Civil & Environmental Engineering
Retention and Release of Cryptosporidium parvum Oocysts by Experimental Biofilms Composed of Natural Stream Microbial Communities
Cryptosporidium is a group of waterborne protozoan parasites that cause significant gastrointestinal disease in humans. The potential exists for these parasites to accumulate in stream or pipe surface biofilms and to be subsequently released to contaminate the water supply. Natural microbial assemblages were collected from three streams for three seasons (fall, winter, and spring) and used to grow biofilms in laboratory microcosms. These biofilms were then exposed to Cryptosporidium parvum oocysts via continuous inflow to determine daily influx, efflux, and biofilm retention and sloughing. Daily oocyst counts showed that oocysts attached to the biofilm quickly (within hours) and released slowly (within days). In these experiments, at least 40% of the oocysts added to the system attached to the biofilm in the first 72 hours, and at least 20% of the oocysts remained attached to the biofilm beyond 72 hours after the oocyst supply was removed. Although variation across site and season exists, likely as a result of variable microbial communities, all biofilms captured at least 40% of the oocysts and retained some of those oocysts for at least five days. The biofilm attachment and detachment dynamics of C. parvum oocysts have important implications for public health and suggest that biofilm monitoring should be included in routine water supply monitoring.
Influence of Dissolved Organic Carbon on the Viability and Infectivity of Cryptosporidium
Cryptosporidium is a group of waterborne protozoan parasites that cause significant gastrointestinal infection in humans. The challenges associated with pathogen removal from water supplies, combined with the lack of medical cure for this infection, makes environmental controls important to investigate. The infectivity of Cryptosporidium oocysts under different environmental conditions must be examined to determine the risk of human exposure and infection. The research goal is to understand the direct effect of dissolved organic carbon (DOC) on the viability and infectivity of Cryptosporidium, as well as its indirect effects through other related environmental factors, including pH and UV radiation (UVR). This project examines direct and indirect effects of DOC on the viability and infectivity of Cryptosporidium using DAPI/PI staining, an excystation assay, and an in-vitro cell culture infectivity assay. The results show that both pH and DOC have significant impacts on Cryptosporidium viability and infectivity. This negative effect of DOC appears to be greater than the protective effect DOC has on oocysts by blocking damaging UVR. By identifying the influence of DOC and its interactions with other ecological factors on Cryptosporidium, watersheds at risk for supporting infectious oocysts can be identified and targeted for enhanced protection and/or water treatment.