Geospatial seasonal environmental impacts on the distribution and abundance of <i>Schistosoma haematobium</i> vectors in two districts of the Ase River Catchment, Delta State, Nigeria

Abstract

Snails of the genus, Bulinus are known to transmit urinary schistosomiasis. Longitudinal limnological and Bulinus surveys were geospatially performed at 11 study sites frequently visited by humans for 24 months using APHA and scooping/hand-picking techniques in the Ase River, Delta State. The collected snails were subsequently identified, counted, and recorded. The results of the physicochemical parameters [water temperature (0C), Total Dissolved Solids (TDS), Electrical Conductivity (EC), pH, Dissolved Oxygen (DO), and Biochemical Oxygen Demand (BOD)] showed monthly and study site variations. All physicochemical parameters analyzed were significantly different (P<0.05) in both years except air temperature (P > 0.05). A total of 2,345 Bulinus species were collected, with year A (1,101) and year B (1,244) having their highest Relative Abundance (R.A) of 17.17% and 16.80% in July. The interannual Bulinus R.A was not significant (p = 0.9990; F = 1.49x10-006, df = 1). However, the monthly R.A was significantly different (F = 22.99, df =11) and accounted for 95.83% of the total variance. Bulinus R.A varied within and between years, with lower abundance in the dry season. Lagos-Iyede, Iyede-Ame, Onogboko, and Itobi-Ige study sites had the highest Bulinus R.A in both years with no significant difference (P < 0.0001; F = 0.2015, df = 10). Nevertheless, the monthly abundance was significantly different (F = 73.84, df = 11). This study identified Bulinus truncatus, B. globosus, and B. senegalensis and B. globosus had the highest (47.98%) R.A, followed by B. truncatus(37.06%) and B. senegalensis (14.99%). Geospatially, B. truncatus, B. globosus, and B. senegalensis R.A peaked at Iyede-Ame with 15.30%, 16.80%, and 27.64% respectively and the difference was significant (F = 12.46, df = 10). In year A, Principal Component Analysis revealed that B. truncatus had a strong association with DO and BOD, while B. globosus and B. senegalensis correlated positively with water temperature, TDS,  EC, and pH. Comparatively, B. globosus R.A was strongly influenced by EC and TDS in the year B. TDS and EC exhibited a strong association.