Caracterização fenotípica e estimativa da reatividade cruzada de cepas de Streptococcus equi isoladas de equinos da região Sul do Rio Grande do Sul

Abstract

Streptococcus equi is the causative agent of strangles, one of the most widespread and costly horse diseases. The disease is highly contagious, and common symptoms are fever and lynphadenitis with abscesses in the neck region. Vaccines against strangles have been used but do not confer efficient protection against infection with Streptococcus equ i. In this paper, Strains of Streptococcus equi recovered from thirty-five horses with clinical Strangles in southern Rio Grande do Sul, Brazil, were characterized. Monovalent inactivated vaccines were produced with the strains. Groups of isogenic Balb/c mice were vaccinated on days 0 and 14 with the vaccines and with two commercial vaccines for strangles. Blood samples were collected on days 0, 14, 28, 56 and 70. Antibodies were titrated through ELISA using homologous and heterologous antigens, and Cross Reactivy Indices estimated. Thirteen strains of S. equi were recovered from the thirty-five samples studied. Five of them produced acid from some of the carbohydrates used, behaving as atypical strains. Four of these only metabolised the carbohydrate when equine serum was added. Cross Reactivity Indices showed that the strains studied belonged to the same serogroup. Cross Reactivity Indices among the strains recovered and the vaccines, on the contrary, varied from 23 to 46, showing very low reactivity among them.