Genetic variants, seasonal abundance and man-biting rate of Anopheles gambiae sensulato in Bali, Taraba State, Nigeria

Abstract

Anopheles gambiae sensu lato, the largely anthropophilic and endophylic complex species is reportedly the most important malaria vector in tropical Africa, including Nigeria. Indoor mosquitoes were caught monthly in Bali area by pyrethrum-Spray catch (PSC) from September 2015 to August 2016. Morphologically identified Anopheles gambiae s.l. species were amplified by PCR to characterize sibling species using species specific single nucleotide polymorphism (SNPs) with primers specific for An. gambiae s.s., An. arabiensis, An. melas, and An. quadriannulatus. Molecular forms of the An. gambiae s.s were further identified by PCR-Restriction Fragment Length Polymorphism assay using primers specific for Mopti (M) and Savannah (S) forms. Out of a total of 188 samples 99.5% (n = 187) were all identified as Anopheles gambiae sensu stricto and spread across the study months. Anopheles arabiensis 1 (0.5%) was found in Bali. Out of 187 An. gambiae s.s. samples analysed 154 (82.4%) were identified as Anopheles coluzzii (formerly Mopti (M) form), 24 (12.8%) were identified as Anopheles gambiae s.s. Giles or Anopheles gambiae (formerly Savannah (S) form) and 9 (4.8%) were identified as Anopheles coluzzii/Anopheles gambiae hybrid (M/S form). Anopheles gambiae (Molecular S form), Anopheles gambiae (Molecular Mform) and the hybrids occurred in sympatry with variations in monthly/seasonal abundance and Man-Biting Rate. Chi-square analysis showed significant difference in the abundance of Anopheles gambiae s.l. sibling species and Man-Biting Rate of molecular species in seasons (p<0.05). ANOVA showed significant difference in the monthly abundance of molecular species (p<0.05). The abundance of Anopheles gambiae s.l and presence of the molecular species and hybrid in the study-area is of epidemiological importance since the genetic variants are found to differ in ecological preference and susceptibility to pyrethroids.

Keywords: Anopheles gambiae s.l.; molecular forms; sibling species; vector control