[Importance of the method for obtaining feces from triatominae in the assessment of triatomine susceptibility to Trypanosoma cruzi].

Two patients on the acute phase of Chagas' disease were submitted to xenodiagnosis examination with different species of triatomine bugs, in order to study bug susceptibility to Trypanosoma cruzi. Species used were Dipetalogaster maximus, Rhodnius neglectus, R. prolixus, R. robustus, Triatoma infestans and T. rubrovaria. Both the number of infected bugs, and the number of excreted trypanosomes by bug, were used as parameters for evaluation of species susceptibility. Xenodiagnosis reading was performed by two methods, the classic abdominal compression and the spontaneous dejection method; this was more efficient than the former in relation to the number of parasites per wet smear (by Wilcoxon test). When susceptibility was evaluated by the number of infected bugs, in one of the patients all D. maximus and R. neglectus became infected (100%), 95% of R. robustus, 90% of R. prolixus and T. rubrovaria, and 85% of T. infestans. When evaluation was performed through the number of excreted parasites in this patient with reading by abdominal compression, the higher susceptibility was with R. neglectus, followed by R. prolixus, D. maximus and R. robustus, T. infestans and T. rubrovaria; reading by spontaneous dejection yielded better results for D. maximus and R. prolixus followed by T. rubrovaria, R. robustus, T. infestans and R. neglectus. For the other patient susceptibility evaluated by the number of excreted parasites was similar by both reading methods and did show the same susceptibility pattern (R. neglectus and then T. rubrovaria and T. infestans), but the number of excreted trypanosomes was much higher by the spontaneous dejection method.