Impact of biofilm and other environmental factors on the fate and transport of Cryptosporidium oocysts.

摘要

Cryptosporidium (waterborne protozoan parasites) causes human gastrointestinal disease. With no cure for this infection, pathogen control is important to protect public health. Understanding the interactive effect of environmental factors, specifically dissolved organic carbon (DOC) and biofilms, on oocyst fate and transport will aid in understanding Cryptosporidium ecology and conditions for infectious oocysts.;DOC had variable impacts on Cryptosporidium infectivity through direct interaction and indirectly through reduced pH. During solar exposure, DOC did not shade oocysts from damaging wavelengths. The results were variable and cannot be broadly applied to control Cryptosporidium as DOC varies across landscapes.;In contrast to DOC, biofilms are ubiquitous and function similarly across sites. Oocysts quickly attached to biofilm surfaces during oocyst dosing. Following oocyst dosing, the oocysts retained by the biofilm decreased to a steady state within five days and remained for 25 days. Oocyst retention varied with each collection season, but was consistent across sites. Oocyst retention was not correlated with water quality; however, it was correlated with biofilm surface roughness. The biofilm had a limit to the number of oocysts attached as a result of biofilm roughness. Biofilms are often overlooked, but prove to be an important component in oocyst transport.;Biofilm's ability to protect oocysts from solar radiation was tested. Oocyst infectivity was reduced following solar exposure, but oocysts attached at the biofilm base received some protection, as the biofilm absorbed UV wavelengths. Sloughed oocysts were less permeable and more infectious than oocysts not associated with a biofilm, suggesting oocysts maintained association with biofilm material after sloughing.;Low oocyst concentrations are found in surface waters and difficult to detect by water sampling. Slides were used to monitor for Cryptosporidium in biofilms and compared to water samples. Oocysts were consistently detected in biofilm samples, but sporadically in water samples. Results support biofilm monitoring as a method to identify Cryptosporidium presence in a watershed and contamination hotspots.;Interactions between biofilms and Cryptosporidium oocysts have not been studied extensively, but are an important component of environmental oocyst fate and transport. Understanding these interactions may lead to more effective monitoring strategies and oocyst removal from water supplies.