Abstract:
Malaria transmission in urban areas of sub-Saharan Africa, though currently negligible (scarcely above 10%), is an increasing phenomenon. Factors which support the prevalence of malaria in urban areas are mainly anthropogenic activities that promote continuous presence and breeding of Anopheles mosquitoes. Although increasing surface water pollution caused by rapid urbanization was believed to have hampered the development of Anopheles larvae in general; eliminated certain species like Anopheles funestus; other species such as Anopheles gambiae complex have become well adapted to organically polluted water bodies. This study examined environmental factors that influenced the presence and population of Anopheles mosquito larvae in Accra Metropolitan Area (AMA) and Sekondi-Takoradi Metropolitan Area (STMA) of Ghana. It also sought to examine how climate variability may influence the presence of Anopheles mosquitoes in the future under climate change scenarios. Using geographic information science-based techniques, 21 randomly selected points were studied between March 2013 and February 2014. Aquatic habitats of Anopheles mosquito larvae were identified and from selected points in each habitat, larvae and water were sampled. The larvae were reared to maturity, identified morphologically and further characterized using molecular methods. Thirty (30) physical, chemical and biological variables of water sampled were also measured and their association with Anopheles larval presence and population were determined. Thirty-three (33) years of rainfall and temperature data for the two cities were acquired from Ghana Meteorological Agency (GMET) from which projections for rainfall and temperature were predicted for the next 35 years (2050). The results showed that almost all (>99%) of the larvae sampled were from the Anopheles gambiae complex. Results revealed that 62% of the Anopheles gambiae complex were An. coluzzii and 29% were An.
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gambiae s.s. Sixty-six percent of the Anopheles breeding habitats in both cities were classified as permanent and 74.5% were man-made. Logistic regression and negative binomial models applied revealed that various environmental factors had statistically significant influence on the presence and population of Anopheles mosquitoes. Some of these variables included depth of water [OR= 0.9868, SE= 0.0053; p= 0.014], substratum (Others) [OR= 0.0993, SE= 0.1062; p= 0.031], water temperature [OR= 1.1278, SE= 0.0614; p= 0.027], atmospheric temperature [OR= 1.2196, SE= 0.1139; p= 0.033], EC [OR=0.9999, SE= 0.0001; p= 0.033], sodium [OR= 1.0042, SE= 0.0021; p= 0.044], water beetle [OR= 2.4211, SE= 1.0600; p= 0.043], dragonfly [OR= 6.5602, SE= 5.1498; p=0.017] and tadpole [OR= 2.6364, SE= 0.9668; p= 0.008] for logistic regression. In hierarchical models, other variables had statistically significant association with the presence and population of Anopheles mosquitoes. When projected, the duration of the minor rainy season will be extended from August to December instead of the current September and October. Increase in atmospheric temperature will most likely lead to Anopheles larval density hence an increase in the population of the malaria vectors in the two cities. Put together the data showed that degradation of the environment through human activities and environment variability will increasingly favour the presence and propagation of Anopheles mosquitoes, and increase in malaria transmission rates in the cities, if no intervention strategies are adopted.