Identification of the Anopheles marshallii group and vector species composition in the forest ecozone of Akwa Ibom State, Southern Nigeria.

BACKGROUND: Accurate vector species identification is essential to distinguish the co-existence of primary and secondary vectors of malaria sustaining transmission in different settings. This evaluation reviews the identity, bionomics, and behaviour of malaria vectors where composition shifted in the forest ecological zone in Mkpat-Enin Local Government Area of Akwa Ibom State, Nigeria. METHODS: Anopheline mosquito samples were collected from pyrethrum spray catch collections and CDC light traps from 2016 through 2022. Samples were morphologically identified and subjected to polymerase chain reaction assays and sequencing analysis to confirm the identity of unamplified and/or misidentified samples. Mosquito bionomics such as abundance, indoor and outdoor human biting rates (HHR), indoor resting density (IRD), biting time, Plasmodium falciparum infection and blood meal sources of the mosquito samples were determined from the 2021 and 2022 samples. Data analysis was performed using one-way ANOVA (analysis of variance) tests and chi-square tests in GraphPad Prism version 9.0. RESULTS: A total of eight Anopheles species were identified: Anopheles coustani, Anopheles funestus group, Anopheles gambiae sensu lato (s.l.), Anopheles maculipalpis, Anopheles marshallii group, Anopheles moucheti, Anopheles nili, and Anopheles obscurus. The outcome of the analysed data confirmed a shift in the composition from An. gambiae s.l. to the An. marshallii group. The IRD, indoor and outdoor HBR of the An. marshallii group were not significantly different from that of An. gambiae s.l. in 2021 (p > 0.05) but significantly higher in 2022 (p < 0.05). The peak indoor and outdoor HBR of the An. marshallii group were observed to be higher than those of An. gambiae s.l. during the dry season. In both years, the An. gambiae s.l. and the An. marshallii group mosquitoes showed comparable preference for bovine blood meal. The preference for human blood meal was not significantly different (p = 0.21) between both species. The An. marshallii group was found to have been infected with Plasmodium falciparum sporozoites (n = 2) alongside An. gambiae sensu stricto (s.s.) (n = 1) and Anopheles coluzzii (n = 2). CONCLUSION: The An. marshallii group was confirmed as an abundant malaria vector species in. Mkpat-Enin Local Government Area of Akwa Ibom State. While similar indoor vector control interventions are recommended for both species; other interventions may be needed to address the early evening outdoor biting observed in the An. marshallii group.