Hidden danger: Unexpected scenario in the vector-parasite dynamics of leishmaniases in the Brazil side of triple border (Argentina, Brazil and Paraguay)

Abstract

Every year about 3 million tourists from around the world visit Brazil, Argentina and Paraguay´s triple border region where the Iguaçu Falls are located. Unfortunately, in recent years an increasing number of autochthonous canine and human visceral leishmaniasis (VL) cases have been reported. The parasite is Leishmania (Leishmania) infantum and it is transmitted by sand flies (Phlebotominae). To assess the risk factors favorable for the establishment and spread of potential vectors the Centers for Disease Control and Prevention light trap (CDC-light trap) collections were made in the Foz do Iguaçu (FI) and Santa Terezinha de Itaipu (STI) townships and along two transects between them. Our study determined the Phlebotominae fauna, the factors that affect the presence and abundance of Lutzomyia longipalpis and Nyssomyia whitmani, the presence of L. infantum in different sand fly species and which Leishmania species are present in this region. Lutzomyia longipalpis was the prevalent species and its distribution was related to the abundance of dogs. Leishmania infantum was found in Lu. longipalpis, Ny. whitmani, Ny. neivai and a Lutzomyia sp. All the results are discussed within the Stockholm Paradigm and focus on their importance in the elaboration of public health policies in international border areas. This region has all the properties of stable VL endemic foci that can serve as a source of the disease for neighboring municipalities, states and countries. Most of the urban areas of tropical America are propitious for Lu. longipalpis establishment and have large dog populations. Pan American Health Organization´s initiative in supporting the public health policies in the border areas of this study is crucial and laudable. However, if stakeholders do not act quickly in controlling VL in this region, the scenario will inevitable become worse. Moreover, L. (Viannia) braziliensis found in this study supports the need to develop public health policies to avoid the spread of cutaneous leishmaniasis. The consequences of socioeconomic attributes, boundaries and frontiers on the spread of diseases cannot be neglected. For an efficient control, it is essential that urban planning is articulated with the neighboring cities.

Multiscale environmental determinants of Leishmania vectors in the urban-rural context

“…It is important to note that greater diversity was expected in forest and periurban environments as presented in a previous study in the Argentinean area [ 45 ], which was probably not achieved as the sampling effort did not reach the optimal threshold of the curve. In catches from the Brazilian side in equivalent environments, the same trend was observed except in the rural environment where the authors detected higher species richness with greater sampling effort [ 29 ]. The CCA analysis allows the discrimination between species well adapted to urban environments such as Lu.…”

“…longipalpis and periurban-rural Ny. whitmani in the area of the Argentina-Brazil-Paraguay border has already been described [29,42]. The rarefaction curves suggest that the peridomestic environment in rural landscapes seems stable and homogeneous enough to make the captures representative of their phlebotomine assemblages.…”

“…longipalpis, Ny. whitmani and Mg. migonei, the ruralized periurban ecotone could act as a bridge between the domestic and forest cycles of transmission by permissive vectors [29,78], and the forested edges could be an eventual shelter for phlebotomine during chemical interventions in urban areas [79]. The modeling allowed to assess the abundance distribution of these vectors; mainly driven by NDWI, landscape structure and blood-meal availability, at two spatial scales.…”

“…At each site, we performed an epidemiological-environmental characterization. Characteristics surveyed followed a hierarchical ecological scale previously defined for the local phlebotomine species by a workshop in the frame of the IDRC Project# 107577 and already applied by Santini et al [28] and Tomhaz-Soccol et al [29]. We include in the analyses micro-and mesoscale factors that affect the presence and abundance of Phlebotominae species, in order to evaluate the environmental variables in each scenario.…”

“…Different surface buffer areas were considered at a radius of c.25, 50, 100 and 250 m. At the spatial mesoscale (buffer at a radius of > 25 m from the trap location site), environmental characteristics were evaluated using the percentages of different land cover classes and vegetation indices. Land cover classes were defined ad-hoc based on previous phlebotomine studies [28,29] and included: (i) trees or shrubs; (ii) herbaceous vegetation; (iii) crops; (iv) bare soil; (v) impervious or constructed surfaces; and (vi) water bodies. The percentages of each of the six land cover classes were estimated within circular areas centered at each sampled site.…”