Distribution of Anopheles gambiae Thioester-containing Protein 1 Alleles along Malaria Transmission Gradients in The Gambia

Thioester-containing Protein 1 (TEP1) is a highly polymorphic gene playing an important role in mosquito immunity to parasite development and associated with Anopheles gambiae sensu lato (s.l.) vectorial competence. Allelic variations in TEP1 could render mosquito either susceptible or resistant to parasite infection. Despite reports of TEP1 genetic variations in An. gambiae s.l., the correlation between TEP1 allelic variants and transmission patterns in malaria endemic settings remains unclear. Methods TEP1 allelic variants were characterised by PCR from archived genomic DNA of >1000 An. gambiae s.l. mosquitoes collected between 2009 and 2019 from eastern Gambia, where malaria transmission remains moderate but has been decreasing, and western regions with low transmission. Results Eight common TEP1 allelic variants were identi�ed at varying frequencies in An. gambiae s.l from both transmission settings. These comprised the wild type TEP1, homozygous susceptible allele, TEP1s; homozygous resistance alleles: TEP1r A and TEP1r B , and the heterozygous resistance alleles: TEP1sr A , TEP1sr B , TEP1r A r B and TEP1sr A r B . There was no signi�cant disproportionate distribution of the TEP1 alleles by transmission setting and the temporal distribution of alleles was also consistent across the transmission settings. TEP1s was the most common in all vector species in both settings (allele frequencies: East= 21.4-68.4%. West=23.5-67.2%). In An. arabiensis, the frequency of wild type TEP1 and susceptible TEP1s was signi�cantly higher in low transmission setting than in high transmission setting (TEP1: Z= -4.831, P<0.0001; TEP1s: Z= -2.073, P=0.038). The distribution of TEP1 alleles does not distinctly correlate with malaria endemicity pattern in The Gambia. Further studies are needed to understand the link between genetic variations in vector population and transmission pattern in this setting.