Unravelling Anopheles Dynamics in a Malaria-Free Paraguay: Species Distributions, Bioclimatic Niches, and Implications for Resurgence Risks

Malaria, caused by a protozoan parasite of the genus <i>Plasmodium</i> and transmitted by mosquitoes of the genus <i>Anopheles</i>, remains a significant vector-borne disease worldwide. In 2018, Paraguay became the first country in the Americas in 45 years to be certified malaria-free by the World Health Organization. Between 2016 and 2017, a period with no reported human malaria cases, the presence of <i>Plasmodium</i> spp. in <i>Anopheles</i> mosquitoes was investigated in the departments of Caaguazú and Alto Paraná. These studies found that the most prevalent <i>Anopheles</i> species in Paraguay, including <i>Anopheles albitarsis</i> (59.4%), <i>Anopheles strodei</i> (21.5%), and other <i>Anopheles</i> species in smaller proportions, were all negative to the parasite. The objective of this study was to re-evaluate these presence data and to define environmentally suitable areas for <i>Anopheles</i> spp. and their association with bioclimatic variables using DIVA-GIS/MaxEnt software for the entomological surveillance of malaria risk in Paraguay. Results showed that areas of bioclimatic suitability included the Humid Chaco, Cerrado, Paraná Atlantic Forest, and Southern Cone Mesopotamian savanna ecoregions. The most relevant climatic variables were the precipitation of the wettest month (contribution of 80.4%) and the precipitation of the driest month (contribution of 18.4%). <i>Anopheles albitarsis</i>, also reported as a vector of the Venezuelan equine encephalitis virus in neighbouring countries, was the most abundant mosquito species. <i>Anopheles darlingi</i>, the main vector of malaria in Paraguay, was not found. However, species richness indices (Chao/ACE) suggest that cryptic or sibling species may be present. Finally, the possible succession of <i>Anopheles</i> species and their geographical segregation are discussed in scenarios of entomological surveillance and epidemiological risk.