Human Contamination and Schistosome Infection Intensity in Bulinid and Planorbid Snail Vectors in Kadawa Irrigation Area, Kano State, Nigeria

Abstract

Objectives of the Study: An Epidemiological Research, a cross-sectional study, was conducted to determine the magnitude of human contamination of irrigation canal perimeter as it relates to the prevalence and intensity of schistosome cercarial infection in snail vectors. Place and Duration of Study: The study was conducted along water canal located within an irrigation area, Kano River Project Phase I, Kadawa, between January and June, 2012. Methodology: The study area was categorized into Zone of Heavy Contamination (ZHC), Zone of Light Contamination (ZLC) and Zone of Free Contamination (ZFC) based on the density of faecal lumps observed along the canal perimeter using 1 m2 quadrat sampling technique. Snail vectors of schistosomiasis were collected from these zones, identified and subjected to cercarial shedding. Brevifurcate apharyngeate cercariae were identified as schistosome cercariae. Results: Of the 827 snails collected 28.54% shed schistosome cercariae. The breakdown of infection prevalence was 31.37%, 27.69% and 26.26% for ZHC, ZLC and ZFC respectively. Three snail species recovered in the study area, Bulinus globosus, B. rohlfsi and Biomphalaria pfeifferi had infection intensity of 8.6, 5.67 and 3.94 respectively, with total mean intensity of 4.67. A Chi-squared analysis did not show any significant difference in infection prevalence in the three zones (χ2cal. 0.025, χ22, 0.05 = 5.99). However, infection intensity was significantly different in the three zones and among the three snail species using analysis of variance (P<0.05). Conclusion: Human environmental contamination with faeces and urine around irrigation canals remains the source of infection to snail hosts and then to humans. It is presumed that contact control through avoidance of defaecation in the open and building of pit latrines near water contact points along irrigation canals will be effective means of drawing a barrier to infection with schistosomes in the study area.