Effects of Combined Water Potential and Temperature Stresses on
            <i>Cryptosporidium parvum</i>
            Oocysts

Walker, Mark J.; Leddy, Katherine; Hager, Elaine C. H.

doi:10.1128/aem.68.4.2093a-2093a.2002

Cited by 9 publications

(11 citation statements)

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“…It is important, therefore, when modelling the fate of pathogens in the environment, that inactivation rates used are appropriate for temperatures for the climate in question. Previous studies have examined inactivation of Cryptosporidium at temperatures of up to 30°C (Walker et al. 2001; Jenkins et al.…”

Section: Discussionmentioning

confidence: 99%

“…Salt solutions ( ca 250 ml) containing 0·08 and 0·77 mol −1 NaCl were placed into the bottom of sealable airtight jars (capacity ca 2 l). According to the literature, these molal NaCl solutions produce and maintain simulated soil matric potentials of approximate field capacity and dry conditions respectively (wilting point) (Walker et al. 2001), and were designated ‘wet’ and ‘dry’ in this study.…”

Section: Preparation Of Soil Microcosmsmentioning

confidence: 99%

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Environmental inactivation of Cryptosporidium oocysts in catchment soils

et al. 2005

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Aims: To generate field-relevant inactivation rates for Cryptosporidium oocysts in soil that may serve as parameter values in models to predict the terrestrial fate and transport of oocysts in catchments. Methods and Results: The inactivation of Cryptosporidium oocysts in closed soil microcosms over time was monitored using fluorescence in situ hybridization (FISH) as an estimate of oocyst 'viability'. Inactivation rates for Cryptosporidium in two soils were determined under a range of temperature, moisture and biotic status regimes. Temperature and soil type emerged as significantly influential factors (P < 0AE05) for Cryptosporidium inactivation. In particular, temperatures as high as 35°C may result in enhanced inactivation. Conclusions: When modelling the fate of Cryptosporidium oocysts in catchment soils, the use of inactivation rates that are appropriate for the specific catchment climate and soil types is essential. FISH was considered cost-effective and appropriate for determining oocyst inactivation rates in soil. Significance and Impact of the Study: Previous models for predicting the fate of pathogens in catchments have either made nonvalidated assumptions regarding inactivation of Cryptosporidium in the terrestrial environment or have not considered it at all. Field-relevant inactivation data are presented, with significant implications for the management of catchments in warm temperate and tropical environments.

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Section: Discussionmentioning

confidence: 99%

Section: Preparation Of Soil Microcosmsmentioning

confidence: 99%

Environmental inactivation of Cryptosporidium oocysts in catchment soils

et al. 2005

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“…Interestingly,this earlier study found a sixfold higher prevalence of C. parvum in fecal samples collected per rectum from the adult cattle (1.1%) compared with the very low prevalence of C. parvum (0.18%) in fecal pats collected off the ground from the same herds on the same day. This suggests that once fecal material is deposited in the environment, C. parvum oocysts are subjected to one or more environmental stressors (e.g., thermal) that function to reduce the effective environmental load of this protozoal parasite (Walker et al, 2001). For example, we have shown that seasonal temperature fluctuations common to California's agricultural regions induce rapid inactivation via premature excystation of C. parvum oocysts once the daily maximum air temperature exceeds 25°C (Li et al, 2005).…”

Section: Resultsmentioning

confidence: 99%

Environmental Load ofCryptosporidium parvumOocysts from Cattle Manure in Feedlots from the Central and Western United States

et al. 2006

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The first step in assessing the risk of water contamination by Cryptosporidium parvum oocysts from feedlot cattle (Bos taurus) production systems is to quantify the number of C. parvum oocysts present in the fecal material deposited by feedlot cattle. Our primary objective for this project was to estimate the daily environmental load of C. parvum oocysts in fecal material deposited by feedlot cattle from across the central and western USA. Our secondary goal was to genotype isolates of C. parvum from feedlot cattle to help facilitate proper identification of mammalian sources of waterborne C. parvum. Based on 5274 fecal samples from 22 feedlots in seven states (California, Washington, Colorado, Oklahoma, Texas, Nebraska, and South Dakota), we estimated a point prevalence of C. parvum of 0.99 to 1.08% in fecal material from feedlot pens from a wide range of climates and a diverse range of feedlot management systems. On average, fresh fecal material from throughout feedlot systems (recent arrivals to nearing slaughter) contained about 1.3 to 3.6 oocysts/g feces, which roughly translates to about 2.8 x 10(4) to 1.4 x 10(5) oocysts/animal per day.

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“…[64] We assume that the biological decay rate of oocysts is 3.48 Â 10 À6 hr À1 [Robertson et al, 1992] regardless of whether microorganisms are attached to soil particles or not. This rate could be modified with further information about temperature and soil moisture content prior to storm events [Walker et al, 2001]. Hence k di , i = 1, .…”

Section: Parameter Estimation From Experimental Datamentioning

confidence: 99%

A combined microscopic and macroscopic approach to modeling the transport of pathogenic microorganisms from nonpoint sources of pollution

Yeghiazarian

Walker

Binning

et al. 2006

Water Resources Research

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[1] Recent outbreaks of cryptosporidiosis raise serious concerns about the effectiveness of watershed management in controlling the risk of contamination by pathogens. A modeling strategy that takes into account the inherent randomness of the occurrence and transport of pathogens in surface water is important for accurate risk assessment and prediction of water contamination events. This paper presents a stochastic Markov model of microorganism transport, with distinct states of microorganism behavior capturing the microbial partitioning between solid and aqueous phases in runoff and soil surface, including the partitioning among soil particles of various sizes. A connection between the soil sediment and microbial transport is established through the incorporation of an erosion model (WEPP) into the microorganism transport model. Probability distribution functions of microorganism occurrence in time and space are constructed, and their properties are analyzed. A deterministic mathematical model of coupled pathogen and sediment transport is developed in parallel to parameterize the Markov process. The numerical values for the Markov model parameters were derived from two sets of experimental data. Model results show that areas with clay soils are more likely than sandy soils to contribute to contamination events and that the most influential transport parameters are the saturated hydraulic conductivity, rainfall intensity, and topographic slope.

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Effects of Combined Water Potential and Temperature Stresses on Cryptosporidium parvum Oocysts

Cited by 9 publications

References 0 publications

Environmental inactivation of Cryptosporidium oocysts in catchment soils

Environmental inactivation of Cryptosporidium oocysts in catchment soils

Environmental Load ofCryptosporidium parvumOocysts from Cattle Manure in Feedlots from the Central and Western United States

A combined microscopic and macroscopic approach to modeling the transport of pathogenic microorganisms from nonpoint sources of pollution

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