Genotyping of Anopheles mosquito blood meals reveals nonrandom human host selection: implications for Plasmodium falciparum transmission, Malawi

Genotyping of human blood in arthropod vector blood meals, allows identification of individual humans who were fed upon. This approach has improved understanding of parasite transmission in several vector-borne disease systems, including malaria. We used microsatellite-based genotyping to identify which humans were naturally transmitting Plasmodium falciparum to Anopheles vector mosquitoes. The study was conducted in two districts of moderate-to-high malaria transmission in southeastern Malawi. Household surveys were conducted (n=46) to ascertain human demographic information. Blood spots were obtained on filter paper by fingerprick from consented participants. Indoor resting, blood-fed, female Anopheles mosquitoes were repeatedly sampled from inside participants’ houses every two weeks during peak transmission (April 2020) by pyrethroid spray catches and CDC light traps. Genomic DNA from human blood spots and mosquito blood meals was genotyped and unique profiles identified and matched using a program in RStudio. Polymerase Chain Reactions (PCR) were used to detect P. falciparum DNA in human and mosquito samples. Human blood was detected in 370 mosquito samples, of which 12% (n=44) contained more than one human genotype. Few individuals contributed most of the blood meals to the Anopheles vector population. 46 unique human genotypes from the at-risk human participants (n=250) were found among the 370 mosquito blood meals. The number of blood meals taken from individual people ranged from 1 to 51. More blood meals (60%) came from males than females even though fewer males (38%) participated in the study. Among blood meals that matched genotyped participants, vectors fed more frequently on school-age children (SAC) (6-15 years old) than younger children and adults. Mosquitoes that had fed upon male SAC had the highest P. falciparum infection prevalence in their abdomens. Results support the hypothesis that SAC, particularly males, are important reservoirs of P. falciparum transmission from humans to mosquitoes. Thus, interventions aimed at reducing P. falciparum transmission should preferentially target this population.