Department Of Zoology

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    Significant 24 h recovery and survival of Culex mosquitoes exposed to pyrethroid insecticides using the CDC bottle bioassay
    (2023) Abiodun Obembe
    Insecticides deployed for mosquito vector control rely on the susceptibility of the targeted vector population for continued efficacy and public health protection. The Centers for Disease Control and Prevention (CDC) bottle bioassay is a standard method used for rapid mosquito insecticide resistance assessment without measuring sublethal or delayed insecticidal effects. Ignored sublethal or delayed mortality effects may affect the accuracy of susceptibility test outcomes and appropriateness of insecticide selection decisions. This study found significant recovery and survival among Culex mosquito populations initially immobilized after pyrethroid insecticide exposures using the CDC bottle bioassay. Adult female Culex mosquitoes, reared from three different larval collection sites, were exposed to x1 and x2 intensities of deltamethrin and alphacypermethrin insecticides using the CDC bottle bioassay method. Exposed mosquitoes were held for 24 hours for comparison of 30 min exposure time and 24 h post-exposure mortalities. Subsamples of exposed mosquitoes were identified with Polymerase Chain Reaction (PCR) technique. For both x1 (P ≤ 0.009) and x2 (P ≤ 0.048) insecticide intensities, the percentage mosquito mortalities at 30 min exposure time (20-24%, 21-27%) reduced significantly after the 24 h postexposure period (3-9%, 6-13%) respectively. However, after both 30 min (P ≥ 0.475) and 24 h (P ≥ 0.090) periods, mosquito mortalities at x2 intensity (21-27%, 6-13%) were not significantly higher than mortality at x1 (20-24%, 3-9%). All PCR-identified samples were found to be Culex quinquefasciatus. The significantly reduced mortality at 24 h post exposure time indicates delayed recovery and survival of mosquitoes, usually not captured when using the CDC bottle bioassay method. This result provides evidence to suggest further discussions and review of the CDC bottle bioassay procedures for improved measure of mosquito susceptibility/resistance.
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    Multiple Pyrethroid Resistance in Urban Male and Female An. gambiae s.l Populations in Ilorin Nigeria: Implications for Swarm Spraying and Toxic Sugar Bait Malaria Vec-tor Control
    (2023) Obembe et al
    Background: Male mosquito control through swarm spraying and Attractive Toxic Sugar Baits (ATSB) have been identified as potential strategies to complement the regular but insufficient female mosquito-based insecticide-treated net (ITN) approach. However, the effectiveness of these control strategies relies on under-standing the insecticide susceptibility status of the targeted male and female mosquito populations. There-fore, this study aimed to assess the insecticide susceptibility status of male and female An. gambiae s.l. Popu-lations in urban Ilorin, Nigeria. Methods: Using WHO kits and protocol, adult male and female mosquitoes reared from the same larval col-lections from different sites were exposed separately to permethrin, deltamethrin, and alphacypermethrin insecticides. Joint insecticide susceptibility tests, involving exposures of equal numbers of male and female mosquitoes to each insecticide, were also conducted in anticipation of joint insecticide exposure on the field. Exposed mosquitoes were identified to species level. Results: Higher kdt50s (52.5-641.3mins) and lower mortalities (permethrin 39-62%, deltamethrin 57-68%, alphacypermethrin 44-60%), indicating higher levels of resistance, were observed for the females compared to the male (22.1-42.2 mins, 60-94%) mosquitoes. The percentage mortalities of males (71-94%) were sig-nificantly (P ≤ 0.043) higher than those of the jointly exposed females (39-62%). However, separately ex-posed male mosquito mortalities (60-81%) were not significantly (P ≥ 0.067) higher than the females (55-68%). All the male mosquito populations were resistant to permethrin (75-94% mortality), deltamethrin (60-82%), and alphacypermethrin (74-86%) insecticides after joint and separate exposures. Resistant male and female mosquitoes were identified predominantly as An. arabiensis (74-84%). Conclusion: Multiple pyrethroid insecticide resistance detected in the male and female mosquito populations indicates the potential ineffectiveness of pyrethroid-based swarm spraying, pyrethroid ATSB and ITNs in the study location
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    Spatial distribution and ecological niche modeling of geographical spread of Anopheles gambiae complex in Nigeria using real time data
    (2023-08-22) Adeogun et al
    The need for evidence-based data, to inform policy decisions on malaria vector control interventions in Nigeria, necessitated the establishment of mosquito surveillance sites in a few States in Nigeria. In order to make evidence-based-decisions, predictive studies using available data becomes imperative. We therefore predict the distribution of the major members of the Anopheles gambiae s.l. in Nigeria. Immature stages of Anopheles were collected from 72 study locations which span throughout the year 2020 resulted in the identification of over 60,000 Anopheline mosquitoes. Of these, 716 breeding sites were identified with the presence of one or more vector species from the An. gambiae complex and were subsequently used for modelling the potential geographical distribution of these important malaria vectors. Maximum Entropy (MaxEnt) distribution modeling was used to predict their potentially suitable vector habitats across Nigeria. A total of 23 environmental variables (19 bioclimatic and four topographic) were used in the model resulting in maps of the potential geographical distribution of three dominant vector species under current climatic conditions. Members of the An. gambiae complex dominated the collections (98%) with Anopheles stephensi, Anopheles coustani, Anopheles funestus, Anopheles moucheti, Anopheles nilli also present. An almost equal distribution of the two efficient vectors of malaria, An. gambiae and Anopheles coluzzii, were observed across the 12 states included in the survey. Anopheles gambiae and Anopheles coluzzii had almost equal, well distributed habitat suitability patterns with the latter having a slight range expansion. However, the central part of Nigeria (Abuja) and some highly elevated areas (Jos) in the savannah appear not suitable for the proliferation of these species. The most suitable habitat for Anopheles arabiensis was mainly in the South-west and North-east. The results of this study provide a baseline allowing decision makers to monitor the distribution of these species and establish a management plan for future national mosquito surveillance and control programs in Nigeria.
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    Molecular characterization and Plasmodium falciparum transmission risks of Anopheles mosquitoes in Malete, Nigeria
    (2023) Abiodun Obembe
    ABSTRACT. Introduction: Studies on malaria vector surveillance are useful for evidence-based control in specific communities. Such studies are lacking in Malete, a rapidly growing peri-urban community in Nigeria. Objective: To assess sibling species identity, human blood indices, and Plasmodium falciparum transmission risks by Anopheles mosquitoes, in Malete. Methods: I collected endophilic mosquitoes quarterly from inhabited houses using the pyrethrum spray catch technique. I identified the mosquitoes, and probed for the presence of human blood and P. falciparum, using standard PCR and ELISA methods, respectively. Results: Anopheles mosquitoes (90%) were the most abundant compared to Culex (10%) and Mansonia (0,5%). Specifically, A. gambiae (85%) were predominant over A. coluzzii (11%) and A. arabiensis (3%). The Anopheles sibling species had generally high human blood indices (≥0,82). However, A. gambiae man-biting rates (0,92-3,64) were higher than A. coluzzii (0-0,84) and A. arabiensis (0-0,27). Plasmodium falciparum sporozoite infection (3%) was found only in A. gambiae. Conclusion: While P. falciparum infection was 3%, long-lasting insecticidal nets should be deployed for control in Malete, particularly of A. gambiae.
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