Antibody to the Dirofilaria immitis aspartyl protease inhibitor homologue is a diagnostic marker for feline heartworm infections

Feline heartworm disease, caused by the filarial nematode Dirofilaria immit is, has been diagnosed with increased frequency in areas endemic for canine heartworm infection. The routine methods for determining the infection sta tus of dogs, such as identification of circulating microfilariae in blood o r identification of circulating antigen in serum, plasma or blood, have pro ven inadequate for screening cats. The inadequacies are due to the likeliho od of single-sex infections and clinical disease during prepatent infection s. Current antibody detection methodologies rely on crude or partially puri fied worm antigen preparations that may result in poor specificity. This re port describes the cloning, expression, and diagnostic utility of the D. im mitis homologue (PDi33) of the Onchocerca volvulus aspartyl protease inhibi tor (Ov33). PDi33 is present in all stages that occur in the mammalian host (microfilariae, L3, L4, adult males, and females) and is released by adult s cultured in vitro. An indirect enzyme-linked immunosorbent assay (ELISA) using antibody to recombinant PDi33 as a diagnostic marker for infection in cats was very sensitive and was useful for identifying prepatent infection s. Testing of sera from cats infected with common gastrointestinal parasite s also indicated excellent specificity. The same ELISA in dogs, although de monstrating reasonable sensitivity and specificity, appeared to be of less value as compared with the currently accepted antigen detection methodologi es.