The impact of climate suitability, urbanisation, and connectivity on the expansion of dengue in 21st century Brazil

Dengue is hyperendemic in Brazil, with outbreaks affecting all regions. Previous studies identified geographical barriers to dengue transmission in Brazil, beyond which certain areas, such as South Brazil and the Amazon rainforest, were relatively protected from outbreaks. Recent data shows these barriers are being eroded. In this study, we explore the drivers of this expansion and identify the current limits to the dengue transmission zone. We used a spatio-temporal additive model to explore the associations between dengue outbreaks and temperature suitability, urbanisation, and connectivity to the Brazilian urban network. The model was applied to a binary outbreak indicator, assuming the official threshold value of 300 cases per 100,000 residents, for Brazil’s municipalities between 2001 and 2020. We found a nonlinear relationship between higher levels of connectivity to the Brazilian urban network and the odds of an outbreak, with lower odds in metropoles compared to regional capitals. The number of months per year with suitable temperature conditions for Aedes mosquitoes was positively associated with the dengue outbreak occurrence. Temperature suitability explained most interannual and spatial variation in South Brazil, confirming this geographical barrier is influenced by lower seasonal temperatures. Municipalities that had experienced an outbreak previously had double the odds of subsequent outbreaks. We identified geographical barriers to dengue transmission in South Brazil, western Amazon, and along the northern coast of Brazil. Although a southern barrier still exists, it has shifted south, and the Amazon no longer has a clear boundary. Few areas of Brazil remain protected from dengue outbreaks. Communities living on the edge of previous barriers are particularly susceptible to future outbreaks as they lack immunity. Control strategies should target regions at risk of future outbreaks as well as those currently within the dengue transmission zone.

The impact of climate suitability, urbanisation, and connectivity on the expansion of dengue in 21st century Brazil

Dengue is hyperendemic in Brazil, with outbreaks affecting all regions. Previous studies identified geographical barriers to dengue transmission in Brazil, beyond which certain areas, such as South Brazil and the Amazon rainforest, were relatively protected from outbreaks. Recent data shows these barriers are being eroded. In this study, we explore the drivers of this expansion and identify the current limits to the dengue transmission zone. We used a spatio-temporal additive model to explore the associations between dengue outbreaks and temperature suitability, urbanisation, and connectivity to the Brazilian urban network. The model was applied to a binary outbreak indicator, assuming the official threshold value of 300 cases per 100,000 residents, for Brazil's municipalities between 2001 and 2020. We found a nonlinear relationship between higher levels of connectivity to the Brazilian urban network and the odds of an outbreak, with lower odds in metropoles compared to regional capitals. The number of months per year with suitable temperature conditions for Aedes mosquitoes was positively associated with the dengue outbreak occurrence. Temperature suitability explained most interannual and spatial variation in South Brazil, confirming this geographical barrier is influenced by lower seasonal temperatures. Municipalities that had experienced an outbreak previously had double the odds of subsequent outbreaks, indicating that dengue tends to become established in areas after introduction. We identified geographical barriers to dengue transmission in South Brazil, western Amazon, and along the northern coast of Brazil. Although a southern barrier still exists, it has shifted south, and the Amazon no longer has a clear boundary. Few areas of Brazil remain protected from dengue outbreaks. Communities living on the edge of previous barriers are particularly susceptible to future outbreaks as they lack immunity. Control strategies should target regions at risk of future outbreaks as well as those currently within the dengue transmission zone.

Modeling the Matrix-Conduit Exchanges in Both the Epikarst and the Transmission Zone of Karst Systems

Usual conceptual models of karst hydrodynamics highlight the important role of unsaturated subsystems in recharge repartition. However, few of them have been compared with scarce suitable physically-based numerical models. Hybrid models that couple single continuum medium with discrete features promise an improved consideration of karst specificities. Here we evaluate their capability to properly reproduce interactions between a vertical conduit and the surrounding unsaturated matrix. We simulate the response of such a configuration to a single recharge event for various sets of parameters. We show the ability of hybrid models to reproduce the most significant behaviors described in the literature, i.e., transient storage and distribution of recharge, flow concentration towards conduits in the epikarst, and matrix-conduit exchanges varying in time and space. In addition to the explicit conduits, simulating variably saturated flows with the Richards equation and distinguishing the epikarst and the transmission zone are key elements to reproduce most processes. The contrasts between subsystems necessary to observe desired behaviors have been quantified. They are reinforced by the varying matrix saturation that causes realistic competition between matrix and explicit conduits. The study also highlights the need to deepen knowledge of the scaled medium properties we need to know to apply such models to actual cases.

High level of resistance in Anopheles arabiensis mosquito to pyrethroid insecticides from low malaria transmission zone of Moroto district, Karamoja region, Uganda: Implication for malaria vector control

Background: Karamoja region of Uganda previously classified as low malaria transmission zone is currently experiencing significant upsurge of malaria incidences. Long lasting insecticidal nets (LLINs) impregnated with pyrethroids constitute a major tool for malaria control in this region. Efficacy of this tool can be hampered by resistance to the pyrethroids in the Anopheles mosquito vectors. Resistance status of these mosquitoes in this region is poorly understood, effectively hampering better understanding of the impact of LLINs in the malaria control initiative. Here, we assessed susceptibility of the Anopheles arabiensis from the region to deltamethrin, permethrin (pyrethroids) and pirirmiphos-methyl (organophosphate) insecticides.Method: We collected anopheline mosquito larvae from their natural habitats and reared them to adult emergence in situ field insectary in Karamoja region. We then identified them morphological to species level and exposed 513 emerge adult female An gambiae s.l., mosquitoes to diagnostic dosages of deltamethrin (0.05%), permethrin (0.75%) and pirimiphos-methyl (0.25%) pyrethroids exposure using the standard WHO insecticide susceptibility test assay. Synergic assays using piperonyl butoxide (PBO) were done to check for the involvement of detoxification enzymes in pyrethroid resistant populations. We then screened for knockdown resistance (KDR) and mosquito species diversity using Polymerase Chain Reaction (PCR).Results: Majority (96%) of the mosquitoes we sampled were identified as An. arabiensis and 4% as An. gambiae sensu stricto. We observed cross-resistance to both deltamethrin (11.9%) and permethrin (47%) but susceptibility (100% mortality) to pirimiphos-methyl in An. arabiensis. The pre-exposure to PBO ameliorated the resistance to both pyrethroids. We detected homozygous KDR -eastern variant in 1.8 and 50% of the An. arabiensis and An. gambiae s.s. respectively.Conclusion: Anopheles arabiensis and An. gambiae s.s. are the malaria vector in Karamoja region with An. arabiensis predominating. Both species are susceptible to pirimiphos-methyl but resistant to both deltamethrin and permethrin, through a metabolic process (phenotype). Mosquotoes with genetic (kdr) mutations for resistance were minimal and hence have minimal contribution to the pyrethroid resistance profile. An. arabiensis can thus be controled in Karamoja region using deltamethrin and/or permethrin impregnated mosquito nets integrated with PBO and/or through indoor residual spraying of sprayable human dwellings with pirimiphos-methyl.

Estimating cases of severe malaria: Analysis of household surveys in 19 malaria endemic countries in Africa

Background The burden of severe malaria is uncertain at the population level because existing estimates rely heavily on data from the formal healthcare system. Using data from population-based surveys, this analysis examines severe malaria cases at the population level, which captures malaria positive children whose caregivers 1) have taken the child to a healthcare facility but the child’s illness did not resolve, or 2) have not sought care for the child’s illness. Direct inclusion of these children in severe malaria estimates has been an underlying data gap. Methods This analysis examined data from 37 Demographic and Health Surveys and Malaria Indicator Surveys across 19 countries in sub-Saharan Africa collected between 2011 and 2018. The outcome of interest is a proxy indicator for severe malaria, defined as children age 6-59 months who were positive for malaria with at least one self-reported symptom of severe illness including loss of consciousness, rapid breathing, seizures, or severe anemia (hemoglobin <5 g/dl). The study includes a weighted descriptive, country-level analysis and a multilevel mixed-effects logistic regression model to assess the determinants of severe malaria. Results Among children positive for malaria across all surveys, 4.5% (95% CI 4.1–4.8) had at least one sign or symptom of severe malaria, which was significantly associated with age, residence, wealth, and fieldwork year at a p-value less than 0.05. Malaria positive children in the higher malaria transmission zone were more likely to have signs or symptoms of severe malaria compared to those in the lowest transmission zone; however, these results were not statistically significant. Conclusion Having an accurate estimate of severe malaria cases among malaria positive children is essential to assessing the impact of malaria interventions and to guiding future malaria investments. This analysis presents a novel approach of estimating severe malaria cases among malaria positive children under age five in malaria endemic countries. Estimating severe malaria cases through household-based surveys allows countries to estimate severe malaria across time and to compare with other countries. Having a population level estimate of severe malaria cases helps further our understanding of the burden and epidemiology of severe malaria.

Estimating cases of severe malaria at the population-level: Analysis of household surveys from 19 malaria endemic countries in Africa

Background The burden of severe malaria is uncertain at the population level because existing estimates rely exclusively on data from the formal healthcare system. Using data from population-based surveys this analysis examines severe malaria cases at the population level, which captures children whose caregivers 1) have taken the child to a healthcare facility but the child’s illness did not resolve, or 2) have not sought care for the child’s illness. Direct inclusion of these children in severe malaria estimates has been an underlying data gap. Methods This analysis examined data from 37 Demographic and Health Surveys and Malaria Indicator Surveys across 19 countries in sub-Saharan Africa collected between 2011 and 2018. The outcome of interest is severe malaria, defined as children age 6–59 months who were positive for malaria with at least one self-reported symptom for severe malaria, including loss of consciousness, rapid breathing, seizures, or severe anemia. The study includes a weighted descriptive, country-level analysis and a multilevel mixed-effects logistic regression model to assess the determinants of severe malaria. Results Among children positive for malaria across all surveys, 4.5% (95% CI 4.1–4.8) had at least one symptom of severe malaria, which was significantly associated with age, residence, wealth, and survey timing at a p-value less than 0.05. Children in the higher malaria transmission zone were more likely to have symptoms compared to those in the lowest transmission zone; however, these results were not statistically significant. Conclusion An accurate estimate of the burden of severe malaria is essential to assessing the impact of malaria interventions and to guiding future malaria investments. This analysis presents a novel approach of estimating the burden of severe malaria in children under age five in malaria endemic countries. Estimating severe malaria through household-based surveys allows countries to estimate severe malaria across time and to compare with other countries. Having a population level estimate of severe malaria helps further our understanding of the burden and epidemiology of severe malaria.

Outbreak of kala azar: our experience in South Sudan

Background: Worldwide kala azar affects around 500,000 people every year with at least 50,000 deaths annually. Gedaref state in east Sudan is the epicentre of visceral leishmaniasis in east Africa. Objectives of this study were to describe the outbreak of kala azar in South Sudan, from August 2009 to July 2010, in terms of person and time distribution and to describe the outbreak of kala azar in South Sudan, from August 2009 to Jul 2010, in terms of frequency of various clinical features and outcomeMethods: A prospective cross-sectional descriptive study conducted at South Sudan with cases of kala azar affected during an outbreak in South Sudan from August 2009 to July 2010. Statistical analysis was percentage.Results: This outbreak indicates the emergence or re-emergence of kala azar in South Sudan. Within the restrictions on movement because of the civil war, further research is needed to investigate the extent of the transmission zone and whether other populations in South Sudan have been infected and have no access to treatment.Conclusions: There is lack of awareness regarding dog bite and its management among the rural population.

Sustainable provision of raw water based on the management of ecosystem services in small watersheds

The differentiated effects of the provision of environmental services in a watershed are due to the capacity of regularization of outflows in its mouth. In impacted areas, this environmental function is affected, and in some situations, it ceases to exist completely. This study characterized the soil and the production of sediments in anthropic watersheds, with the purpose of describing and evaluating the environmental services offered by a watershed undergoing anthropic transformation. The analyses show that the water flow in the remaining watersheds was preferably horizontal in the transmission zone, and these areas represent almost all areas. The values of hydraulic conductivity suggest that the infiltration decreases with soil depth; this fact is corroborated by the values of bulk density. The natural regions of water accumulation, the floodplains or outcrops zones, are small and do not have direct contact with the main floodplain present in the Guandu River Basin, making it impossible to recharge through other areas. Even so, water balance shows that the set of measures implemented ensured that the deficit water demand was supplied during the years of operation, even in times of water deficit. Likewise, the retention of solids in the settling tanks and in the drainage system prevented some 29,000 t of sediment from being carried between the years of 2012 and 2015.

High level of resistance in the mosquito Anopheles arabiensis to pyrethroid insecticides from low malaria transmission zone of Moroto district, Karamoja region, Uganda: Implication for malaria vector control

Background Karamoja region of Uganda previously classified as low malaria transmission zone is currently experiencing significant upsurge of malaria incidences. Long lasting insecticidal nets (LLINs) impregnated with pyrethroids constitute a major tool for malaria control in this region. Efficacy of this tool can be hampered by resistance to the pyrethroids in the Anopheles mosquito vectors. Resistance status of these mosquitoes in this region is poorly understood, effectively hampering better understanding of the impact of LLINs in the malaria control initiative. Here, we assessed susceptibility of the Anopheles arabiensis from the region to deltamethrin, permethrin (pyrethroids) and pirirmiphos-methyl (organophosphate) insecticides. Method We collected anopheline mosquito larvae from their natural habitats and reared them to adult emergence in situ field insectary in Karamoja region. We then identified them morphological to species level and exposed 513 emerge adult female An gambiae s.l., mosquitoes to diagnostic dosages of deltamethrin (0.05%), permethrin (0.75%) and pirimiphos-methyl (0.25%) pyrethroids exposure using the standard WHO insecticide susceptibility test assay. Synergic assays using piperonyl butoxide (PBO) were done to check for the involvement of detoxification enzymes in pyrethroid resistant populations. We then screened for knockdown resistance (KDR) and mosquito species diversity using Polymerase Chain Reaction (PCR). Results Majority (96%) of the mosquitoes we sampled were identified as An. arabiensis and 4% as An. gambiae sensu stricto . We observed cross-resistance to both deltamethrin (11.9%) and permethrin (47%) but susceptibility (100% mortality) to pirimiphos-methyl in An. arabiensis . The pre-exposure to PBO ameliorated the resistance to both pyrethroids. We detected homozygous KDR -eastern variant in 1.8 and 50% of the An. arabiensis and An. gambiae s.s. respectively. Conclusion Anopheles arabiensis and An. gambiae s.s. are the malaria vector in Karamoja region with An. arabiensis predominating. Both species are susceptible to pirimiphos-methyl but resistant to both deltamethrin and permethrin, through a metabolic process (phenotype). Mosquotoes with genetic (kdr) mutations for resistance were minimal and hence have minimal contribution to the pyrethroid resistance profile. An. arabiensis can thus be controled in Karamoja region using deltamethrin and/or permethrin impregnated mosquito nets integrated with PBO and/or through indoor residual spraying of sprayable human dwellings with pirimiphos-methyl.