RESUMEN
The present study deals with the evaluation of the effectiveness of the measures employed in the control of triatoma infestans, the vector of trypanosoma cruzi infection (Chagas' disease), in the IV Region of Chile through a serological follow up program. For this reason, a serological survey has been carried out in 2,783 chidren, from 0 to 10 years, who live in rural high endemic areas of the region. The sera were tested using an indirect hemagglutination test (IHAT) and ELISA techniques with results agreeing in 99,9 for percent of the samples. In children with positive serology xenodiagnosis was perfomed and blood samples from the corresponding mothers were submitted to serology for Chagas's disease. These addicional tests should allow to distinguish between congenital infection and vectorial transmission. It was observed that vectorial transmission of T. cruzi was interrupted in some localities where entomological control has been applied for 10 years, or lowered in those which have been submitted to desinsectations in the last 5 years. On the other hand, a relatively high prevalence of the infection has been detected in some localities. These results suggest an apparent increase of vectorial transmision, indicating the need of readjusting the dwellings insecticide sprayings activities to improve the measures against the vector