Where do these bugs come from? Phenotypic structure of Triatoma infestans populations after control interventions in the Argentine Chaco

Abstract

House re-invasion by native triatomines after insecticide-based control campaigns represents a major threat for Chagas disease vector control. We conducted a longitudinal intervention study in a rural section (Area III, 407 houses) of Pampa del Indio, northeastern Argentina, and used wing geometric morphometry to compare pre-spray and post-spray (re-infestant bugs) Triatoma infestans populations. The community-wide spraying with pyrethroids reduced the prevalence of house infestation by T. infestans from 31.9% to < 1% during a four-year follow-up, unlike our previous studies in the neighbouring Area I. Two groups of bug collection sites differing in wing shape variables before interventions (including 221 adults from 11 domiciles) were used as a reference for assigning 44 post-spray adults. Wing shape variables from post-spray, high-density bug colonies and pre-spray groups were significantly different, suggesting that re-infestant insects had an external origin. Insects from one house differed strongly in wing shape variables from all other specimens. A further comparison between insects from both areas supported the existence of independent re-infestation processes within the same district. These results point to local heterogeneities in house re-infestation dynamics and emphasise the need to expand the geographic coverage of vector surveillance and control operations to the affected region.

Beating the odds: Sustained Chagas disease vector control in remote indigenous communities of the Argentine Chaco over a seven-year period

“…Several pieces of evidence do not support that the remaining post-spraying infestations originated from residual foci: pre-spraying and post-spraying infestations were not significantly associated, unlike in Areas I and II [ 37 , 38 ]; wing shape analyses of T . infestans populations from Area III indicated the post-spraying foci were more likely related to external sources (not within Area III) than to baseline populations, with a low rate of exchange between Area III and Area I triatomines [ 41 ]; the protracted time gap between pre- and post-spraying foci at the same house, and the stage distribution and abundance of post-spraying foci (mainly including incipient bug colonies with a few adults and early-instar nymphs). Peripheral or sylvatic sources of T .…”

“…Substantial population structuring in T . infestans [ 41 , 82 , 83 ] may also contribute to explain household-level variations in resistance status [ 84 ]. Therefore, the combination of several factors may help explain the heterogeneous impact of the same intervention protocol among Pampa del Indio study areas.…”

“…Two of the rural sections were mainly inhabited by an indigenous people (Qom) that displayed intense residential mobility, especially within Area III [ 40 ]. Unexpectedly, the intervention there exerted immediate impacts on house infestation as revealed by timed-manual searches; the few foci detected after blanket insecticide spraying were mainly assigned to external sources as determined by wing geometric morphometry [ 41 ]. Identifying processes and mechanisms underlying the successful vector control status achieved in Area III is relevant to the goals of suppressing the major vectors of Chagas disease and interrupt domestic transmission, in concert with the Sustainable Development Goals and the London’s Declaration on NTDs [ 42 ].…”

Morphometric Wings Similarity among Sylvatic and Domestic Populations of Triatoma infestans (Hemiptera: Reduviidae) from the Gran Chaco Region of Paraguay

“…This differentiation could also be attributed to the diversity of construction materials, variety of hosts, infestation before insecticide spraying, as explained elsewhere and were mentioned as explicative factors in independent studies. 24 , 42 Furthermore, other reasons could be related to the geographical distance between these two villages of 15 km that could be showing a certain structuring caused by geographical distances, 20 , 43 or by subsequent domiciliary sprayings, 21 which allow the differentiation of their different backgrounds.…”

Effectiveness of Large-Scale Chagas Disease Vector Control Program in Nicaragua by Residual Insecticide Spraying Against Triatoma dimidiata

“…For instance, a morphometric study in Chaco Province of Argentina suggested that reinfestant T. infestans came from external sources because they were significantly different from the pretreatment vector population. 35 Similar studies should be encouraged for improving understanding of the reinfestation pattern of T. dimidiata. Figure 4, although our data are patchy because of the limited number of communities investigated, shows that the communities where reinfestation was confirmed are not uniformly distributed.…”