Insecticide Resistance And Its Impact On Malaria Transmission Potential Among The Major Vectors In Teso Sub – Counties, Western Kenya
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Date
2020Author
Githinji, Edward K
Type
ThesisLanguage
enMetadata
Show full item recordAbstract
In Africa, knockdown resistance (kdr) is strongly linked to pyrethroid insecticide resistance in
Anopheles gambiae s.l; which may have vital implications to the current up-scaled indoor residual
spraying (IRS) and pyrethroid-treated bed net campaigns. This investigation proposed to evaluate
the extent and levels of insecticide resistance among major vectors in Teso North and South sub
counties, western Kenya, and its impact on entomological parameters of malaria transmission. For
WHO phenotypic susceptibility tube assay, mosquito larvae were sampled using a dipper, reared
into 3-5 days-old females which were exposed to 0.75% permethrin, 0.05% deltamethrin and 0.1%
bendiocarb. Random sampling of adult mosquitoes [3448] was done using adult mosquito
sampling methods. Abdominal statuses, parity rates, age grading and molecular species
identification were recorded. Kdr East TaqMan PCR probed for the mutant allele and wild type.
Sporozoite ELISA detected circum-sporozoite protein. Anopheles gambiae sensu stricto were the
significant majority in terms of species composition at 78.9% as compared to Anopheles arabiensis
(20.7%) [t (4, 4) = 11.1268, p < .05]. Highest proportion of SS alleles (86.1%) was also found
among Anopheles gambiae sensu stricto mosquitoes. Susceptible Kengatunyi cluster had higher
proportion of An. arabiensis than resistant Rwatama. Bendiocarb caused 100% mortality while
deltamethrin had higher insecticidal effects (77%) on female mosquitoes than permethrin (71%).
There was a significant difference in SS allele frequencies between Kengatunyi (57.8%) and
Rwatama (93.4%). Of the parous vectors, 75.6% were homozygous resistant, 2.4% were
heterozygous and 22% were homozygous susceptible. Mosquitoes in the resistant cluster had an
average lifespan of 16 days compared to 5 days in the susceptible cluster. Resistant clusters had
the largest number of infective bites per person per night at 0.4. Of the sporozoite positive
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mosquitoes, 71.4% were homozygous resistant and the rest homozygous susceptible.
Heterozygous LS allelic vectors had significantly higher affinity for bovine blood while SS allelic
vectors had significant higher affinity for human blood. All SS, LS and LL carriers were biting
more at dawn than at dusk. All results were significant at p<0.05. Most likely, the higher the
selection pressure exerted indoors by insecticidal nets the higher were the resistance alleles. Use
of pyrethroids impregnated nets and agrochemicals may have caused female mosquitoes to select
for pyrethroid resistance, consequently impacted on species composition and behaviour patterns.
Confirmed phenotypic and genotypic insecticide resistance in major malaria vectors in Teso North
and Teso South sub counties, impacted significantly on vector species composition, age structure,
density, infectivity, feeding and resting behaviours. Insecticide resistance management practices
in Kenya should be fastracked and harmonised with agricultural sector agrochemical based
activities and possibly switch to carbamate usage. The implication of such high resistance levels
in the mosquitoes is that resistance is likely to persist and or even increase if mono-molecules of
permethrin and deltamethrin or both continue to be used in all net and non-net based mosquito
control purposes. Piperonyl butoxide (PBO) that prohibit certain metabolic enzymes within
malaria vectors and has been combined into pyrethroid-LLINs to create pyrethroid-PBO nets, may
be an extremely viable option against the spread of insecticide resistance in Kenya.
Key words: Anopheles species Insecticide resistance WHO tube assay
kdr Genotypic frequency
Publisher
University of Nairobi
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Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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