COMPARISON OF PCR AND MICROSCOPIC METHODS FOR DETECTING TRYPANOSOMA-CRUZI

The diagnosis of acute infection with Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease, is generally made by detecting parasites by microscopic examination of fresh blood, Although highly s pecific, this approach often lacks sensitivity, Several years ago, PCR assays for the detection of T. cruzi were described, but the sensitiv ities and specificities of these tests have not yet been defined preci sely. In the present study, we first compared the sensitivities of PCR methods that differ in sample processing as well as in the target seq uences that are amplified. Then, we challenged eight mice with T. cruz i, and on 31 days over a 380-day period, we compared the ability of th e PCR method with the highest sensitivity to detect parasites in blood with that oil microscopic examination. During the acute phase of the infections, parasites were detected on average 3.9 days earlier by the PCR method than by microscopy. Furthermore, the infected mice were co nsistently positive by the PCR method during the chronic phase, while parasites were intermittently detected by microscopic examination duri ng that period. Overall, among the 248 comparisons, in 84 the PCR meth od was positive and no parasites were seen by microscopic examination, whereas the reverse was true in only 1 case, a difference that is hig hly significant, These findings suggest that this approach should be u sed in patients suspected of having acute Chagas' disease. Moreover, t he higher sensitivity of the PCR method observed in both the acute and chronic phases of the T. cruzi infections in the mice that we studied indicates that this approach should be useful in evaluating experimen tal drugs in T. cruzi-infected laboratory animals.