Balieiro, A. | bioRxiv Science

bioRxiv2023

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

BackgroundMalaria 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 malaria, uma vez que o vetor se reproduz em ambiente aquatico. 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. MethodologyThis 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 FindingsThe 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. ConclusionsHistorically, 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 summaryMalaria 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.

ecology↗

bioRxiv2018

Natural avirulent Shigella boydii strain in the Brazilian Amazon lacks major virulence genes and present Type II, Type III and Type VI Secretion Systems

BackgroundAmong Shigella species, Shigella boydii has always displayed a smaller role to the overall Shigella burden, frequently placed at third in epidemiological studies and described as restricted to Southeast Asia. Here we characterize an S. boydii isolated from an epidemiological study enrolling 1,339 Brazilian children from the Amazon region, in which Shigella species solely was the fourth cause of bacterial diarrhea. S. boydii strain 183 was isolated from rotavirus co-infected children with acute diarrhea. Here we aimed to characterize this strain regarding virulence and, immune response in a pulmonary model.\n\nMethodsAn in vitro HEp-2 epithelial cell invasion assay was used to compare the invasive phenotype of S. boydii strain 183 with clinical and highly virulent S. flexneri strain, both isolated from Brazilian children. A murine pulmonary model was performed to assess lung damage by histopathological analysis. mRNA expression of immune response key genes was retrieved by multiplex real-time PCR and correlations were obtained by network analysis. Broad genome analysis was performed to confirm S. boydii identity and define its virulence profile.\n\nResultsS. boydii strain 183 showed fewer invasion rates in vitro and tissue damage in vivo as compared to virulent S. flexneri 201. When compared to a survival challenge in mice, S. boydii had 100% survival against 10% of virulent S. flexneri. Overall, mRNA immune gene expression suggests a protective response against S. boydii strains 183, in contrast to the inflammatory response induced by the virulent S. flexneri strain 201. Network analysis with S. boydii strain 183 displayed IFN-{gamma} protagonism, contrasting with the correlations centralized on TNF- by the virulent S. flexneri strain 201. The genome showed a lack of effector proteins and enterotoxins in S. boydii strain 183, and sequencing analysis of Ipa invasins revealed mutations at functional sites. This avirulent S. boydii strain 183 presents the Type II Secretion System, T6SS, in addition to T3SS.\n\nConclusionsIn addition to causing no disease, S. boydii strain 183 lacks effector proteins and enterotoxins. The presence of T6SS additional secretion system could provide an advantage to establish this strain among commensal bacteria.\n\nAUTHOR SUMMARYThe Shigella genus is a human pathogen responsible to shigellosis and remains one of the significant causes of morbidity and mortality in children under five years old. This genus has four species, Shigella flexneri, Shigella sonnei, Shigella boydii, and Shigella dysenteriae. S. flexneri and S. sonnei are the most common in the worldwide infections; S. dysenteriae is rarely found, and S. boydii is responsible for 1% of the infections and is known to be restricted to Southeast Asia. Once S. boydii have a relatively small role in global Shigella disease, there are few studies regarding its virulence and mechanisms. Here we characterize an S. boydii isolated from Brazilian children from the Amazon region, and aimed to describe this strain regarding virulence. It is known that Shigella species use the Type 3 Secretion System (T3SS) to invade and colonize the human intestine. We found in S. boydii the presence of Type 2 Secretion System (T2SS), Type 6 Secretion System (T6SS), in addition to the T3SS. The T6SS have been described in S. sonnei only, granting a competitive advantage against S. flexneri mixed cultures. The presence of T6SS additional secretion system could provide a benefit to establish this strain among commensal bacteria.

microbiology↗