Babesia gibsoni infection among dogs in the southeastern United States

Objective - To identify subclinical Babesia gibsoni infection in American Pit Bull Terriers from the southeastern United States and to determine the genetic sequence of parasite DNA isolated from these dogs. Design - Case series. Animals - 33 American Pit Bull Terriers and 87 dogs of various other breeds. Procedure - Blood smears were examined for microscopic evidence of the parasite, and DNA was extracted from blood samples and used in a polymerase chain reaction (PCR) assay designed to amplify the small subunit ribosomal RNA gene sequence of B gibsoni. Amplification products of the expected size were sequenced, and sequences were compared with published sequences for B gibsoni isolates. Hematocrit, platelet count, mean platelet volume, WBC count, and eosinophil count were compared between dogs with positive PCR assay results and dogs with negative results. Results - Results of the PCR assay were positive for 18 of the 33 (55%) American Pit Bull Terriers, including all 10 dogs with microscopic evidence of parasitemia. Only 1 of these dogs was clinically ill at the time blood samples were collected. Results of microscopic evaluation of blood smears and of the PCR assay were negative for the 87 other dogs. Hematocrit and platelet count were significantly lower in dogs with positive PCR assay results than in dogs with negative results. Conclusions and Clinical Relevance - Results suggest that American Pit Bull Terriers in the southeastern United States may be subclinically infected with B gibsoni. However, subclinical infection was not identified in dogs of other breeds from the same geographic area.