Pathogen Pathways − Contamination of water bodies via artificial drainage
1. Introduction and background
The numbers of reported cases of gastroenteritis in New Zealand (Table 1) are the highest among developed countries (Orchard et al. 2000). The uniquely high prevalence of notified out-breaks of Campylobacteriosis and Giardiasis are more frequent in rural regions, highly stocked with sheep, beef and dairy cattle.
Table 1: Reported cases of enteric diseases 1997
| Enteric Disease | NZ | Aust | USA | Can | UK |
|---|---|---|---|---|---|
| Reported cases per 100 000 population | |||||
| Campylobacteriosis | 244.5 | 96.7 | NR | 44.7 | 100.5 |
| Cryptosporidiosis | 9.9 | NR | 1.1 | NR | 8.7 |
| Giardiasis | 68.6 | NR | NR | 18.7 | 10.6 |
| Listeriosis | 1.0 | 0.4 | NR | 0.2 | 0.2 |
| Salmonellosis | 32.2 | 37.8 | 15.7 | 65.3 | 6.5 |
| Shigellosis | 3.4 | 6.5 | 8.6 | 4.0 | 4.0 |
| VTEC/STEC | 0.4 | NR | 1.0 | 2.1 | 2.1 |
| Yersiniosis | 13.3 | 2 | NR | 0.3 | 0.3 |
NR= not recorded
Source: Orchard et al. 2000
Hearnden et al. (1998) reviewed indirect evidence that rural outbreaks of Campylobacteriosis and Giardiasis are associated with periods of direct contact with animal faeces (for example, lambing assistance) and/or contamination of town water supplies with animal faeces (for example, agricultural runoff during storm events). New Zealand dairy cattle are a large reservoir of Campylobacter jejuni, Cryptosporidium and Giardia. The spread of these pathogens to amenity or potable waters via discharge of surface runoff, or subsurface drainage, from grazed areas, pose recognisable risks to the health of humans and livestock (Hearnden et al. 1998; Brown et al., 1998).
Two thermophilic Campylobacter subspecies, C. jejuni and C. Coli, are responsible for almost all human cases of Campylobacteriosis. Campylobacter have a low infectious dose: less than 1000 organisms ingested have been reported to cause enteritis in people (Reid, 1991). Campylobacter jejuni is the principle bacterial hazard for recreational water users or those drinking untreated water, and this subspecies has been identified in waters exiting mole and pipe systems draining paddocks receiving high rates of dairy shed effluent (Ross and Donnison, 2003).
Cryptosporidium and Giardia are both “Priority 1” determinants along with faecal coliforms in Drinking Water Standards for New Zealand 1995. They are protozoa, not bacteria and, therefore, do not respond to the normal anti-bacterial treatment systems, both having very resistant oocysts or cysts. Both of these organisms cause serious gastro-enteric conditions in humans that are responsible for many lost workdays. For some immune-compromised patients infection by Cryptosporidium can be fatal. Cattle infected with Cryptosporidium develop scours and significant weight loss can result.
To date, research on linkages between Campylobacteriosis epidemiology, environmental characteristics, and microbial pathogen impacts on water quality has been conducted at the regional scale or larger (Hearnden et al. 1998). There has been little research into the relationships between occurrence of Campylobacter, Giardia and Cryptosporidia in host dairy cattle, other potential hosts and transport vectors, and survival of pathogenic microorganisms in the agroecosystems associated with dairy farms.
Recent research at Massey University’s No. 4 Dairy Farm has shown that the prevalence of Campylobacter spp. varied between 52 percent in dry cows to 15 percent at calving in the 1999/2000 season (Wu, 2001). Previous single point-in-time surveys indicated prevalence of 54 percent in dairy cattle on the same farm (Ahmed, 1999). A survey of Giardia prevalence in Waikato dairy calves also shows temporal variability with the greatest incidence occurring in young calves (Hunt et al., 2000).
The series of research objectives covered in this report aim to quantify the relative importance of drainage water, exiting artificial mole and pipe systems, and surface runoff from grazed dairy pasture as pathogen transmission routes to surface-water bodies. The experiments described in this report will try to accommodate the temporal variability in the prevalence of pathogens in dairy cow faeces by measuring the transmission of pathogens from simulated field drainage events where fresh dung patches are spiked with laboratory cultured Campylobacter as well as measurements made during normal grazing and drainage events where the prevalence and source are uncertain.
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