Animal Waste, Water Quality and Human Health

Assessing the importance of zoonotic waterborne pathogens 35meters from the site of release from the snail. Types of bodies of water that may becontaminated include: open wells, springs, streams, irrigation canals and otherhydraulic structures in irrigation schemes, rivers, impoundments, reservoirs andlakes. Risky behaviours that predispose individuals to schistosome infectioninclude the use of bath and laundry water from a contaminated source, crossingaffected streams, irrigation canals and rivers, agricultural activities, and fishingand swimming in infested rivers. It should be stressed that in addition to theserisks of infection, there are also behaviours of schistosome-infected individualsthat put others at risk such as urinating and/or defecating in fields, in or nearwater bodies, and lack of proper sanitation in general.The disease is characterized by an acute phase usually occurring 2–12 weeksafter cercarial skin penetration followed by the development of debilitatingdisease which can persist for years if left untreated. Symptoms includeinflammatory and granulomatous reactions around the sites where eggs aredeposited in the host’s tissues. The most commonly affected organs are theliver and intestines (by S. mansoni, S. japonicum and S. mekongi) and thegenito-urinary tract (by S. haematobium).Among the four species, S. japonicum is unique because it is the only species inwhich zoonotic transmission is considered important. In the People’s Republic ofChina and in the Philippines, around 60 million individuals are at risk and anestimated one million people are infected (Blas et al. 2004, Zhou et al. 2007).While a small focus of transmission persists on the island of Sulawesi inIndonesia (Izhar et al. 2002), the disease has been eliminated in Japan (Tanaka& Tsuji 1997). Humans and animals are a significant sources of these parasites.Animals that contribute significantly to the transmission cycle include cattle,water buffalo, pigs, goats, dogs and wild rats (Mao 1948; Lung et al. 1958,Maegraith 1958, Pesigan et al. 1958, Dumag et al. 1981, Fernandez et al. 1982,Zheng et al. 1989, Wu et al. 1992, Chen 1993, Brindley et al. 1995, Wan et al.1998, McGarvey et al. 1999). Infections are transmitted naturally betweenman and animals with the infection being maintained by all of these species(Nelson 1975). Prevalence studies in animals have shown that cattle and buffaloare the most commonly infected animals in China. This finding is supported bystudies on the spatial distribution of animal faeces in endemic areas of Chinashowing that cattle dung contributes substantially to the transmission of S.japonicum in that country. While equivalent studies have not been done in thePhilippines, studies do provide indications of the relative contribution of specificanimals to S. japonicum transmission (Carabin et al. 2005). For example,Table 2.3 below presents a summary of findings from a study based on surveysin 50 barangays (villages) in Dagami, Leyte, the Philippines in 1979 (Dumaget al. 1981).