Abundance, Distribution and Insecticide Resistance of Anopheles Mosquitoes (Diptera: Culicidae) and Malaria Transmission Intensity in Relation to Agro-ecology in Sekoru District, Southwestern Ethiopia
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Date
2017-06
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Addis Ababa University
Abstract
Malaria is a leading cause of morbidity and mortality in several sub-Saharan African
countries. Environmental/ecological changes due to anthropogenic activities are among
the determinant factors for malaria transmission. Agricultural practices are among
anthropogenic activities that contribute to malaria incidence and transmission.
Understanding association of ecological changes due to anthropogenic activities on
mosquito species composition, abundance, distribution, dynamics, insecticide resistance
and malaria transmission intensity is important to plan and implement effective vector
control intervention strategies. Thus, the aim of this study was to investigate species
composition, abundance, distribution and infectious rate of Anopheles mosquitoes and
their knockdown resistance (kdr) status in relation to agricultural practices. A
longitudinal entomological study was conducted from January to December 2015 in
Sekoru District, southwestern Ethiopia. Anopheles mosquito larvae and adults were
collected using different methods from villages with different agro-ecology. The
mosquitoes were identified to species level using standard keys. Molecular identification
of Anopheles gambiae complex and detection of knockdown insecticide resistance (kdr)
was conducted using species-specific PCR and allele specific PCR techniques. Moreover,
Plasmodium circumsporozoite protein was detected for both Plasmodium falciparum and
P. vivax using Enzyme-linked Immunosorbent Assay (ELISA). Eight Anopheles
mosquito species (Anophelesarabiensis,An. demeilloni, An. squamosus, An. garnhami,
An. christyi, An. pretoriensis, An. longipalpis and An. marshallii) were identified, of
which An. arabiensis was the predominant species (46.2%; n=715). The highest number
of Anopheles mosquitoes (66%; n=1019) was collected from the irrigated village. The
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infection rate of An. arabiensis was higher in the irrigated village (10.8 infective
bites/person/month) as compared to rain fed agriculture practicing village (5.99 infective
bites/person/month) and human settlement village (zero infective bite). Anopheles
gambiaes.l. larvae were the predominant (57.4%) larval species identified. The highest
larval density (2.12 larvae/dip) was recorded from the irrigated village. Only West
African kdr mutation (L1014F) was detected with an allelic frequency of 83.88%. The
distribution and frequency of kdr allele were significantly associated with study villages
(X2=133.85, df=2, P <0.001). The kdr allele frequency was 95%in the irrigated village,
78.87%in village with rain fed agriculture, and 3.89% in the human settlement village. In
conclusion, Anopheles mosquito abundance, distribution, infection rate and insecticide
resistance were significantly associated with agro-ecology. Agro-ecological practices
need to be considered in the management of Anopheles vectors of malaria.
Keywords: Anopheles mosquitoes, Agro-ecology, Insecticide resistance, Irrigation,
Larval habitats, Malaria, Sekoru District
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Keywords
Anopheles Mosquitoes, Agro-Ecology, Insecticide Resistance, Larval HaIrrigationbitats, Malaria, Sekoru District