New hydroepidemiological models of indicator organisms and zoonotic pathogens in agricultural watersheds |
| |
Authors: | Graham B. McBride Steven C. Chapra |
| |
Affiliation: | a National Institute of Water and Atmospheric Research (NIWA), P.O. Box 11-115, Gate 10, Silverdale Road, Hamilton, Waikato 3216, New Zealand b Department of Civil and Environmental Engineering, Tufts University, Medford, MA 02155, USA |
| |
Abstract: | Simple analytical models are derived to assess how a series of cattle animal farms affect the transport and fate of an indicator organism (Escherichia coli) and a zoonotic pathogen (Campylobacter) in a stream. Separate steady-state mass-balance models are developed and solved for the ultimate minimum and maximum concentrations for the two organisms. The E. coli model assumes that the organism is ubiquitous and abundant in the animals’ digestive tracts. In contrast, a simple dose-response model is employed to relate the Campylobacter prevalence to drinking water drawn from the stream. Because faecal indicators are commonly employed to assess the efficacy of best management practice (BMP) interventions, we also employ the models to assess how BMPs impact pathogen levels. The model provides predictions of (a) the relative removal efficacy for Campylobacter and (b) the prevalence of Campylobacter infection among farm animals after implementation of BMPs. Dimensionless numbers and simple graphs are developed to assess how prevalence is influenced by a number of factors including animal density and farm spacing. A significant outcome of this model development is that the numerous dimensional input and parameter variables are reduced to a group of just four dimensionless Campylobacter-related quantities, characterizing: animal density; in-stream attenuation; animal-to-animal transmission; and infection recovery. Calculations reveal that for some constellations of these four quantities there can be a greater-than-expected benefit in that the proportional reduction of stream Campylobacter concentrations post-BMP can substantially exceed the proportional reduction of concentrations of E. coli in that stream. In addition, a criterion for system sterility (i.e., the conditions required for the farm infection rate to decrease with downstream distance) is derived. |
| |
Keywords: | Campylobacter E. coli Faecal indicators Waterborne pathogens Best management practices Hydroepidemiology Stream River |
本文献已被 ScienceDirect 等数据库收录! |
|