Date Published: August 02, 2017
Publisher: The American Society of Tropical Medicine and Hygiene
Author(s): Antonieta Rojas de Arias, Ana Laura Carbajal de la Fuente, Ana Gómez, María Carla Cecere, Miriam Rolón, María Celeste Vega Gómez, Cesia Villalba.
Despite sustained efforts for eliminating Triatoma infestans, reinfestation still persists in large part of the endemic area of Chagas disease from the Gran Chaco region. Sylvatic T. infestans populations seem to threat success of control programs of domestic T. infestans. In this study, we analyze whether T. infestans collected after a community-wide spraying were survivors or were immigrants from elsewhere using geometric morphometric tools. We used 101 right wings of female T. infestans captured before and after intervention program carried out in 12 de Junio and Casuarina, villages from Paraguayan Chaco, and in Puerto Casado during presprayed collection. There were no significant differences in wing size of domestic T. infestans between pre- and postspraying populations, and between domestic and sylvatic ones. When shape variables originating from postintervention individuals from 12 de Junio were introduced one by one into a discriminant analysis, the greatest weight (53%) was allocated to the sylvatic group. Furthermore, from the prespraying population, 25% were reallocated as postintervention individuals. Only 11% of the insects were reassigned to other groups Puerto Casado and Casuarina. These results suggest that postspraying individuals appear to have different origins. Half of the postspraying individuals from 12 de Junio were similar to the sylvatic ones and 25% of these were similar to those captured in the prespraying period. This remarkable morphometric wings similarity between sylvatic and domestic populations is new evidence suggesting that they could be highly related to each other in the Paraguayan Chaco; human-fed bugs from sylvatic area also support this.
The Gran Chaco eco-region and adjacent areas extending from Argentina, Bolivia, and Paraguay are highly endemic for Chagas disease. Despite the current campaigns for the elimination of the major vector Triatoma infestans (Hemiptera: Reduviidae), transmission and reinfestation persist in wide areas of this region.1 This fact interrupts the success in eliminating vectorial transmission because control programs have been conducted against domestic populations of T. infestans using residual insecticide spraying of human dwellings,2 and did not involve the potential reinfestation process from sylvatic areas.3,4 Therefore, this new epidemiological scenario is a priority issue for the Southern Cone Initiative.1,5
Our study seems to be the first to evaluate wings similarity of T. infestans from the neighboring wild environment using geometric morphometric tools and shows a remarkable morphometric wings similarity between sylvatic and domestic populations and has suggested potential evidences on active dispersal ability and migration of these sylvatic individuals. Our results revealed that when the intradomicile postspraying individuals from 12 de Junio were entered one by one to the discriminant analysis, most were assigned to the sylvatic group. An entomological survey was conducted in all dwellings of 12 de Junio and Casuarina, resulting in a significant T. infestans infestation. However, in the entomological monitoring of postspraying at 3, 6, 9, and 12 months, very low triatomine abundance per house was detected, mostly adults inside the dwellings, because in these villages peridomestic structures did not exist. With the support of a trained dog, a search of sylvatic areas around 12 de Junio was performed 2 years after the spraying, which allowed us to capture sylvatic individuals of T. infestans for the first time in the Paraguayan Chaco. These sylvatic triatomines were genetically similar to those found in domiciles, as well as those captured in the monitoring postspraying.12,13 Unlike what was observed by us, previous studies in Argentina and the eastern region of Paraguay have attributed the reinfestation by T. infestans after spraying to residual foci in peridomestic structures.18,26,39 However, in the absence of peridomestic structures in the localities of our study area, with the exception of three dwellings in Casuarina, triatomines collected during postspraying periods may have been residual, sylvatic, or brought by passive transportation.