Cohort profile: the Mâncio Lima cohort study of urban malaria in Amazonian Brazil

PurposeThis population-based open cohort study aims to investigate biological and sociodemographic drivers of malaria transmission in the main urban hotspot of Amazonian Brazil.ParticipantsNearly 20% of the households in the northwestern town of Mâncio Lima were randomly selected and 2690 participants were enrolled since April 2018. Sociodemographic, housing quality, occupational, behavioural and morbidity information and travel histories were collected during consecutive study visits. Blood samples from participants>3 months old were used for malaria diagnosis and human genetic studies; samples from participants with laboratory-confirmed malaria have been cryopreserved for genetic and phenotypic characterisation of parasites. Serology was introduced in 2020 to measure the prevalence and longevity of SARS-CoV-2 IgG antibodies.Findings to dateMalaria prevalence rates were low (up to 1.0% for Plasmodium vivax and 0.6% for P. falciparum) during five consecutive cross-sectional surveys between April–May 2018 and October–November 2020; 63% of infections diagnosed by microscopy were asymptomatic. Malaria risk is heterogeneously distributed, with 20% study participants contributing 86% of the overall burden of P. vivax infection. Adult males are at greatest risk of infection and human mobility across the urban–rural interface may contribute to sustained malaria transmission. Local P. vivax parasites are genetically diverse and fragmented into discrete inbred lineages that remain stable across space and time.Future plansTwo follow-up visits, with similar study protocols, are planned in 2021. We aim to identify high-risk individuals that fuel onwards malaria transmission and represent a priority target for more intensive and effective control interventions.Trial registration numberNCT03689036.

Susceptibility of Field-Collected Nyssorhynchus darlingi to Plasmodium spp. in Western Amazonian Brazil

Mosquito susceptibility to Plasmodium spp. infection is of paramount importance for malaria occurrence and sustainable transmission. Therefore, understanding the genetic features underlying the mechanisms of susceptibility traits is pivotal to assessing malaria transmission dynamics in endemic areas. The aim of this study was to investigate the susceptibility of Nyssorhynchus darlingi—the dominant malaria vector in Brazil—to Plasmodium spp. using a reduced representation genome-sequencing protocol. The investigation was performed using a genome-wide association study (GWAS) to identify mosquito genes that are predicted to modulate the susceptibility of natural populations of the mosquito to Plasmodium infection. After applying the sequence alignment protocol, we generated the variant panel and filtered variants; leading to the detection of 202,837 SNPs in all specimens analyzed. The resulting panel was used to perform GWAS by comparing the pool of SNP variants present in Ny. darlingi infected with Plasmodium spp. with the pool obtained in field-collected mosquitoes with no evidence of infection by the parasite (all mosquitoes were tested separately using RT-PCR). The GWAS results for infection status showed two statistically significant variants adjacent to important genes that can be associated with susceptibility to Plasmodium infection: Cytochrome P450 (cyp450) and chitinase. This study provides relevant knowledge on malaria transmission dynamics by using a genomic approach to identify mosquito genes associated with susceptibility to Plasmodium infection in Ny. darlingi in western Amazonian Brazil.

Low-level Plasmodium vivax exposure, maternal antibodies, and anemia in early childhood: Population-based birth cohort study in Amazonian Brazil

Background Malaria causes significant morbidity and mortality in children under 5 years of age in sub-Saharan Africa and the Asia-Pacific region. Neonates and young infants remain relatively protected from clinical disease and the transplacental transfer of maternal antibodies is hypothesized as one of the protective factors. The adverse health effects of Plasmodium vivax malaria in early childhood–traditionally viewed as a benign infection–remain largely neglected in relatively low-endemicity settings across the Amazon. Methodology/Principal findings Overall, 1,539 children participating in a birth cohort study in the main transmission hotspot of Amazonian Brazil had a questionnaire administered, and blood sampled at the two-year follow-up visit. Only 7.1% of them experienced malaria confirmed by microscopy during their first 2 years of life– 89.1% of the infections were caused by P. vivax. Young infants appear to be little exposed to, or largely protected from infection, but children >12 months of age become as vulnerable to vivax malaria as their mothers. Few (1.4%) children experienced ≥4 infections during the 2-year follow-up, accounting for 43.4% of the overall malaria burden among study participants. Antenatal malaria diagnosed by microscopy during pregnancy or by PCR at delivery emerged as a significant correlate of subsequent risk of P. vivax infection in the offspring (incidence rate ratio, 2.58; P = 0.002), after adjusting for local transmission intensity. Anti-P. vivax antibodies measured at delivery do not protect mothers from subsequent malaria; whether maternal antibodies transferred to the fetus reduce early malaria risk in children remains undetermined. Finally, recent and repeated vivax malaria episodes in early childhood are associated with increased risk of anemia at the age of 2 years in this relatively low-endemicity setting. Conclusions/Significance Antenatal infection increases the risk of vivax malaria in the offspring and repeated childhood P. vivax infections are associated with anemia at the age of 2 years.

Morphological, Cytochemical and Ultrastructural Aspects of Blood Cells in Freshwater Stingray Species in the Middle Rio Negro Basin, Amazonian, Brazil

Examined the morphology, dimensions, cytochemical staining reactions and ultrastructure of blood cells from three freshwater stingray species, Potamotrygon wallacei, Potamotrygon motoro and Paratrygon aiereba, living in the waters of the middle Rio Negro basin (Barcelos, Amazonas, Brazil). We identified erythrocytes, erythroblasts, thrombocytes and four types of leukocyte (basophils, heterophils, lymphocytes and monocytes) in the blood of these stingray species. In all the freshwater stingrays studied, the shape and dimensions of these cells were similar to those of marine elasmobranchs. A positive PAS reaction occurred in heterophils and thrombocytes, and a weak reaction in lymphocytes and monocytes, while a metachromasia reaction only occurred in basophils. Sudan black staining was positive for thrombocytes and lymphocytes, and only a weak reaction occurred in heterophils. Basophils and heterophils were the only cells stained with bromophenol blue, while no peroxidase reaction was observed in any leukocyte type. This is the first study to establish the dimensions and cytochemical staining reactions of blood cells in Amazonian stingray species. Since these elasmobranch species are exported as ornamental fish to countries worldwide, this study can contribute towards establishing standards for blood constituents that may be helpful in assessing the health and welfare of these fish in artificial systems.

A statistical-based reach scale classification for the lower Tapajós river channel, eastern Amazonia

The Tapajós river is among the largest rivers in the world and has been credited as the main affluent of the lower Amazon River. Geomorphological studies in the Tapajós commonly deal with evolutionary, hydrological, and sedimentological issues. Recently, important advances have been made in understanding the morphology and dynamics in the Tapajós, especially in the confluence zone near Santarém, eastern Amazonian Brazil. However, the lack of an independent channel classification system makes it difficult to integrate data obtained from different sources. This work presents a classification system for the lower Tapajós based on morphometric variables extracted from transversal profiles coupled with radar and optical remote sensing data. We used discriminant analysis of principal components for the first time in fluvial geomorphology to provide a clustering-based geomorphological classification, which is statistically supported. We propose a segmentation of the channel into three distinct sections referred to as narrower channel reach, higher ria reach, and lower ria reach. The results showed that the channel has a distinct morphological pattern in each of these reaches, which can also be observed by the variation along the longitudinal profile. Our findings showed that the most variable hydrological and sedimentological patterns are found in the lower ria reach, while the higher ria reach comprises a canyon-shaped, more stable part of the channel. We discuss the implications of this pattern on the ria’s evolution. The method developed here could be applied to other areas of the Amazon basin, where the lack of data and logistical difficulties carrying out fieldwork are common obstacles to large-scale investigations. The identified reaches are indended to be considered in the sample design of future works and in the formulation of water resources management strategies.

Coleoborers (Curculionidae: Scolytinae) in native and homogeneous systems of Brazil nut (Bertholletia excelsa bonpl.) in the Southern Amazon, Brazil

Brazil nut is one of the most important species of the Amazon due to its socioeconomic importance. Especially in homogeneous production systems, it may be susceptible to damage by wood-boring insects, as by the subfamily Scolytinae (Coleoptera: Curculionidae); thus, inadequate management conditions can cause economic damage. Therefore, the objective of the present work is to evaluate the occurrence of wood-boring insects (Curculionidae: Scolytinae) in native and homogeneous systems of Brazil nut in the Meridional Amazonian, Brazil. The study was conducted in three environments: Brazil Nut Native Anthropized, Homogeneous Brazil Nut and Brazil Nut Native Preserved. Twelve ethanol (96° GL) traps were installed in each environment during four sampling periods. The data were submitted to entomofaunistic analysis, Pearson´s correlation analysis and cluster analysis. A total of 2,243 individuals from 31 species were sampled, of which 23 were from the Brazil Nut Native Anthropized nut, 24 from the Homogeneous Brazil Nut and 26 from the Brazil Nut Native Preserved. Some species are restricted to a specific environment, such as Corthylocurus vernaculus Wood & Bright, 1992 and Xyleborus biconicus Eggers, 1928, in relation to Brazil Nut Native Anthropized, Xyleborus tolimanus Eggers, 1928 that occurred only in Homogeneous Brazil Nut and Corthylus antennarius Schedl and Hypothenus bolivianus Wood & Bright, 1992 verified only in Brazil Nut Native Preserved. In the faunistic analysis, we highlight the species Xyleborus affinis (Eichhoff, 1868), which was the most representative one in the three environments and a super-dominant species in all four sampling periods. Among the species considered indicator due to their high representativeness in the sampling, only Premnobius cavipennis Eichhoff, 1878 showed a significant negative correlation between its abundance and the minimum temperature for environments Homogeneous Brazil Nut and Brazil Nut Native Preserved. There was a greater similarity between the Brazil Nut Native Anthropized and the Brazil Nut Native Preserved; these two environments showed dissimilarity with the Homogeneous Brazil Nut. Monitoring wood-boring insects in Brazil nut agroecosystems is fundamental for the establishment of integrated pest management strategies.

Fish fauna of small-order streams of savannah and forest fragments landscape in the lower Tapajós River basin, Amazonia

To better understand the fish fauna of Amazonian streams, we assessed small streams in a landscape of forest fragments and savannah in the region of the lower Tapajós River, Brazil. We sampled the fish fauna using a well-tested active capture method during two dry seasons (October 2006 and 2018) and one rainy season (March to May 2018). Species richness was calculated using an abundance matrix and first-order jackknife estimator. Using qualitative and quantitative data, we present a cluster analysis in which each stream corresponds to a sampling unit. We collected 6,094 individuals of 43 species distributed in six orders. The sampling effort represents 73% of the estimated richness (58.69 ± 7.65). The most abundant species were Copella nattereri, Iguanodectes variatus and Laimosemion dibaphus that together represent almost half of the total sample (48.7%). The most frequent species were Aequidens epae, Helogenes marmoratus and Laimosemion dibaphus, which were collected in 11 of the 13 sampled streams. This is the first fish fauna list for small-order streams of savannah and forest fragments landscape in Amazonian Brazil. The richness of fish and the presence of many rare species underscore the contribution of small streams to the regional fish fauna composition, even in dynamic and spatially restricted landscapes.

Updating the checklist of subtribe Hyptidinae (Lamiaceae) from Brazilian Amazonia, with three new taxa and notes on Hyptis sect. Eriosphaeria

Three new taxa of subtribe Hyptidinae (Lamiaceae) from Amazonian Brazil are here described: two from Pará state Eriope macrostachya var. amazonica, and Hyptis cachimboensis, and Hyptis spathulata from Rondônia state. The diagnostic characters, which distinguish them from their closest relatives are described and discussed, their conservation status is given and a plate is provided for each of the new taxa. The Hyptidinae conspectus an earlier checklist of Lamiaceae from Amazonian Brazil is updated with various name changes since its publication, and with the addition of another two species of Hyptis not previously included. Also included, is a note on Hyptis sect. Eriosphaeria, to which the two new species described here, belong.

Human mobility and urban malaria risk in the main transmission hotspot of Amazonian Brazil

Malaria in the Amazon is often perceived as an exclusively rural disease, but transmission has been increasingly documented within and near urban centers. Here we explore patterns and causes of urban-to-rural mobility, which places travelers at risk of malaria in Mâncio Lima, the main malaria hotspot in northwestern Brazil. We also analyze rural-to-urban mobility caused by malaria treatment seeking, which poses an additional risk of infection to urban residents. We show that the rural localities most frequently visited by urban residents–typically farming settlements in the vicinity of the town–are those with the most intense malaria transmission and also the most frequent source localities of imported malaria cases diagnosed in the town. The most mobile urban residents are typically poor males 16 to 60-years old from multi-sited households who lack a formal job. Highly mobile residents represent a priority target for more intensive and effective malaria control interventions, that cannot be readily delivered to the entire community, in this and similar urbanized endemic settings across the Amazon.