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

Abstract

Background In 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.Methods Potential 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 350mls dippers or 10L buckets. Larvae were collected for rearing, and the emergent adults identified to confirm habitats containing An. funestus.Results One hundred and eleven (111) habitats were identified and assessed from the first five villages (all <300m 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 > 0.5m and distances < 100m 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 >400m), very high densities of An. funestus were found along rivers with slow-moving clear waters and emergent vegetation.Conclusion This 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.

Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

“…gambiae s.l. [48,[55][56][57], so we do not think biased habitat sampling can explain the low abundance of primary vector species detected. Combined sampling of larval habitat and adults will be needed to further resolve the dynamic relationships among primary and secondary vector populations around villages and across the wider landscape.…”

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

“…Indeed, An . funestus in this region is now known to prefer permanent or semi-permanent water with emergent vegetation situated at least 100m from the human dwellings [ 44 ] ( S4 Fig ). The map grids point comprised of season swamps has positive associations with An .…”

“…Similarly, wetlands did not seem to affect An . funestus mosquito densities, as this species prefers to breed in the permanent and deep water bodies [ 43 , 44 ] ( S11 Fig ) ( Table 2 & Supplementary materials).…”

“…One possible explanation for this is that most of the rice fields found in the study area were closer to human houses, and proximity to human settlements has been observed as a factor favouring An . funestus breeding habitats [ 44 ]. The rice cultivation performed in this study area involves a considerable use of pesticides, which are also likely to have an effect on mosquitoes susceptibility to insecticides [ 45 ].…”

“…An . funestus however exhibited less fluctuation compared to other malaria vectors, most likely due to its preference for semi-permanent or permanent habitats [ 44 ]. Also, this is another sign of heterogeneity of malaria vector densities at small scale and that there may be more factors influencing these densities than we assessed.…”