Exploring the Diversity and Vectorial System of Anopheline Mosquitoes (Diptera: Culicidae) in Chosen Ecological Settings within Nasarawa State, Nigeria
Mosquitoes are notorious for their nuisance and their role in transmitting disease-causing pathogens to humans. This research aimed to assess the distribution, abundance, and diversity of mosquitoes in three specific eco-settings within Nasarawa State, Nigeria. Anopheles mosquitoes were collected using the Pyrethroid Spray Catch (PSC) and Centre for Disease Control (CDC) light trap techniques, and their morphological identification was conducted using established keys. The presence of knockdown resistance (Kdr) was determined following standard protocols, while meal preference was determined using the Enzyme Linked Immuno Sorbent Assay (ELISA). Additionally, collected mosquitoes were categorized based on physiological conditions, and the molecular forms of Anopheline species were identified using established methods.
Throughout the selected eco-settings in Nasarawa State, a total of six species of Anopheles mosquito vectors were encountered: Anopheles gambiae s.l, An. funestus, An. nili, An. coustani, An. rufipes, and An. pharoensis. The study, conducted from January to December 2017, yielded a total of 15,417 mosquito vectors. Among these, Anopheline mosquitoes constituted the majority, accounting for 64.09% of the total collection. Analysis revealed significant variations in the relative abundance and distribution of mosquito vectors across the studied eco-settings. The month of May 2017 recorded the highest number of mosquitoes captured (1,273; 12.88%). An. gambiae s.l. was the most dominant species encountered across the eco-settings during both seasons, comprising 41.89% of the total collection, followed by An. coustani (19.49%). Indoor collections of An. gambiae s.l. accounted for 68.21% of the total. The indoor resting densities were determined as 4.46, 3.99, and 3.65 mosquitoes per person per hour per night for sparse woodland, wooded grassland, and swampy grassland, respectively. The wet season accounted for 57.24% of the collected vectors.
Analysis of abdominal conditions revealed that 27.40% of the mosquitoes were half gravid, 26.08% were gravid, and 25.97% were freshly fed. The highest human biting rate (HBR) was recorded in May 2017, with rates of 18.30, 22.90, and 23.00 bites per person per hour for sparse woodland, wooded grassland, and swampy grassland, respectively. Molecular analyses showed that the S form of An. gambiae s.s constituted 64.47% of the collection, while 15.47% and 10.93% were the M form of An. colluzzi and An. arabiensis, respectively. The sporozoite rates, indicating the presence of malaria parasites, were 20.20% in swampy grassland, 13.20% in sparse woodland, and 12.80% in wooded grassland. In terms of knockdown resistance (Kdr), 19.02% of the vectors were resistant (RR), 31.66% were heterozygous susceptible (RS), and 50.51% were susceptible (SS) in the study area.
Blood meal source analyses revealed that 47.47% of the mosquitoes fed on humans, 30.54% on bovines, and 21.72% on goats across the study area. Specifically, An. gambiae s.s obtained 95.95% of its blood meal from humans, 45.07% from bovines, and 33.66% from goats. When considering single blood meal sources, 98.56% originated from humans, 44.44% from bovines, and 28.32% from goats. An. arabiensis obtained 1.44% of its blood meal from humans, 55.56% from bovines, and 71.67% from goats, indicating a mixed blood meal source. Moreover, An. arabiensis acquired blood meals from various combinations, including human/goat (24.30%), human/bovine (30.43%), human/bovine/goat (33.85%), and bovine/goats (54.55%).
Overall, this study revealed that Anopheles species were abundant and important vectors of malaria in Nigeria. The results indicate the presence of mosquito-borne disease vectors in the study area, with many of them influenced by human activities.