Animal Waste, Water Quality and Human Health

40Animal Waste, Water Quality and Human HealthE. coli O157:H7 is able to survive for longer periods in sediments than inflowing water. It is thought that biological agents such as bactivorous protozoadecrease free living or planktonic E. coli O157 numbers and biofilm formationin sediments increases its long-term survival (Wang & Doyle 1998; Ravva et al.2010). Despite this, large waterborne disease outbreaks have been associatedwith the organism. One of the largest of these occurred in Swaziland wherecattle manure was thought to be the source of more than 40,000 cases ofwaterborne infection with the organism (Effler et al. 2001). Another largewaterborne outbreak occurred in May of 2000 in Walkerton, Ontario, Canadawhen heavy rains lead to the contamination of a municipal well with cattlemanure (Garg et al. 2006). This event, coupled with a failure of the townchlorination system, led to 2500 cases of illness and seven deaths in this smallcommunity. In addition to the acute effects of infection with the organism suchas haemorrhagic colitis and HUS, residents of Walkteron have been shown tohave suffered from long-term sequelae following infection such as higher ratesof irritable bowel syndrome, hypertension, renal impairment and cardiovasculardisease (Clark et al. 2010). In the USA, 10 waterborne outbreaks associatedwith EHEC E. coli O157:H7 and O145:NM were reported between 1971–2006(Craun et al. 2010). In the Scotland, water consumed by vacationers wasreported to be associated with an E. coli O157:H7 outbreak (Licence et al.2001). In Ireland, a case control study pointed to a private well water source asbeing the cause of an E. coli O157 outbreak in a child care facility (Mannexet al. 2007). Most if not all E. coli O157:H7 outbreaks related to drinking-wateroccur with water derived from small systems such as private wells wherethere is no chlorination or there has been a chlorination failure (Craun et al.2010; Smith et al.2006). In a number of these outbreaks and in sporadic caseshigh resolution molecular typing methods such as pulsed-field gelelectrophoresis and comparative genomic fingerprinting (Laing et al. 2008) haveverified the close relationship between isolates from cattle, water and humansand provided very strong evidence for the waterborne transmission of E. coliO157 (Bruce et al. 2003, Effler et al. 2001, Mannix et al. 2007, Jokinen et al.2011).The prevalence of EHEC infections varies significantly from country tocountry and among regions within countries (20 cases per 100,000population members). While some of this difference can be attributed todifferences in surveillance and diagnostic abilities among countries, differencesin rates of infection also appear to be related to cattle density, the level of beefconsumption and cultural practises which promote consumption of uncooked orundercooked beef, e.g. HUS rates and beef consumption per capita in Argentinaare amongst the highest in the world (Rivas et al. 2008). Regional differences in