Fine-scale distribution of malaria mosquitoes biting or resting outside human dwellings in three low-altitude Tanzanian villages

Mmbando, A. S. et al. (2021) Fine-scale distribution of malaria mosquitoes biting or resting outside human dwellings in three low-altitude Tanzanian villages. PLoS ONE, 16(1), e0245750. (doi: 10.1371/journal.pone.0245750) (PMID:33507908) (PMCID:PMC7842886)

Abstract

Background: While malaria transmission in Africa still happens primarily inside houses, there is a substantial proportion of Anopheles mosquitoes that bite or rest outdoors. This situation may compromise the performance of indoor insecticidal interventions such as insecticide-treated nets (ITNs). This study investigated the distribution of malaria mosquitoes biting or resting outside dwellings in three low-altitude villages in south-eastern Tanzania. The likelihood of malaria infections outdoors was also assessed. Methods: Nightly trapping was done outdoors for 12 months to collect resting mosquitoes (using resting bucket traps) and host-seeking mosquitoes (using odour-baited Suna® traps). The mosquitoes were sorted by species and physiological states. Pooled samples of Anopheles were tested to estimate proportions infected with Plasmodium falciparum parasites, estimate proportions carrying human blood as opposed to other vertebrate blood and identify sibling species in the Anopheles gambiae complex and An. funestus group. Environmental and anthropogenic factors were observed and recorded within 100 meters from each trapping positions. Generalised additive models were used to investigate relationships between these variables and vector densities, produce predictive maps of expected abundance and compare outcomes within and between villages. Results: A high degree of fine-scale heterogeneity in Anopheles densities was observed between and within villages. Water bodies covered with vegetation were associated with 22% higher densities of An. arabiensis and 51% lower densities of An. funestus. Increasing densities of houses and people outdoors were both associated with reduced densities of An. arabiensis and An. funestus. Vector densities were highest around the end of the rainy season and beginning of the dry seasons. More than half (14) 58.3% of blood-fed An. arabiensis had bovine blood, (6) 25% had human blood. None of the Anopheles mosquitoes caught outdoors was found infected with malaria parasites. Conclusion: Outdoor densities of both host-seeking and resting Anopheles mosquitoes had significant heterogeneities between and within villages, and were influenced by multiple environmental and anthropogenic factors. Despite the high Anopheles densities outside dwellings, the substantial proportion of non-human blood-meals and absence of malaria-infected mosquitoes after 12 months of nightly trapping suggests very low-levels of outdoor malaria transmission in these villages.

• Item Type: Articles
• Additional Information: Fredros Okumu was funded by the Wellcome Trust Intermediate Research Fellowship (Grant number: WT102350/Z/13/Z) which funded this research. Arnold Mmbando was also supported by the Wellcome Trust Masters Fellowship in Public Health and the Association of Physicians of Great Britain and Ireland for funding this research (Grant number 106356/Z/14/Z).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ngowo, Halfan and Okumu, Professor Fredros and Nelli, Dr Luca

Creator Roles

Ngowo, H. S.: Formal analysis, Writing – review and editing
Okumu, F. O.: Conceptualization, Data curation, Funding acquisition, Investigation, Methodology, Resources, Supervision, Visualization, Writing – original draft, Writing – review and editing
Nelli, L.: Formal analysis, Writing – original draft, Writing – review and editing

• Authors: Mmbando, A. S., Kaindoa, E. W., Ngowo, H. S., Swai, J. K., Matowo, N. S., Kilalangongono, M., Lingamba, G. P., Mgando, J. P., Namango, I. H., Okumu, F. O., and Nelli, L.
• Subjects: Q Science > QH Natural history > QH301 Biology; Q Science > QL Zoology
• College/School: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Journal Name: PLoS ONE
• Publisher: Public Library of Science
• ISSN: 1932-6203
• ISSN (Online): 1932-6203
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in PLoS ONE 16(1):e0245750
• Publisher Policy: Reproduced under a Creative Commons License