Retrospective evaluation of the epidemiological importance of Triatoma infestans and Panstrongylus megistus in the transmission of Trypansoma cruzi in a region of southeastern Brazil.

Panstrongylus megistus is the most important autochthonous vector of Trypanosom cruzi, the etiological agent of Chagas disease, in the midwest region of the Minas Gerais State, Brazil. This study investigates the vectorial roles of Triatoma infestans and P. megistus in Chagas disease in this geographical area during the late 1970s. A retrospective analysis of entomological and serological surveys from 1975-1983 was conducted, comparing the presence of T. infestans and P. megistus with the seroprevalence of T. cruzi infection in the human population within the Divinopolis Regional Health Superintendency. Panstrongylus megistus was recorded in all surveyed municipalities (52/52), whereas T. infestans co-occurrence with P. megistus was recorded in only 19.2% (10/52) of them. In the 41 municipalities where only P. megistus was found and relevant data were available, the mean seroprevalence of human T. cruzi infection was 17.8% ranging from 1.0% to 41.9%. In the municipalities where T. infestans occurred, the mean seroprevalence was higher, at 25.8%, ranging from 9.8% to 40.8%. Among the municipalities where only P. megistus was present, 19.5% had a low, 29.3% an intermediate, and 51.2% a high seroprevalence of human T. cruzi infection. In the ten municipalities where both T. infestans and P. megitus were found, 80% showed high seroprevalence, whereas only one municipality each showed low or intermediate levels. The findings highlight the significant role of P. megistus in T. cruzi transmission, even in the absence of T. infestans. The wide distribution of P. megistus increased the risk of transmission. P. megistus was the main household vector in the region in the 1970s. Nowadays, continuous surveillance remains essential for monitoring triatomine infestations and evaluating the current risk of T. cruzi transmission.