Animal Waste, Water Quality and Human Health

46Animal Waste, Water Quality and Human Healthflagellum, adhesins, and toxins are thought to play a role in colonization, invasion ofepithelial cells, and in activation or evasion of the host innate and acquired immunesystem (Crushell et al. 2004, Young et al. 2007, Zilbauer et al. 2008). However,many of these possible virulence factors appear to be widely distributed amongCampy. jejuni strains (Zhang et al. 2010).Campy. jejuni can be isolated from the faeces of a large number of wild anddomestic animal species. In most animal species, the organism appears to be acommensal in the gastrointestinal tract and clinical disease is not commonlyobserved (Altekruse et al. 1994, Silva et al. 2011). There is a high prevalence ofCampylobacter colonization among birds and their intestines are thought to beideal incubators for the organism.While most Campylobacter infections are sporadic, outbreaks of illness havebeen associated with the consumption of contaminated raw beef liver, raw milkand untreated drinking-water (Robinson 1981, Garg et al. 2006, Hara-Kudo &Takatori 2011). Experimental infections in humans have shown the infectiousdose to be as low as 500 organisms (Black et al. 1988). This value is close to anestimated 360 organisms that were consumed in a raw beef liver-associatedoutbreak in Japan (Hara-Kudo & Takatori 2011). The reason for the sporadicnature of most Campylobacter infections is unknown; however, it may beexplained by variable levels of exposure coupled with differences insusceptibility in the human population and/or differences in virulence amongCampy. jejuni strains.Campy. jejuni can also be readily isolated from retail poultry and case-controlstudies have established that consumption and/or handling of undercooked poultryis the most significant risk factor for human campylobacteriosis (Mead et al.1999,Friedman et al. 2004). Further, recent studies which have compared the genotypesof C. jejuni isolated from human, animal and environmental sources using multiplelocus sequence typing (MLST) have also concluded that chickens are the mostimportant source of human infections (Lévesque et al. 2008, Sheppard et al.2009, Oporto et al. 2011). Interestingly, these MLST studies have also shownthat ruminants are an important secondary source of the organism. Cattle andsheep are known to shed the organism in their faeces and it can be readilyisolated from liver and offal samples; however, its prevalence rate in retail beefand mutton is relatively low compared with rates in raw poultry (Kramer et al.2000, Wong et al. 2007, Ogden et al. 2009). The route of infection fromruminant sources, therefore, likely includes consumption of raw milk (Teuniset al.2005), animal contact and drinking untreated water (Belongia et al. 2003,Friedman et al. 2004, Humphrey et al. 2007).Green et al. (2006) in Manitoba, Canada, first reported that young children (