BACKGROUND: Sylvatic populations of Triatoma infestans represent a challenge for vector control as these populations are not targeted by control activities and could play a key role in post-spraying house re-infestation. Improved understanding of sylvatic foci, population distribution, dispersion patterns, gene flow between sylvatic and domestic populations, as well as characterization of insecticide resistance profiles, is crucial to optimize vector control interventions.
METHODS: We analyzed the genetic relationship of five Andean populations from Bolivia from localities with distinct insecticide susceptibility profiles (sylvatic: 20 de Octubre, Illicuni, Kirus Mayu and Mataral and one domestic from Mataral). Individual multilocus genotypes based on 8 microsatellites and the DNA sequence of a fragment of the cytochrome B (cytB) gene were obtained for 92 individuals. We compared the cytB haplotypes with previously reported Andean T. infestans haplotypes and evaluated the directionality and possibly history of gene flow among populations. Each specimen was screened for 2 nucleotide mutations (L1014 and L9251) of the sodium channel gene (kdr), described for T. infestans and related to pyrethroid resistance.
RESULTS: Significant genetic differentiation was observed among all populations, reflecting current genetic isolation among them. However, individuals of admixed origin were detected in four populations, especially between the sylvatic and domestic populations from Mataral. Historical analysis of gene flow suggests that insecticide resistance is conferred by ancient trait(s) in T. infestans sylvatic populations that are capable of invading domiciles. The kdr mutation L1014 was identified in one individual from Mataral, while the L9251 mutation was not detected in any population. The low frequency of kdr mutations in these populations suggests this mechanism is unlikely to be the primary cause of the observed altered insecticide susceptibility. However, the resistance conferring mutation is present in the area and with the potential to be selected under insecticidal pressure.
CONCLUSIONS: These results emphasize the need for stronger entomological surveillance in the region, including early detection of house invasion, particularly post-spraying, monitoring for resistance to pyrethroids and the design of integrative control actions that consider both sylvatic foci around domestic settings as well as the bug dispersion dynamics.