Some horses recover from the acute phase only to have the organism remain in the guttural pouch for months afterward. These horses may be the source of new infections. Research into new outbreaks in the US suggests this is rare however. Newton et al. in Newmarket England have found that guttural pouch carriers may be undetectable for several months by culture of nasal swabs. Shedding of S. equi may resume later and continue sporadically. The only reliable means of identifying these carriers is endoscopic examination to confirm empyema and/or chondroids and to sample pouch content, though this not very practical. It has shown that PCR on the nasal secretions combined with culture greatly increases the carrier detection rate, but that long-term carriers may remain PCR positive for months after viable organisms are no longer cultured suggesting that DNA persists for some time in the guttural pouch following death of S. equi.See below for treatment.

Though with good care it is rare, Strangles can infect focal areas of the body and create abscesses that will enlarge and eventually rupture, dissemination organisms throughout the body. This can occur weeks to months following recovery from the upper respiratory condition. If these abscesses are internal, they may not be readily obvious. Some of the symptoms you might see are: chronic or recurrent fever, colic, jaundice, weight loss, and generalized poor doing. Further support of the diagnosis can be made with blood work particularly: CBD, fibrinogen, and serology for S. Equi antibody.

This is an autoimmune vasculitis that is usually associated with Strangles infection and vaccination. Circulating complexes of the horses antibodies and the foreign antigens deposit into the capillaries of the leg and then stimulate an immune response. Swelling in the legs can vary from mild to severe with fever and pain typical. . Usually hemorrhages on the mucous membranes also occur. Diagnosis is based on clinical signs and a recent history of Strangles or Strangles vaccination exposure in the last 2 to 4 weeks. Vaccinating horses that already have high levels of circulating antibodies is probably associated with an increase in this problem. For this reason it may not be recommended to vaccinate a horse with a recent known Strangles infection. Any immune stimulating event that is followed with these clinical signs should raise the suspicion level for this disorder. On clinical pathology generally the only abnormality detected is a hyperfibrinogenemia but otherwise is nonspecific. This may help separate this from other causes of swollen painful legs, ...more.

There has recently been reported a infarctive form of purpura where horses who had been exposed in the prior 3 weeks to Strangles or Strangles vaccination. Instead of inducing swollen hot painful legs blood vessels, in this form the vessels become clogged (infarcted) and cause colic and muscle swelling with pain. Common hematologic and serum biochemical abnormalities included neutrophilia with a left shift and toxic changes, hyperproteinemia, hypoalbuminemia, and high serum creatine kinase and aspartate transferase activities. Early recognition of focal muscle swelling, abdominal discomfort, neutrophilia, hypoalbuminemia, and high serum creatine kinase activity combined with antimicrobial and corticosteroid treatment may enhance the likelihood of a successful outcome.