Swarms of the malaria vector Anopheles funestus in Tanzania

Abstract

BackgroundAnopheles funestus mosquitoes currently contribute more than 85% of ongoing malaria transmission events in south-eastern Tanzania, even though they occur in lower densities than other vectors, such as Anopheles arabiensis. Unfortunately, the species ecology is minimally understood, partly because of difficulties in laboratory colonization. This study describes the first observations of An. funestus swarms in Tanzania, possibly heralding new opportunities for control.MethodUsing systematic searches by community-based volunteers and expert entomologists, An. funestus swarms were identified in two villages in Ulanga and Kilombero districts in south-eastern Tanzania, starting June 2018. Swarms were characterized by size, height, start- and end-times, presence of copulation and associated environmental features. Samples of male mosquitoes from the swarms were examined for sexual maturity by observing genitalia rotation, species identity using polymerase chain reaction and wing sizes.Results581 An. funestus (98.1% males (n = 570) and 1.9% (n = 11) females) and 9 Anopheles gambiae sensu lato (s.l.) males were sampled using sweep nets from the 81 confirmed swarms in two villages (Ikwambi in Kilombero district and Tulizamoyo in Ulanga district). Six copulation events were observed in the swarms. Mean density (95% CL) of An. funestus caught/swarm/village/evening was 6.6 (5.9–7.2) in Tulizamoyo and 10.8 (5.8–15.8) in Ikwambi. 87.7% (n = 71) of the swarms were found in Tulizamoyo, while 12.3% (n = 10) were in Ikwambi. Mean height of swarms was 1.7 m (0.9–2.5 m), while mean duration was 12.9 (7.9–17.9) minutes. The PCR analysis confirmed that 100% of all An. funestus s.l. samples processed were An. funestus sensu stricto. Mean wing length of An. funestus males was 2.47 mm (2.0–2.8 mm), but there was no difference between swarming males and indoor-resting males. Most swarms (95.0%) occurred above bare ground, sometime on front lawns near human dwellings, and repeatedly in the same locations.ConclusionThis study has demonstrated occurrence of An. funestus swarms for the first time in Tanzania. Further investigations could identify new opportunities for improved control of this dominant malaria vector, possibly by targeting the swarms.

Opinions of key stakeholders on alternative interventions for malaria control and elimination in Tanzania

“…Swarms usually occur at approximately the same time, usually at sunset, and repeatedly at same locations throughout the year [47]. Studies done in Burkina Faso and Tanzania have shown that Anopheles mosquito swarms can be located and targeted, and are effective in reducing overall mosquito density [21][22][23] Modified mosquitoes This intervention refers to alterations of mosquito genes or physiology for the purpose of reducing their competence in diseases transmission. The modified mosquitoes are released into the environment so that they can interbreed with the wild mosquitoes and, depending on the trait they carry, either reduce the density of malaria vectors or replace its population with mosquitoes unable to transmit the pathogen.…”

“…Several complementary vector control interventions are currently being discussed as possible candidates to accelerate the malaria elimination efforts [12]. Examples include: (a) larval source management (LSM), including larviciding and environmental management [13,14], (b) topical repellents for personal protection [15,16], (c) mass drug administration with endectocides such as ivermectin [17,18], (d) use of mosquito modification techniques, either to suppress or replace vector populations [19,20], (e) outdoor targeting of male mosquitoes through insecticide-spraying of mosquito swarms [21][22][23], (f ) housing improvement measures such as better window screening and improved house designs [24][25][26], (g) spatial repellents able to protect multiple individuals over wide areas [27,28], (h) attractive toxic sugar baits targeting sugar-seeking mosquitoes [29,30], and (i) mosquito-killing fungal spores and toxins [31,32].…”

Motivations and expectations driving community participation in entomological research projects: Target Malaria as a case study in Bana, Western Burkina Faso

“…Community participation is considered essential for attaining an effective control of disease vectors [19], and multiple studies attest to the importance of enrolling local residents in campaigns against mosquitoes in particular [20][21][22][23][24]. Unfortunately, these studies provide limited information on the factors that motivate local communities to become actively involved in these interventions, and the question of which particular expectations and considerations drive public participation remains as a result underinvestigated.…”

Motivations and expectations driving community participation in entomological research projects: Target Malaria as a case study in Bana, Western Burkina Faso

“…Community participation is considered essential for attaining an effective control of disease vectors [19], and multiple studies attest to the importance of enrolling local residents in campaigns against mosquito vectors in particular [20][21][22][23][24]. Unfortunately, these studies provide limited information on the factors that motivate local communities to become actively involved in health programmes, and the question of which particular expectations and considerations drive public participation remains as a result under-investigated.…”