Evaluating the determinants of the spread of COVID-19 between and within rural communities in Mali, West Africa based on blood-fed mosquitoes

National Institute Of Allergy And Infectious Diseases

Investigators

Abstract

The spread of COVID-19 in rural sub-Saharan Africa is poorly understood and reliable data are unlikely to be obtained as a result of low capacity for disease surveillance. Additionally, these areas have 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 500km. Immunoglobulin-G antibodies were found to be readily detectable within the mosquito bloodmeals by a bead-based immunoassay through 10 (and up to 20) hours post-feeding, indicating that most mosquitoes collected via indoor aspiration catches (that likely fed the previous night and are now resting), are viable samples for analysis. These results were obtained with desiccated mosquitoes (over silica gel). Notably, blood fed mosquitoes preserved in 80% ethanol exhibited rapid degradation of the antibodies, resulting in poor detection. Accordingly, we have amended our SOP and preserve all mosquitoes by desiccation over silica gel. By May 2021, a total of 9,519 blood-fed mosquitoes were collected from the villages on silicagel (mean 68/village/month). Since collection covered the dry season mostly, we anticipate a larger number to be collected in the coming months. Experiments to test detection of antibodies to two spike domains, RBD, and nucleocapsid of COVID-19 using a bead-based immunoassay over time after blood feeding showed high detection capacity of all antibodies up to 10 and often 20 hours post blood feeding. Essentially identical results for antibody persistence in bloodmeals were produced using ELISA on the spike and RBD proteins in our lab in Mali. Since we collect mosquitoes that blood fed 4-10 hours earlier, the vast majority of the mosquito blood-meals are suitable for serological assay. Among our focal 20 villages, 3 are the same sites where collaborators have carried out serological tests on residents in August/September 2020 and in January/February 2021 (Sagara et al. 2021). To evaluate our methodology, we have started testing mosquito samples from these communities at these time points. Crude seropositivity of blood sampled via mosquitoes was 1.96% in October/November 2020 across all sites, and increased to 16.4% overall at the site closest to Bamako reaching 33.3% in February of 2021. These trends are similar but suggest lower prevalence that reported by the Sagara et al. 2021. A paper summarizing the results of 5 villages at these time points is being written while serological data are being added.