Animal Waste, Water Quality and Human Health

Zoonotic waterborne pathogen loads in livestock 83Smith 1997). Lambs appear to shed fewer oocysts (Crypto. parvum notDNA-confirmed) if they ingest oocysts at two months of age compared to beinginfected at six days of age; mean peak oocyst shedding was 2.5 × 10 7 versus2.2 × 10 9 , respectively (Ortega-Mora & Wright 1994).Faecal shedding of Cryptosporidium parvum among swine, chickens, geese andducks is infrequent and typically not a significant environmental source of thisspecies of protozoa (Hunter & Thompson 2005, Xiao & Fayer 2008). Similarly,most cross-sectional surveys conducted to date have found a moderately lowprevalence of Cryptosporidium spp. in adult horses, with some reportsindicating higher infections occurring in foals. For example, a survey on trailhorses utilising public trails in Colorado, USA, found that 0.3% had detectableconcentrations of Cryptosporidium spp. (Forde et al. 1997). Among the generalequine population, two surveys detected Cryptosporidium in 27% (21/77) ofnormal foals and 29% (83/285) of diarrhoeic foals (Coleman et al. 1989,Browning et al. 1991). In a two-year survey by Coleman et al. (1989), 15%(8/55) of pasture-reared foals were found to be infected with Cryptosporidiumthe first year, but the subsequent year foals were negative. Cryptosporidium wasdetected in 15 to 31% of foals, 0 to 5% of weanlings and 0% of yearlings andmares (Xiao & Herd, 1994a). Cole et al. (1998) determined that 7% (5/70) offoals on breeding farms and 0.3% (1/366) of geldings, intact males and mareswere infected with Cryptosporidium. Among horses used as packstock in themountains of California, USA, none of 305 animals had detectable levels ofCryptosporidium (Atwill et al. 2000). About 3.5% of horses in Poland werefound to shed low numbers of Cryptosporidium parvum oocysts (Majewskaet al. 2004).3.2.2 Giardia duodenalisGiardia duodenalis like Crypto. parvum infects the intestinal tract of a wide rangeof hosts, including humans, dogs, cats, cattle, sheep, horses, rodents and a varietyof other wild mammals. This species of Giardia is further divided into subgroupsreferred to as Assemblages A through G (see Chapter 2). Assemblage A infectshumans and other primates, livestock, companion animals, rodents and othermammals; Assemblage B infects humans, other primates and dogs; assemblagesC and D infect dogs; Assemblage E infects cattle and other hoofed livestock;Assemblage F infects cats; and Assemblage G infects rats (Hunter andThompson 2005). Of particular concern for agricultural watersheds isAssemblage A because this type of Giardia is infective to humans and is alsoshed by livestock, dogs and cats, humans, and certain wildlife species.