Species Characterization and Determination of Phenotypic Insecticide Resistance Profile of Secondary Vectors of Malaria Transmission in Kisumu County, Kenya
Mustapha, Mahamat Amine
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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.