A prevalence study of mosquitoes in Lagos metropolis

Ajala, Abigail Ayodele (2016)



The study investigated the prevalent genera of mosquitoes in Lagos metropolis based on the characteristic morphology of their larvae. It also determined the likely possible variations in prevalence of mosquito larvae in different localities of the study area, and likely seasonal variation in prevalence. Mosquito larvae were collected partly during the rainy season (August and September,2015) and partly in the dry season, (November and December, 2015) from seventeen (17) Local Government Areas (LGAs) of Lagos within the metropolis (core Lagos). These areOjo,AmuwoOdofin, Apapa, Ajeromi/Ifelodun, Mainland, Surulere, Lagos Island, Mushin, Oshodi, Isolo, Shomolu, Kosofe, Alimosho, Ikeja, Agege, Eti-osa and IfakiIjaye. Five potential breeding sites in the LGAs, namely gutters, discarded tyres, discarded containers, household containers, and abandoned concrete electric poles were identified in both seasons.The collection of mosquito larvae was done using dipper and Pasteur pipette.Mosquito larvae were identified at the Department of Medical Microbiology and Parasitology,Lagos State University Teaching Hospital (LASUTH). Mosquito larvacollected werepoured into Petri dish for counting. The larvae were then poured into glass bottle and heated for five minutes to kill them. The larvae were further dehydrated in increasing concentration of ethanol (20%, 40%, 60%, 80% and absolute) for twenty minutes per concentration. They were cleared in xylene, and mounted in DistrenePlasticer Xylene (D.P.X.) on a dry microscope slide, covered with cover slip. Thereafter, the slides were viewed under microscope with ×4 objective lens. Data collected were analyzed using One way analysis of variance (ANOVA),Repeated analysis of variance and Student t-test. Alpha level was set at P< 0.05 of significance. Out of a total of 340 breeding sites investigated, only 125 of them contained mosquito larvae. A total of 2380 mosquito larvae belonging to three genera were collected and identified. These were Aedes 1502(63.1%), Culex 869(36.5%) and Anopheles 9(0.4%).In both raining and dry seasons,Aedes were predominant in discarded tyres. Culexwerepredominant in both seasons in the gutters. In discarded containers, Aedes were predominant in both seasons. In abandoned concrete electric poles, Aedes were predominant in the rainy season while no mosquito larvawas observed in the poles in the dry season. In household containers in the rainy season, Culex were the most abundant but in the dry season Aedes was. FewAnopheles were observed in the gutters and discarded tyres. There was no statistically significant difference (P>0.05) in the larvae genera collected in different breeding sites in the raining and dry seasons. There was also no statisticallysignificant difference (P>0.05) in the larvae distribution in the LGAsin the rainy and dry seasons. The study concluded that Aedes werethe predominant mosquitoes in the study area followed by Culex. In view of the fact that a few number of Anopheles were encountered, there seems to be no justification for the high cases of malaria that is usually insinuated. Therefore diseases that may be emerging are those caused by the pathogens carried by the predominant two genera of mosquitoes.