Animal Waste, Water Quality and Human Health

160Animal Waste, Water Quality and Human Healthanalysed the factors contributing to variation in microbial risks associated with thesesources. Even when the source matrix is perceived to be the same (for example, cattlefaeces) the actual risk will vary dependent on specific pathogen prevalence, sheddingconcentrations, geographic, animal diet, seasonal and temporal distributions,availability of hosts and treatment and mitigation measures. Quantification ofmicrobial sources (particularly prevalence and concentration) and the extent oftheir variability is necessary for constructing predictive models of microbialloads within catchments. It is also essential for the cost-effective prioritisationof catchment management actions. The following information summarises ananalysis of the existing data on prevalence and concentrations of Escherichiacoli, Cryptosporidium oocysts and Giardia cysts as indices of microbial riskarising from wildlife and livestock in drinking-water catchments.A global review of the literature published up to 2005 was conducted to determinethe extent of variationinreported concentrationsof prevalenceandpathogen sheddingintensities in animal faeces. Data from each study were pooled and analysed by animaltype and where possible by geographic location for Europe/United Kingdom,Australasia and North America. The majority of studies examined prevalence ofpathogens in animal faecal matrices with fewer studies reporting pathogenconcentrations excreted by animals. Although domestic livestock such as cattleand sheep have been frequently tested for the prevalence of Cryptosporidium (n= 23 and n = 12, respectively), fewer studies have tested samples from wildlife (n= 1 for some species). Also, different studies had widely different numbers ofsamples analysed. For example, estimates of Cryptosporidium oocyst prevalence inadult cattle were derived from between 19 and 8064 individual samplesdepending on the study, and hence data need to be interpreted with caution.Ranked by mean prevalence, Cryptosporidium oocysts in animal faeces scoredhighest in juvenile sheep faeces, adult sheep faeces, juvenile cattle and pig faeces,respectively (see Table 5.1). The mean prevalence of Cryptosporidium in adultcattle faecal material was less than expected (ranking 11 th ), below that ofkangaroos and goats. The prevalence of Cryptosporidium oocysts in animalfaeces is presented graphically in Figure 5.2.Table 5.1Mean prevalence rates of Cryptosporidium oocysts in animal faeces.Ranking Animal Age n* Mean prevalence Median prevalence1 Sheep juvenile 5 0.524 0.7102 Sheep adult 7 0.346 0.2703 Cattle juvenile 23 0.283 0.210(Continued)