Relationship between the colors of the rivers in the Amazon and the incidence of malaria

Background Malaria is an infection caused by parasites of the genus Plasmodium, which are transmitted to humans via the bite of the female Anopheles mosquito. In Brazil, approximately 99% of malaria cases are concentrated in the Amazon region. Os rios desempenham um papel importante no ciclo de vida da malária, uma vez que o vetor se reproduz em ambiente aquático. The waters of the rivers in the Amazon have distinct chemical characteristics and this prompted us to analyze the influence of the color of the waters of the rivers in the Amazon on the distribution of malaria. Methodology This study was conducted for a period of seventeen years (2003-2019) in 50 municipalities in the state of Amazonas, Brazil. A generalized linear mixed model was developed to analyze the association of malaria incidence and three types of river color: white, black and mixed. Principal Findings The results suggest that there is a trend towards a decrease in malaria cases until 2015, with a possible resumption of the incidence of the disease from 2017 onwards, in all types of river color. In addition, the research indicates that places located near black-or mixed-water rivers have a higher incidence of malaria when compared to places on the banks of white-water rivers. Conclusions Historically, the hydrological regime has played an important role in the dynamics of malaria in the Amazon, but little is known about the relationship between river colors and the incidence of the disease. In this sense, our results, by showing a significant association between the colors of the rivers and the incidence of malaria over time, seem to expand the understanding between physical-chemical characteristics of the rivers and the occurrence of malaria. Author summary Malaria is a disease that has a major impact on morbidity in tropical and subtropical countries. In Brazil, most of the cases registered in the country are concentrated in the northern region. A variety of factors can contribute to the occurrence of malaria outbreaks or epidemics, and rivers play an important role in the transmission of the disease. The waters of the rivers in the Amazon have distinct chemical characteristics and this study sought to analyze the influence of the color of the waters of the rivers in the Amazon on the distribution of malaria. Data on the incidence of malaria, from 2003 to 2019, in 50 municipalities in the state of Amazonas, Brazil, were associated with three types of river coloration: white, black and mixed. The results demonstrated the existence of a trend towards a decrease in malaria over the years, in all types of river coloration, and that this trend does not seem to be associated with the different types of water. However, the research indicates that places located near black-or mixed-water rivers have a higher incidence of malaria, when compared to places on the banks of white-water rivers.