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Persistence of Cryptosporidium parvum in bovine feces during summer and winter exposure Story, Keith Trizin


Grazing cattle on forested crown lands can be beneficial to the local economy but may also pose a risk to the drinking water extracted from the watershed. A major disturbance that the cattle present to watersheds is the deposition of protozoan pathogens such as Cryptosporidium parvum in their manure. Fecal pathogens deposited near riparian zones can be transmitted into water systems when disturbed by elevated river flow. Although cattle are out of pasture during spring freshet when water flow is high, their feces remain near rivers and streams. If C. parvum persists in feces beyond grazing season and into spring freshet, it may serve as a point source for disease. Nested PCR targeting the Cryptosporidium 18S rRNA gene was used to assess the persistence time of C. parvum oocysts in bovine feces during both the winter and summer seasons in the Okanagan valley, British Columbia. Nested PCR was found to have a limit of detection less than one oocyst per reaction and was of comparable sensitivity to quantitative real-time PCR (3.2 oocyst LOD). Ruptured oocysts were not detectable by nested PCR, Shading, precipitation, freezing/thawing events, temperature, and ultraviolent light were evaluated as factors associated with persistence time. In winter, heavily and moderately forested sites contained detectable C. parvum for less than 67 days, whereas lightly shaded sites showed persistence up to 106 days. Fecal pats were subjected to simulated river flow after winter exposure and no samples leached C. parvum. In summer experiments, feces in lightly forested plots contained no oocysts by 71 days of exposure, whereas heavily and moderately forested plots showed persistence up to 261 and 227 days, respectively. Freeze-thaw events as well as direct ultraviolet light exposure are supported as predominant factors against C. parvum persistence in winter and summer exposures. After three freeze-thaws, 59% of the oocyst population was lost and only 19.3% of the remaining oocysts contained intact cell walls. This research has application in grazing operations as it is provides unprecedentedly low detection limits for monitoring seasonal C. parvum persistence in different shading conditions.

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