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Principal Investigator: Tovi Lehmann
Organization: NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES
Fiscal Year: 2024
Award: $731,182
Funding agency: National Institute of Allergy and Infectious Diseases
The spread of COVID-19 in rural sub-Saharan Africa is poorly understood and reliable data are unlikely to be obtained because of low capacity for disease surveillance, compounded by high proportion of young population that present mostly asymptomatic or low-symptomatic infections. To fill this gap and assess how the unique ecological and cultural settings affect it, we have initiated a novel epidemiological study, monitoring COVID-19 infections by sampling blood-fed mosquitoes collected monthly in houses of 20 Malian villages spread across ~500 km. From October 2020 to May 2022, a total of 48,805 female mosquitoes were collected in over 27,900 house visits. Experiments using these and laboratory mosquitoes were carried out in Mali and in NIH to provide a proof of concept to the feasibility of this project as a prerequisite before expansion to the full scope of this work.
Immunoglobulin-G antibodies were readily detectable within the mosquito bloodmeals by a bead-based immunoassay through 10 hours post-feeding, indicating that most mosquitoes collected indoors (that likely fed the previous night and are now resting), are viable samples for analysis. Using pre-pandemic blood-fed mosquitoes we established antigen specific cutoffs (mean 5*STD) to identify mosquitoes that fed on Covid-seropositive and seronegative humans for antibodies against the i) nucleocapsid, ii) the receptor binding domain (RBD), and iii-iv) the two spike domains. By requiring at least 2 antibody titers to exceed their cutoffs the sensitivity was 0.90 and specificity was 0.92. Using this assay, we evaluated the change in sero-prevalence of one urban and four rural communities in Mali. Consistent with a conventional serological study in Mali (Sagara et al. 2021), crude sero-positivity of blood sampled via mosquitoes was 6.3% in October/November 2020 over all sites, and increased to 25.1% overall, with the town closest to Bamako (Sotuba) reaching 46.7% in February of 2021. Adjusted to mosquitoes feeding on non-human hosts and to the possibility of multiple mosquitoes feeding on the same individual human changed the results little because most mosquitoes fed on human blood and relatively small number of mosquitoes were analyzed from each house at a period. In finding this a viable technique amenable to conventional immunoassays to measure population-level sero-prevalance, we feel sero-surveillance of human diseases, regardless if they are vector-borne, is attainable, non-invasive sampling option, especially suited to areas with high density of human-biting mosquitoes. Our first paper (Krajacich et al. 2023) summarizing the results of 5 villages at two time points has been published in Frontiers in Epidemiology.
Additionally, our team in Mali has been performing ELISA assays to detect antibodies against the Spike and RBD based on protocols optimized by the LMIV (Woodford et al. 2021). Over 8,000 mosquitoes were assayed for both antigens. The assortment of villages used in this study was different from the subset used in the four-antigen bead assay (above). We plan to analyze these data representing multiple time points from October 2020 to September 2022 from 20 rural communities, which will provide the dynamics of spread of COVID-19 in Mali during the first years of the pandemic.
Finally, we have trained a group from Burkina Faso to carry out the same surveillance approach in Burkina Faso focusing on the field and laboratory methods. Currently we assist in writing the results this collaboration has yielded (de Souza et al.: Seroprevalence of SARS-CoV-2 in Rural Communities of Burkina Faso (West Africa) assessed through blood-fed Mosquitoes. In Prep).
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