Residual insecticide spraying with deltamethrin PM 5% has been a cornerstone strategy used in the Chagas disease Control Program in the región of Arequipa. Nonetheless, Trypanosoma cruzi natural infected synan- thropic rodents are not used as an indicator to evalúate interruption of vector transmission. The objective was to determine the natural infection Índex by T. cruzi in the synanthropic rodent, Rattus rattus, before and after household residual insecticide spraying with deltamethrin PM 5%, as impact indicator for Chagas disease vector control strategies. A quasi-exper- imental study was performed in the rural locality of Murco (Caylloma, Arequipa), through capture of rodents during household pre-spraying stage and capture of rodents during the post-spraying stage. One xenodiagnosis box was used in each animal containing 10 nymphs III of Triatoma infestans. The rodent's identified was Rattus rattus and the infection Índex for the hemoflagellate identified as Trypanosoma cruzi, was 84.2% in the pre-spraying stage and 0% in the post-spraying stage. Furthermore, 50% (2/4) of Mus musculus were positive in the pre-spraying stage. It is concluded that the negativization of R. rattus in the post-spraying stage could indícate a remarkable transmission reduction or interruption of T. cruzi vector transmission inthe locality of Murco.