EPIDEMIOLOGIC AND IMMUNOLOGICAL CHARACTERISTICS OF STREPTOCOCCUS-EQUIINFECTION IN FOALS

A 2-phase study was performed to characterize the effects of Streptoco ccus equi infection in unexposed and previously exposed foals. In phas e I, 22 weanling foals involved in a naturally occurring S equi epizoo tic were studied, along with a comparison group of 11 unexposed foals, matched for age, sex, and breed. Six months later (phase II), an epiz ootic was experimentally induced in previously exposed and unexposed f oals from phase I. The prevalence and duration of clinical signs, the relative risk of developing disease, bacteriologic culture results, he matologic responses, and mucosal and serum immunologic responses were determined. Disease protection in phase-I and -II foals was associated with high values for serum S equi M protein-specific IgG at the onset of the epizootic (P < 0.02 for phase 1 and P < 0.01 for phase II), an d with a rapid (within 2 weeks of exposure) mucosal S equi M protein-s pecific IgG response CP < 0.05 for phase I and P = 0.01 for phase II).