Aquatic habitats of the malaria vector Anopheles funestus in rural south-eastern Tanzania

Ismail H Nambunga,Marceline F Finda,Halfan S Ngowo,Gerald Z Tamayamali,Nicolaus T Mhumbira,Emmanuel E Hape,Salum A Mapua,Rukiyah M Njalambaha,Fredros O Okumu,Dickson W Lwetoijera,Nicodem J Govella,Karim R Mchwembo,Dickson S Msaky,Betwel J Msugupakulya,Damaris Matoke-Muhia,Emmanuel W Kaindoa,Slyakus V Mlembe

doi:10.1186/s12936-020-03295-5

Abstract

BackgroundIn rural south-eastern Tanzania, Anopheles funestus is a major malaria vector, and has been implicated in nearly 90% of all infective bites. Unfortunately, little is known about the natural ecological requirements and survival strategies of this mosquito species.MethodsPotential mosquito aquatic habitats were systematically searched along 1000 m transects from the centres of six villages in south-eastern Tanzania. All water bodies were geo-referenced, characterized and examined for presence of Anopheles larvae using standard 350 mLs dippers or 10 L buckets. Larvae were collected for rearing, and the emergent adults identified to confirm habitats containing An. funestus.ResultsOne hundred and eleven habitats were identified and assessed from the first five villages (all < 300 m altitude). Of these, 36 (32.4%) had An. funestus co-occurring with other mosquito species. Another 47 (42.3%) had other Anopheles species and/or culicines, but not An. funestus, and 28 (25.2%) had no mosquitoes. There were three main habitat types occupied by An. funestus, namely: (a) small spring-fed pools with well-defined perimeters (36.1%), (b) medium-sized natural ponds retaining water most of the year (16.7%), and (c) slow-moving waters along river tributaries (47.2%). The habitats generally had clear waters with emergent surface vegetation, depths > 0.5 m and distances < 100 m from human dwellings. They were permanent or semi-permanent, retaining water most of the year. Water temperatures ranged from 25.2 to 28.8 °C, pH from 6.5 to 6.7, turbidity from 26.6 to 54.8 NTU and total dissolved solids from 60.5 to 80.3 mg/L. In the sixth village (altitude > 400 m), very high densities of An. funestus were found along rivers with slow-moving clear waters and emergent vegetation.ConclusionThis study has documented the diversity and key characteristics of aquatic habitats of An. funestus across villages in south-eastern Tanzania, and will form an important basis for further studies to improve malaria control. The observations suggest that An. funestus habitats in the area can indeed be described as fixed, few and findable based on their unique characteristics. Future studies should investigate the potential of targeting these habitats with larviciding or larval source management to complement malaria control efforts in areas dominated by this vector species.

Highlights

In rural south-eastern Tanzania, Anopheles funestus is a major malaria vector, and has been implicated in nearly 90% of all infective bites
Its dominance in pathogen transmission [4, 7] is attributable to factors such as: (a) being predominantly anthropophilic and endophilic [8, 9], (b) their resistance to some of the commonly-used pyrethroid insecticides in locations such as south-eastern Tanzania [10,11,12,13,14], and (c) their superior daily survival probabilities as reflected in the higher parity rates compared to other Anopheles species [4, 5, 7]
This study provides a basis for designing future surveys and control operations targeting malaria, especially in places such as south-eastern Tanzania where An. funestus and An. arabiensis play a major role in malaria transmission [5, 6, 28,29,30]

Summary

Introduction

In rural south-eastern Tanzania, Anopheles funestus is a major malaria vector, and has been implicated in nearly 90% of all infective bites. The supremacy of An. funestus in malaria transmission has been observed even in areas where they occur at far lower densities compared to other malaria vectors, such as Anopheles arabiensis [4, 5, 15]. In such settings, the infrequent occurrence partly explains why their behaviours are relatively understudied in the field. Researchers, sometimes rely on adult collections rather than larval collections to obtain enough samples for insecticide resistance testing [4], which according to the World Health Organization (WHO) protocols require F1 offspring with synchronized age groups [16]

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Results

Discussion

Conclusion