Submitted to: Journal of Clinical Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/7/1999
Publication Date: N/A
Citation: Interpretive Summary: The successful development of an accurate serologic assay for Babesia caballi described. This work completes the development of accurate serologic assays for the causative agents of equine piroplasmosis (Babesia equi and Babesia caballi). In addition to their accuracy, these tests are based on recombinant components, which are produced in E. coli. Therefore these reagents can be distributed internationally for standardization. Equine piroplasmosis is an exotic disease to the United States, however, infection of horses with these parasites severely restricts the international movement of horses.
Technical Abstract: A competitive inhibition ELISA (cELISA) was developed for detection of equine antibodies specific for Babesia caballi. The assay employed recombinant B. caballi rhoptry associated protein 1 (RAP-1) and monoclonal antibody (mAb) 79/17.18.5 reactive with a peptide epitope of a native 60 kDa B. caballi antigen. The gene encoding the recombinant antigen was sequenced and database analysis revealed the gene product to be a rhoptry-associated protein. Cloning and expression of a truncated copy of the gene demonstrated that mAb 79/17.18.5 reacts with the C- terminal repeat region of the protein. The cELISA was used to evaluate 302 equine sera previously tested for antibodies to B. caballi using a standardized complement fixation test (CFT). The cELISA and CFT were 73% concordant. Seventy-two of the 77 discordant sera were CFT(-)/cELISA(+). Further evaluation of the discordant sera by immunofluorescence assay demonstrated that at a serum dilution of 1:200, 48 of the CFT(- )/cELISA(+) sera contained antibodies reactive with B. caballi RAP-1. Four of 5 CFT(+)/cELISA(-) sera contained antibodies reactive with B. caballi when tested by IFA. These data show that following infection with B. caballi, horses consistently produce antibody to the RAP-1 epitope defined by mAb 79/17.18.5, and when used in the cELISA format recombinant RAP-1 is a useful antigen for the serologic detection of anti-B. caballi antibodies.