Bartonella spp. infection in healthy and sick horses and foals from the southeastern United States.

BACKGROUND Bartonella species bacteremia has been identified in numerous animal species. These bacteria cause, or have been associated with, a spectrum of clinical manifestations in dogs and human patients. The frequency of exposure to or infection with Bartonella spp. among healthy and sick horses has not been reported. OBJECTIVE To test healthy and sick horses and sick foals from the southeastern United States for serological, microbiological, and molecular evidence of Bartonella infection. ANIMALS Forty-seven healthy horses, 15 sick foals, 22 horses with musculoskeletal manifestations, and 8 horses with colic were tested for Bartonella. METHODS IFA serology and PCR before and after BAPGM (Bartonella alpha-Proteobacteria Growth Medium) enrichment blood culture. RESULTS Bartonella antibodies were not detected in foals or horses. Three Bartonella species, B. henselae, B. vinsonii subsp. berkhoffii (genotypes I and III), and a Bartonella species with closest homology to Candidatus Bartonella volans, were PCR-amplified and sequenced from blood or BAPGM enrichment blood culture samples from 1/47 healthy horses, 3/15 sick foals, 5/22 horses with musculoskeletal disease, and 0/8 horses with colic. CONCLUSIONS AND CLINICAL IMPORTANCE Horses in the southeastern United States are naturally infected with B. henselae, B. vinsonii subsp. berkhofii genotypes I and III, and a bacteria most similar to Candidatus Bartonella volans. Antibodies were not detectable by indirect fluorescent antibody assay (IFA) testing in bacteremic foals or horses, and prolonged enrichment culture for periods up to 21 days were necessary to document bacteremia in most horses. Further investigation into the pathogenic potential of Bartonella spp. infection in horses is warranted.