COMPARISON OF THE POLYMERASE CHAIN-REACTION WITH 2 CLASSICAL PARASITOLOGICAL METHODS FOR THE DIAGNOSIS OF CHAGAS-DISEASE IN AN ENDEMIC REGION OF NORTH-EASTERN BRAZIL

The sensitivities for Chagas disease diagnosis of haemoculture, xenodi agnosis, and polymerase chain reaction (PCR) amplification of Trypanos oma cruzi kinetoplast deoxyribonucleic acid (DNA) were compared for 10 1 patients living in an endemic region who were serologically positive for T. cruzi. PCR gave 60 positive results (59.4%), while a haemocult ure was positive in 26 cases (25.7%) and xenodiagnosis in 36 (35.6%). Four xenodiagnosis-positive but PCR-negative patients were examined in detail. The discrepancies were not due to inhibition of the PCR react ions, as the samples were used successfully to amplify a human sequenc e. Nor were they due to a variation in kinetoplast DNA sequences, as t he kinetoplast DNA of the parasite strains isolated from these patient s after xenodiagnosis gave rise to the expected product when amplified by the PCR. We concluded that no parasite was present in the 5 mL of blood used for PCR, while probably a single T. cruzi cell was present in the blood volume ingested by the insects during xenodiagnosis (abou t 3 mL). This suggests that the total blood quantity collected for the PCR may be important with patients with low parasitaemia.