Evaluation of chemotherapy with benznidazole and nifurtimox in mice infected with Trypanosoma cruzi strains of different types.

A test was made of the susceptibility of 30 strains of Trypanosoma cruzi to chemotherapy with nifurtimox (Bay 2502) and benznidazole (Ro 7-1051). The strains had previously been classified as type I, II, or III according to their morphobiological and isoenzymic characteristics. Three type I strains, 14 type II strains, and 13 type III strains were studied. Mice were infected with 2 x 10(5) blood forms of these parasites and treated for 90 days with benznidazole or nifurtimox. All the surviving mice were submitted to parasitological tests (direct parasitaemia, xenodiagnosis, inoculation in new-born mice, and haemoculture) and serological tests (indirect immunofluorescence). As the latter remained positive in about 80% of the parasitologically negative animals, the cure rates were based on the more reliable parasitological tests. Type I strains displayed high susceptibility, type II strains showed medium to high susceptibility, and type III strains were highly resistant to both drugs. The fact that a particular strain type, with its own level of susceptibility, usually predominates in a given geographical area may explain the contradictory results after chemotherapy from different endemic areas.