Entomological surveillance reveals transmission of malaria but not lymphatic filariasis in two communities in North-West Nigeria.

Malaria and lymphatic filariasis (LF) are two serious public health challenges in sub-Saharan Africa, and both diseases are transmitted by Anopheles mosquitoes. Successful control of both diseases requires detailed information on transmission dynamics; thus, this study investigated malaria and LF transmission indices in two (2) communities (Jidawa and Kargo) in North-West Nigeria. Anopheles mosquitoes were sampled from twenty-five (25) randomly selected houses from each of the two communities using pyrethrum spray collection (PSC). The samples were identified morphologically and molecularly characterised using polymerase chain reaction (PCR). Human biting rate (HBR), indoor resting density (IRD), sporozoite rate (SR) and entomological inoculation rate (EIR) were calculated using standard formulae. The thorax region of the collected samples were dissected and smeared; then, Plasmodium and Wuchereria bancrofti parasites were identified using microscopy. A total of 2417 Anopheles mosquitoes were collected, and all were identified morphologically as An. gambiae s.l. Further molecular identification of sibling species revealed that An. gambiae and An. arabiensis were the only sibling species present. A total of 818 Anopheles mosquitoes were screened for Plasmodium and Wuchereria bancrofti parasites. A total of 180 samples were positive for Plasmodium parasites (Jidawa = 151; Kargo = 29), and none was positive for W. bancrofti (0%). Result of entomological indices for malaria transmission showed that indoor resting density was higher in Jidawa (10 mosquitoes/room/night) while human biting rate (2.07 bites/person/night), sporozoite rate (29.3%) and entomological inoculation rate (0.61) were higher in Kargo. In total, 35.2% of the samples were blood-fed while 67.4% were parous. There is active transmission of malaria in the two communities but not LF, suggesting the effectiveness of mass drug administration for LF. Concerted efforts should be focused on malaria control as transmission of the disease persists.

Spatial distribution and ecological niche modeling of geographical spread of Anopheles gambiae complex in Nigeria using real time data.

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.

High pyrethroid-resistance intensity in Culex quinquefasciatus (Say) (Diptera: Culicidae) populations from Jigawa, North-West, Nigeria.

This study examined pyrethroid resistance intensity and mechanisms in Culex quinquefasciatus (Say) (Diptera: Culicidae) populations from Jigawa, North-West Nigeria. Resistance statuses to permethrin, lambda-cyhalothrin and alphacypermethrin were determined with both WHO and CDC resistance bioassays. Synergist assay was conducted by pre-exposing the populations to Piperonyl butoxide (PBO) using the WHO method. Resistance intensities to 2x, 5x and 10x of diagnostic concentrations were determined with the CDC bottle method. Species analysis and presence of knockdown mutation (Leu-Phe) were done using Polymerase Chain Reaction (PCR). Results showed that Cx. quinquefasciatus was the only Culex spp. present and "Kdr-west" mutation was not detected in all analyzed samples. Using WHO method, Cx. quinquefasciatus resistance to permethrin was detected in Dutse (12.2%) and Kafin-Hausa (77.78%). Lambda-cyhalothrin resistance was recorded only in Kafin-Hausa (83.95%) with resistance suspected in Ringim (90%). Resistance to alphacypermethrin was recorded in all locations. Pre-exposure to PBO led to 100% mortality to alphacypermethrin and lambda-cyhalothrin in Ringim while mortality to permethrin and alphacypermethrin in Dutse increased from 12.2% to 97.5% and 64.37% to 79.52% respectively. Using CDC bottle bioassay, resistance was also recorded in all populations and the result shows a significant positive correlation (R2 = 0.728, p = 0.026) with the result from the WHO bioassay. Results of resistance intensity revealed a very high level of resistance in Kafin-Hausa with susceptibility to lambda-cyhalothrin and alphacypermethrin not achieved at 10x of diagnostic doses. Resistance intensity was also high in Dutse with susceptibility to all insecticides not achieved at 5x of diagnostic doses. Widespread and high intensity of resistance in Cx. quinquefasciatus from North-West Nigeria is a major threat to the control of diseases transmitted by Culex and other mosquito species. It is a challenge that needs to be adequately addressed so as to prevent the failure of pyrethroid-based vector control tools.