather Kaese, DVM, MS, Dipl. ACVIM, lead author on the study, said, "If your horse has been vaccinated or sick with strangles and begins to show edema of the limbs, call your veterinarian immediately. Early diagnosis (of an infarctive case) through bloodwork and early aggressive treatment with corticosteroids is imperative for a successful outcome."

About the Author

Susan Piscopo, DVM, PhD

Susan Piscopo, DVM, PhD, is a free-lance writer in the biomedical sciences. She practiced veterinary medicine in North Carolina before accepting a fellowship to pursue a PhD in physiology at North Carolina State University. She lives in northern New Jersey with her husband and two sons.

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