Dynamics of Sylvatic Chagas Disease Vectors in Coastal Ecuador Is Driven by Changes in Land Cover

Abstract

BackgroundChagas disease is a serious public health problem in Latin America where about ten million individuals show Trypanosoma cruzi infection. Despite significant success in controlling domiciliated triatomines, sylvatic populations frequently infest houses after insecticide treatment which hampers long term control prospects in vast geographical areas where vectorial transmission is endemic. As a key issue, the spatio-temporal dynamics of sylvatic populations is likely influenced by landscape yet evidence showing this effect is rare. The aim of this work is to examine the role of land cover changes in sylvatic triatomine ecology, based on an exhaustive field survey of pathogens, vectors, hosts, and microhabitat characteristics' dynamics.Methodology and Principal FindingsThe study was performed in agricultural landscapes of coastal Ecuador as a study model. Over one year, a spatially-randomized sampling design (490 collection points) allowed quantifying triatomine densities in natural, cultivated and domestic habitats. We also assessed infection of the bugs with trypanosomes, documented their microhabitats and potential hosts, and recorded changes in landscape characteristics. In total we collected 886 individuals, mainly represented by nymphal stages of one triatomine species Rhodnius ecuadoriensis. As main results, we found that 1) sylvatic triatomines had very high T. cruzi infection rates (71%) and 2) densities of T. cruzi-infected sylvatic triatomines varied predictably over time due to changes in land cover and occurrence of associated rodent hosts.ConclusionWe propose a framework for identifying the factors affecting the yearly distribution of sylvatic T. cruzi vectors. Beyond providing key basic information for the control of human habitat colonization by sylvatic vector populations, our framework highlights the importance of both environmental and sociological factors in shaping the spatio-temporal population dynamics of triatomines. A better understanding of the dynamics of such socio-ecological systems is a crucial, yet poorly considered, issue for the long-term control of Chagas disease.

Bottlenecks in domestic animal populations can facilitate the emergence of Trypanosoma cruzi , the aetiological agent of Chagas disease

“…Documentamos con precisión este escenario, en el cual los cuellos de botella en la población de cuyes llevan a una alta prevalencia de T. cruzi en las poblaciones de insectos triatominos, y por último intensifican el riesgo de enfermedad de Chagas en los hogares. Fuera de los Andes, el papel de los cuyes (y de roedores en general) en la transmisión doméstica de T. cruzi es probablemente menor [36] (ver [37]). Las dinámicas que describimos—incluyendo la concentración de vectores en un número limitado de animales hospederos, son comunes.…”

Trypanosoma cruzi population dynamics in the Central Ecuadorian Coast

“…In Southern Ecuador (Loja) and the North of neighboring Peru, R. ecuadoriensis has been shown to colonize human dwellings [18, 29] as well as being present in sylvatic environments [19–21]. Morphometric analysis suggest that two distinct R. ecuadoriensis population sexist in Southern Ecuador, one in sylvatic and another in domestic/peridomestic habitats [30].…”

“…The panel included samples collected in Manabi province in domestic (within domiciles) or peridomestic habitats (near human dwellings or associated with human activities such as chicken coops, piles of construction material or wood, stones, bricks, piles of agricultural products, and other structures, as described in [18]). Additionally, samples came from triatomines which were collected in sylvatic habitats (at least 20 meters away from human domiciles) by manual searches following procedures described in [19], or in quadrants as previously described in [20, 21]. …”

Distribution of triatomine species in domestic and peridomestic environments in central coastal Ecuador

“…cruzi [7,8]. Sylvatic populations have been found in association with squirrel nests ( Sciurus nebouxii , previously known as Sciurus stramineus )[7,9,10, 31], the endemic palm Phytelephas aequatorialis [3] and other plant species [9]. …”