Malacological Survey of Schistosomiasis and Fecal Contamination of Public Water Sources Within Informal Settlements of Kisumu City, Kenya

Abstract

Human schistosomiasis and soil-transmitted helminthiases (STHs) remain a major public health problem, responsible for significant morbidity and mortality in developing countries, despite availability of effective, safe and cheap drugs for their treatment. Long-term prevention of schistosomiasis and STHs has been difficult to i: achieve due to persisting conditions of poverty, lack of access to clean water, ,,.» occupational hazards and poor sanitation. A number of research studies have ~I CJ) previously been conducted towards control interventions to ameliorate human G') m suffering from these infections. However, most of the research has focused mainly on • Z controlling of the infections in human populations without considering other targets en 0 within the parasite's life cycle that can also aid in disruption of transmission. This • 1"" study was, therefore, carried out to determine the distribution and prevalence of -I Z,."'. schistosome infection in intermediate snail vectors, and fecal contamination of public CDwater sources within the informal settlements of Kisumu city, Kenya. Lake Victoria, ;:c ~ in Kisumu city is known to be the main source of schistosomiasis in this region, ~;o whereas overcrowding and lack of adequate clean water and sanitation within the ~ 00_ informal settlements promote STH infections. Water sources were mapped using a --- Geographical Information System (GIS). Snails were sampled from 81 selected points -« that had human-water contact activities (25 along the lakeshore and 56 from inland -_<_ habitats), and transported to the laboratory where they were identified to species level, based on shell morphology and screened for infection. To determine fecal contamination among water sources, the membrane filtration technique was used for enumeration of total and fecal coliform bacteria (Escherichia coli) in water samples collected from dams, rivers, springs and wells. Statistical analyses were performed using SAS version 9.2 and a P < 0.05 was. considered significant. ANOVA and Fisher's exact tests were used to compare differences between variables. Out of 1,059 snails collected, 407 (38.4%) were identified as Biomphalaria sudanica, 425 (40.1%) as Biomphalaria pfeifJeri and 227 (21.5%) as Bulinus globosus. The log-transformed mean snail abundance varied significantly across the 6 informal areas (F5, 75 = 4.93, P = 0.0006), with Nyamasaria recording the highest abundance. Overall, 19 (1.8%) of the snails collected shed schistosome cercariae. The infection prevalence in Bulinus spp. (3.9%) versus Biomphalaria spp. (1.9%) was comparable (P = 0.0843). Only water temperature had positive association with snail abundance (rs = 0.3, n = 81, P = 0.0195). Out of the 80 water sources sampled, 76 (95%) were highly contaminated with fecal matter The difference in the log-transformed mean fecal coliform density among the informal areas was not significant, indicating similar levels of fecal contamination across the board (F6,68 = 1.46, P = 0.2043). There was a significant negative association between lateral distance from pit latrines and fecal coliform density for wells (rs = - 0.34, n = 53, P = 0.0142). The high abundance of Biomphalaria and Bulinus spp. as well as observation of field-caught snails shedding cercariae confirmed that besides Lake Victoria, the local risk for schistosomiasis transmission exists within the informal areas of Kisumu city. Schistosomiasis control interventions in these areas need to incorporate focal snail control to complement chemotherapy. Treatment of public water sources and improvements in local sanitation and hygiene as well as public health awareness are advocated for in such urban settings. Future studies may benefit from use of more sensitive molecular techniques like peR for snail identification.