The invention relates to a recombinant DNA and polypeptide sequence of an immuno-dominant phage particle associated protein from Bartonella bacilliformis. The recombinant protein is easily produced permitting the conduct of more accurate and rapid diagnositic assays for the detection of B. bacilliformis infection with reduced reagent and equipment requirements over that required by currently available methods of diagnosis. The DNA and polypeptide sequence is also useful in vaccine preparations against B. bacilliformis.