Automatic Detection of Open and Vegetated Water Bodies Using Sentinel 1 to Map African Malaria Vector Mosquito Breeding Habitats

Providing timely and accurate maps of surface water is valuable for mapping malaria risk and targeting disease control interventions. Radar satellite remote sensing has the potential to provide this information but current approaches are not suitable for mapping African malarial mosquito aquatic habitats that tend to be highly dynamic, often with emergent vegetation. We present a novel approach for mapping both open and vegetated water bodies using serial Sentinel-1 imagery for Western Zambia. This region is dominated by the seasonally inundated Upper Zambezi floodplain that suffers from a number of public health challenges. The approach uses open source segmentation and machine learning (extra trees classifier), applied to training data that are automatically derived using freely available ancillary data. Refinement is implemented through a consensus approach and Otsu thresholding to eliminate false positives due to dry flat sandy areas. The results indicate a high degree of accuracy (mean overall accuracy 92% st dev 3.6) providing a tractable solution for operationally mapping water bodies in similar large river floodplain unforested environments. For the period studied, 70% of the total water extent mapped was attributed to vegetated water, highlighting the importance of mapping both open and vegetated water bodies for surface water mapping

Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

Background The Barotse floodplains of the upper Zambezi River and its tributaries are a highly dynamic environment, with seasonal flooding and transhumance presenting a shifting mosaic of potential larval habitat and human and livestock bloodmeals for malaria vector mosquitoes. However, limited entomological surveillance has been undertaken to characterise the vector community in these floodplains and their environs. Such information is necessary as, despite substantial deployment of insecticide-treated nets (ITNs) and indoor residual spraying (IRS) against Anopheles vectors, malaria transmission persists across Barotseland in Zambia’s Western Province. Methods Geographically extensive larval surveys were undertaken in two health districts along 102 km of transects, at fine spatial resolution, during a dry season and following the peak of the successive wet season. Larvae were sampled within typical Anopheles flight range of human settlements and identified through genetic sequencing of cytochrome c oxidase I and internal transcribed spacer 2 regions of mitochondrial and nuclear DNA. This facilitated detailed comparison of taxon-specific abundance patterns between ecological zones differentiated by hydrological controls. Results An unexpected paucity of primary vectors was revealed, with An. gambiae s.l. and An. funestus representing <2% of 995 sequenced anophelines. Potential secondary vectors predominated in the vector community, primarily An. coustani group species and An squamosus. Whilst the distribution of An. gambiae s.l. in the study area was highly clustered, secondary vector species were ubiquitous across the landscape in both dry and wet seasons, with some taxon-specific relationships between abundance and ecological zones by season. Conclusions The diversity of candidate vector species and their high relative abundance observed across diverse hydro-ecosystems indicates a highly adaptable transmission system, resilient to environmental variation and, potentially, interventions that target only part of the vector community. Larval survey results imply that residual transmission of malaria in Barotseland is being mediated predominantly by secondary vector species, whose known tendencies for crepuscular and outdoor biting renders them largely insensitive to prevalent vector control methods

Maintaining HIV testing and treatment services in Zambia during COVID-19: a story of success and resilience

Background Coronavirus disease 2019 (COVID-19) is caused by a virus called severe acute respiratory syndrome coronavirus. As countries struggled to control the spread of the virus through among other measures closure of health facilities, repurposing of health care workers, and restrictions on people’s movement, HIV service delivery was affected. Objectives To assess the impact of COVID-19 on HIV service delivery in Zambia by comparing uptake of HIV services before and during COVID-19. Methods We used repeated cross-sectional quarterly and monthly data on HIV testing, HIV positivity rate, people living with HIV initiating ART and use of essential hospital services from July 2018 to December 2020. We assessed quarterly trends and measured proportionate changes comparing periods before and during COVID-19 divided into three different comparison time frames: (1) annual comparison 2019 versus 2020; (2) April to December 2019 versus same period in 2020; and (3) Quarter 1 of 2020 as base period versus each of the other quarters of year 2020. Results Annual HIV testing dropped by 43.7% (95%CI 43.6–43.7) in 2020 compared to 2019 and was similar by sex. Overall, annual recorded number of newly diagnosed PLHIV fell by 26.5% (95% CI 26.37–26.73) in 2020 compared to 2019, but HIV positivity rate was higher in 2020, 6.44% (95%CI 6.41–6.47) compared to 4.94% (95% CI 4.92–4.96) in 2019. Annual ART initiation dropped by 19.9% (95%CI 19.7–20.0) in 2020 compared to 2019 while use of essential hospital services dropped during the early months of COVID-19 April to August 2020 but picked up later in the year. Conclusion While COVID-19 had a negative impact on health service delivery, its impact on HIV service delivery was not huge. HIV policies that were implemented before COVID-19 on testing made it easier to adopt COVID-19 control measures and to continue providing HIV testing services without much disruption