Species Characterization and Determination of Phenotypic Insecticide Resistance Profile of Secondary Vectors of Malaria Transmission in Kisumu County, Kenya
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Date
2022
Authors
Mustapha, Mahamat Amine
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
he control of malaria vector has been realised primarily via indoor interventions.
These control measures are aimed at primary vectors ensuing in malaria vector
population drop. Because of their principal exophagic and exophilic behaviour,
current indoor control measures leave out secondary vectors. This indicates a high
likelihood that relative input of transmission by secondary malaria vectors is large.
With past attention based on primary vectors, there is scanty information on
secondary malaria vectors in numerous nations in Africa. The purpose of the study
was to establish the species compositions and proportions of secondary vectors
infected with Plasmodium falciparum as well as the phenotypic insecticide resistance,
of secondary malaria vectors. Cross-sectional sampling of adult Anopheles was
achieved by means of indoor and outdoor Centre of Diseases Control light traps and
animal-baited traps in Kakola Ombaka and Kisian, whereas larvae were collected in
Ahero. Secondary vectors caught were exposed to permethrin using WHO bioassays
and then evaluated by Enzyme-linked Immunosorbent Assay (ELISA) to check for
proportions infected with P. falciparum sporozoites. All Anopheles were classified to
species level using morphological keys with a subset being molecularly identified
using ITS2 and CO1 sequencing for species categorisation. Chi square test was used
to compute the difference between outdoor and indoor malaria vector mosquito
density. A t-test was employed to compare captures from light traps and animal bait
trap. The infection rate was figured as the proportion of sporozoite positive mosquito
samples divided by the sum of molecularly identified samples. Basic Local Alignment
Search Tool was used to analysis sequence data. The density of secondary malaria
vectors was calculated as the quantity of adult female malaria vectors per trapping per
night for each and every capture method. Two morphologically identified secondary
vectors were seized—An. coustani and An. pharoensis. Subsequent molecular
characterization revealed them to be four distinct species. These encompassed a
species with 100% ITS2 similarities to An. christyi. Another species had 100%
similarity to An. sp. 15 BSL-2014. An unidentified member with 76% ITS2 similarity
to An. coustani complex (An. cf. coustani) was also found. Finally a species with
100% ITS2 similarity to that of An. pharoensis and An. squamosus (An. cf.
pharoensis) were identified. Standardized (Anopheles per trap per night) capture rates
revealed higher proportions of secondary vectors through most trapping methods with
indoor, outdoor CDC-LTs and ABT captures consisting of 52.2% (n = 93), 78.9% (n
= 221) and 58.1% (n = 573) secondary vectors correspondingly. Bionomic traits of
captured secondary vectors species revealed them to be predominantly outdoor
resting. Secondary malaria species captured indoor showed indoor resting behaviour
remarkably proportional to primary vectors. Based on CDC-LT capture secondary
malaria vectors had biting rates similar to those of primary vectors overall. The
overall percentage of secondary vectors with P. falciparum sporozoite was 0.63% (n =
5), with the unidentified species An. cf. pharoensis, established to carry Plasmodium.
Overall secondary vectors were susceptible to permethrin with a > 99% mortality rate.
Several bionomic traits indicate that secondary vectors might add significantly to
malaria transmission. These traits include, high densities, endophily behaviour
comparable to primary vectors, higher exophily and Plasmodium positive proportions.
The study endorses broadening malaria control measures to include outdoor
secondary malaria vectors. Unidentified species shows the necessity for additional
morphological and molecular identification studies towards further characterization.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of a Degree in Master of Science (Biotechnology) in the School of Pure and Applied Sciences of Kenyatta University, March 2022
Keywords
Species Characterization, Determination, Phenotypic, Insecticide Resistance Profile, Secondary Vectors, Malaria Transmission, Kisumu County, Kenya