A health index to evaluate clinically a beta-hemolytic streptococcal infectious disease model in the horse

Standardization of an experimental disease model of Streptococcus zooepidemicus in the equine

A reproducible experimental disease model in horses using Streptococcus zooepidemicus was developed. An intravenous challenge dose of 1 X 10(10) colony-forming units (CFU), followed 24 h later with another challenge of 1 X 10(8) CFU of Strep. zooepidemicus produced the desired disease model. The disease was characterized by depression, pyrexia, anorexia, abnormal lung sounds, inflammation of joints, moderate to severe lameness, gradual loss of condition and emaciation. The effects of the disease on hematology, serum chemical profile and different protein fractions were studied. The disease state had no effect on serum glucose, sodium, potassium, chloride, urea nitrogen, creatinine, uric acid, calcium, phosphorus and enzymes SGOT or SGPT. However, the alkaline phosphatase showed a gradual decline. The serum iron levels dropped markedly and remained low to the last day of observations (post-infection day, PID 13). On serum protein electrophoresis, the albumin showed a gradual decrease; whereas, alpha II, beta and gamma globulin levels rose suggesting an immune response. The elevation of rectal temperatures and white blood cell counts related well with clinical observations. The serum iron levels proved very helpful in predicting the severity of clinical signs and often dropped before the onset of clinical signs and pyrexia.