Pyrethroid-Resistant and Susceptible Triatoma infestans (Klug, 1834) (Hemiptera, Triatominae): Analysis of Their Vectorial Characteristics by Metacyclogenesis, Feeding/Defecation Patterns, and Parasite Load

Abstract

Populations of Triatomas infestans with different susceptibility to pyrethroid insecticides were reported to have distinct evolutionary and epidemiological characteristics. We aimed at evaluating metacyclogenesis and parasite load as measures of vector competence and feeding/defecation patterns as vectorial capacity estimates of a group of resistant (“R”) and susceptible (“S”) T. infestans. Third instar nymphs of each group were fed on mice infected with Trypanosoma cruzi (Tulahuén strain, DTU VI). Parasite concentration in blood was quantified by real-time PCR (qPCR) for each mouse. The time at which feeding started, the span of feeding, the volume of blood consumed, and the time taken to defecate were measured. At 30 days post-feeding, feces were analyzed in parallel by optical microscopy (percentage of metacyclic trypomastigotes, % MT), and qPCR (total T. cruzi DNA). The ratio of parasites consumed/defecated by nymphs of each group was used to estimate the parasites’ survival and multiplication inside the triatomines’ gut. It was estimated that for each blood trypomastigote consumed, 6.6 parasites were obtained in the feces of “R” nymphs, and 7.9 in “S”. “R” nymphs consumed a higher volume of blood, had lower % MT in their feces (lower vectorial competence), and took longer to defecate (lower vectorial capacity) than “S”.