Evaluation of potential vector control methods that target outdoor feeding anopheles mosquitoes
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Date
2017
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Publisher
Sokoine University of Agriculture
Abstract
Insecticide-Treated Nets (ITNs/Long Lasting Insecticide-Treated Nets (LLINs) and
Indoor Residual Spraying (IRS) have contributed to halving global malaria incidence and
mortality rates. Achieving zero malaria transmission using these methods which target
indoor-feeding mosquitoes is hampered by residual malaria transmission attributable to
outdoor-feeding mosquitoes. This study evaluated potential malaria vector-control
methods that target outdoor-feeding Anopheles mosquitoes to contribute to efforts to
eliminate residual malaria transmission. Specifically, it set out: (i) To assess community
knowledge and awareness on malaria and its vectors, (ii) To determine spatial distribution
of Anopheles adults and larvae, (iii) To determine effects of combined use of
chemo-attractants and non excito-repellant insecticide (Chlorfenapyr) applied to
contaminating devices in attracting and killing outdoor Anopheles mosquitoes and (iv) To
evaluate method of attracting gravid Anopheles gambiae s.s to oviposit in
artificially-created ovicidal breeding sites. To meet specific objective (i), a cross-sectional
questionnaire study which explored knowledge and awareness on malaria was carried out
in Dodoma and Morogoro on 400 respondents. The questionnaire study revealed that a
vast majority (78.8%) were not aware that early outdoor biting of mosquito was a risk
factor for malaria transmission. The main Anopheles breeding sites were found to be rice
paddies (25.2%), ditches (23.3%) and septic tanks/pits (18.8%). Adult Anopheles
mosquitoes were collected mainly from ceiling (42.3%) and stored/piled junks (16.3%) in
the hot-wet season and from under beds (32.1%), undisturbed curtains (25.3%) and store
rooms (23.7%) in cold-dry seasons. On testing a novel Umbrella-topped Mosquito
Contaminating Device (UtMCD) developed in the present studies as a tool for attracting
and killing outdoor Anopheles mosquitoes (specific objective iii) it was revealed that,
adjusting for season and study location, the number of Anopheles mosquitoes caught were
significantly associated with type of UtMCD set-up used. From among the UtMCD set-ups A-D and device E tested (A: Device alone, B: Device with attractants alone, C:
Device with insecticide alone, D: Device with insecticide and attractants and E: Device
(Okomu), UtMCD set-up D significantly caught more Anopheles mosquitoes than
UtMCD set-up A (AMR=2.96,p<0.0001). Mortality analysis showed that UtMCD set-ups
D, C and device E had higher percentage mortality: D (87.7%); C (89.4%) and E (84.9%)
than UtMCD set-up A (19.2%) and UtMCD set-up B (17.4%). In the studies on
artificially-created breeding sites it was found that the odds of not hatching for eggs
deposited in hay infusion +vinegar sites was significantly greater than that of eggs
deposited in water alone (AOR=80.6, p<0.001). In conclusion, the studies revealed there
is a need for increased awareness on malaria transmission by outdoor early-feeding
Anopheles and furthermore, the novel UtMCD (with chemo-attractants and insecticide) as
well as artificial breeding sites with attractants and an ovicidal agent (vinegar) have
potential for use in integrated vector and larval source management to eliminate residual
malaria transmission.
Description
MSc.Dissertation
Keywords
Zero malaria transmission, Insecticide treated nets, Malaria vector control, Anopheles mosquitoes, Dodoma region, Morogoro region