Applications of in-vitro cell culture for measuring infectivity and inactivation of Cryptosporidium parvum

Cryptosporidium parvum presents a significant problem for the water industry and public health officials because of its prevalence in sources of drinking water and its resistance to chlorine-based disinfectants; there is an urgent need for alternative, more effective disinfection strategies. Therefore, developing and evaluating methods for assessing the infectivity and inactivation of C. parvum oocysts are of paramount importance. Infectivity assays based on in-vitro cell culture have been developed as alternatives to human and animal-based assays to overcome ethical, cost, and practicality issues. Data obtained over a two-year period with an HCT-8 cell culture/RT-PCR infectivity assay generated an ID₅₀ of 99 oocysts (95% CI: 84-117) and demonstrated that the cell culture assay was equivalent to the standard CD-1 mouse model for measuring infectivity of C. parvum oocysts. Aggregate data generated over two years using the HCT-8 cell culture/RT-PCR assay to measure UV disinfection of C. parvum demonstrated that 2.4 mJ/cm² and 4.9 mJ/cm² were necessary to achieve 1-log₁₀ and 2-log₁₀ inactivation, respectively. This work demonstrated that an HCT-8 cell culture-based infectivity coupled with RT-PCR for detecting C. parvum infections is a practical tool that can provide valuable information about the efficacy of disinfectants and the infectivity of oocysts in environmental waters.