Persistently high proportions of plasmodium-infected Anopheles funestus mosquitoes in two villages in the Kilombero valley, South-Eastern Tanzania

Salum A Mapua; Emmanuel E Hape; Japhet Kihonda; Hamis Bwanary; Khamis Kifungo; Masoud Kilalangongono; Emmanuel W Kaindoa; Halfan S Ngowo; Fredros O Okumu

doi:10.1016/j.parepi.2022.e00264

Persistently high proportions of plasmodium-infected Anopheles funestus mosquitoes in two villages in the Kilombero valley, South-Eastern Tanzania

Parasite Epidemiol Control. 2022 Aug 3:18:e00264. doi: 10.1016/j.parepi.2022.e00264. eCollection 2022 Aug.

Authors

Salum A Mapua^{1

2}, Emmanuel E Hape^{1

3}, Japhet Kihonda¹, Hamis Bwanary¹, Khamis Kifungo¹, Masoud Kilalangongono¹, Emmanuel W Kaindoa^{1

4}, Halfan S Ngowo^{1

3}, Fredros O Okumu^{1

5

3

4}

Affiliations

¹ Environmental Health and Ecological Sciences Department, Ifakara Health Institute, P. O. Box 53, Morogoro, Tanzania.
² Centre for Applied Entomology and Parasitology, School of Life Sciences, Keele University, Huxley Building, Keele, Staffordshire ST5 5BG, UK.
³ Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow G12 8QQ, UK.
⁴ School of Life Science and Bioengineering, The Nelson Mandela African Institution of Science and Technology, P. O. Box 447, Arusha, Tanzania.
⁵ School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.

Abstract

Background: In south-eastern Tanzania where insecticide-treated nets have been widely used for >20 years, malaria transmission has greatly reduced but remains highly heterogenous over small distances. This study investigated the seasonal prevalence of Plasmodium sporozoite infections in the two main malaria vector species, Anopheles funestus and Anopheles arabiensis for 34 months, starting January 2018 to November 2020.

Methods: Adult mosquitoes were collected using CDC-light traps and Prokopack aspirators inside local houses in Igumbiro and Sululu villages, where earlier surveys had found very high densities of An. funestus. Collected females were sorted by taxa, and the samples examined using ELISA assays for detecting Plasmodium circumsporozoite protein in their salivary glands.

Results: Of 7859 An. funestus tested, 4.6% (n = 365) were positive for Pf sporozoites in the salivary glands. On the contrary, only 0.4% (n = 9) of the 2382 An. arabiensis tested were positive. The sporozoite prevalence did not vary significantly between the villages or seasons. Similarly, the proportions of parous females of either species were not significantly different between the two villages (p > 0.05) but was slightly higher in An. funestus (0.50) than in An. arabiensis (0.42). Analysis of the 2020 data determined that An. funestus contributed 97.7% of all malaria transmitted in households in these two villages.

Conclusions: In contexts where individual vector species mediate most of the pathogen transmission, it may be most appropriate to pursue a species-focused approach to better understand the ecology of the dominant vectors and target them with effective interventions to suppress transmission. Despite the ongoing efforts on tackling malaria in the two study villages, there is still persistently high Plasmodium infection prevalence in local populations of An. funestus, which now carry ~97% of all malaria infections and mediates intense year-round transmission. Further reduction in malaria burden in these or other similar settings requires effective targeting of An. funestus.

Keywords: Anopheles funestus; CDC, Centers for Diseases Control and Prevention; ELISA, Enzyme-Linked Immunosorbent Assay; GLM, Generalized Linear Model; GLMM, Generalized Linear Mixed Model; IRS, Indoor Residual Spraying; ITN, Insecticide-Treated Net; Ifakara health institute; Kilombero valley; LLINs, Long-Lasting Insecticidal Nets; Malaria transmission; NMSP, National Malaria Strategic Plan; PCR, Polymerase Chain Reaction; Pf-CSP, Plasmodium falciparum Circumsporozoite Protein; Plasmodium; Sporozoite prevalence; Tanzania.