A piece of the puzzle: seasonality, distribution and Leishmania infection rates in sand flies on the Brazilian side of Foz do Iguaçu

Abstract

Background: The recent geographic expansion of Leishmania infantum vectors in the triple border area of Argentina, Brazil, and Paraguay has highlighted the need to know the seasonality, parasite infection rate, and the factors that contribute the dispersal and handling of this parasite. Methods: Entomological, quantitative longitudinal studies were conducted in Foz do Iguaçu, Brazil, where sand fly abundance was higher in cross-sectional studies. Monthly sand fly samplings occurred in 2014-2015. LeishmaniaDNA was detected by PCR and subsequently sequenced, classified, and the infection rate was estimated. The study also featured an observational and descriptive design. Environmental variables were analyzed at the micro- and mesoscales, and the data were evaluated along with entomological and infection inputs. Results: A total of 3,582 sand flies were caught. Lutzomyia longipalpiswas the predominant species (71.5%) among 13 species found in one year of sampling. Four species, Evandromyia edwardsi, Expapillata firmatoi, Micropygomyia ferreirana, and Pintomyia christenseni were reported for the first time. The NDVI, distance from water, sex, west-to-east wind, and wind speed were significant variables for the intra-environment presence and/or abundance of vectors. The presence and/or abundance of vectors in peri-domicile were influenced by rain, altitude, maximum temperature, minimum and maximum relative humidity, west-to-east wind, wind speed, and sex. Considering PCR positivity, females infected with L. infantum were found throughout the year, and especially with Lu. longipalpis (prevalence means of 16.4). Conclusions: Vector colonization concentrates on urban and peri-urban hotspot areas, with some individuals being present in various parts of the city and few sites showing high vector abundance. This distribution suggests that the risk of actual contact between humans and parasitic vectors in urban areas during the epidemic period is associated with patches of peri-urban vegetation and then spreads across urban areas. We can state that, in the period of this study, the most critical transmission phase for L. infantum in the region is from January to May. Therefore, future management plants to reduce access to reservoirs might reduce sand fly infection and consequently human and animal infections.