Relationships between biological age, distance from aquatic habitats and pyrethroid resistance status of Anopheles funestus mosquitoes in south-eastern Tanzania

Pinda, P. G. et al. (2022) Relationships between biological age, distance from aquatic habitats and pyrethroid resistance status of Anopheles funestus mosquitoes in south-eastern Tanzania. Malaria Journal, 21, 365. (doi: 10.1186/s12936-022-04389-y) (PMID:36461058) (PMCID:PMC9719249)

Abstract

Background: Malaria transmission can be highly heterogeneous between and within localities, and is influenced by factors such as survival and biting frequencies of Anopheles mosquitoes. This study investigated the relationships between the biological age, distance from aquatic habitats and pyrethroid resistance status of Anopheles funestus mosquitoes, which currently dominate malaria transmission in south-east Tanzania. The study also examined how such relationships may influence malaria transmission and control. Methods: Female An. funestus were collected in houses located 50–100 m, 150–200 m or over 200 m from the nearest known aquatic habitats. The mosquitoes were exposed to 1×, 5× and 10× the diagnostic doses of deltamethrin or permethrin, or to the synergist, piperonyl butoxide (PBO) followed by the pyrethroids, then monitored for 24 h-mortality. Ovaries of exposed and non-exposed mosquitoes were dissected to assess parity as a proxy for biological age. Adults emerging from larval collections in the same villages were tested against the same insecticides at 3–5, 8–11 or 17–20 days old. Findings: Mosquitoes collected nearest to the aquatic habitats (50-100 m) had the lowest mortalities compared to other distances, with a maximum of 51% mortality at 10× permethrin. For the age-synchronized mosquitoes collected as larvae, the insecticide-induced mortality assessed at both the diagnostic and multiplicative doses (1×, 5× and 10×) increased with mosquito age. The highest mortalities at 1× doses were observed among the oldest mosquitoes (17–20 days). At 10× doses, mortalities were 99% (permethrin) and 76% (deltamethrin) among 8–11 day-olds compared to 80% (permethrin) and 58% (deltamethrin) among 3–5 day-olds. Pre-exposure to PBO increased the potency of both pyrethroids. The proportion of parous females was highest among mosquitoes collected farthest from the habitats. Conclusion: In this specific setting, older An. funestus and those collected farthest from the aquatic habitats (near the centre of the village) were more susceptible to pyrethroids than the younger ones and those caught nearest to the habitats. These findings suggest that pyrethroid-based interventions may remain at least moderately effective despite widespread pyrethroid-resistance, by killing the older, less-resistant and potentially-infective mosquitoes. Further studies should investigate how and whether these observations could be exploited to optimize malaria control in different settings.

• Item Type: Articles
• Additional Information: The activities in this work were supported by Anopheles funestus 100, a Grant from the Bill & Melinda Gates Foundation (INV-002138). PP and FOO were supported by Howard Hughes International Scholarship (OPP1099295). LLK was supported by a DST/NRF South African Research Chairs Initiative Grant (UID 64763).
• Keywords: Insecticide resistance, mosquito age, parity, age grading, Anopheles funestus, piperonyl butoxide, malaria, aquatic habitats.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ngowo, Halfan and Okumu, Professor Fredros and Mshani, Mr Issa
• Authors: Pinda, P. G., Msaky, D. S., Muyaga, L. L., Mshani, I. H., Njalambaha, R. M., Kihonda, J., Bwanaly, H., Ngowo, H. S., Kaindoa, E. W., Koekemoer, L. L., and Okumu, F. O.
• College/School: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Journal Name: Malaria Journal
• Publisher: BioMed Central
• ISSN: 1475-2875
• ISSN (Online): 1475-2875
• Copyright Holders: Copyright © 2022 The Authors
• First Published: First published in Malaria Journal 21: 365
• Publisher Policy: Reproduced under a Creative Commons License