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Published on: April 29, 2020
Determining UV inactivation of Toxoplasma gondii oocysts by using cell culture and a mouse bioassay
Michael W Ware1, Swinburne A J Augustine, David O Erisman
1National Exposure Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268, USA.
Abstract:
The effect of UV exposure on Toxoplasma gondii oocysts has not been completely defined for use in water disinfection. This study evaluated UV-irradiated oocysts by three assays: a SCID mouse bioassay, an in vitro T. gondii oocyst plaque (TOP) assay, and a quantitative reverse transcriptase real-time PCR (RT-qPCR) assay. The results from the animal bioassay show that 1- and 3-log(10) inactivation is achieved with 4 mJ/cm(2) UV and 10 mJ/cm(2) low-pressure UV, respectively. TOP assay results, but not RT-qPCR results, correlate well with bioassay results. In conclusion, a 3-log(10) inactivation of T. gondii oocysts is achieved by 10-mJ/cm(2) low-pressure UV, and the in vitro TOP assay is a promising alternative to the mouse bioassay.
Insights
UV disinfection effectively inactivates Toxoplasma gondii oocysts in water. The in vitro T. gondii oocyst plaque (TOP) assay reliably predicts inactivation, offering a viable alternative to animal bioassays for water treatment validation.
Area of Science:
- Environmental microbiology
- Water disinfection technologies
- Parasitology
Background:
- Toxoplasma gondii oocysts pose a risk in water supplies.
- UV disinfection is a potential water treatment method.
- The efficacy of UV on T. gondii oocysts requires precise definition.
Purpose of the Study:
- To determine the effectiveness of UV irradiation for inactivating T. gondii oocysts.
- To compare the reliability of different assays for assessing UV inactivation.
- To establish optimal UV doses for water disinfection.
Main Methods:
- Evaluation of UV-irradiated T. gondii oocysts using SCID mouse bioassay.
- Assessment via in vitro T. gondii oocyst plaque (TOP) assay.
- Quantification using quantitative reverse transcriptase real-time PCR (RT-qPCR) assay.
Main Results:
- 1- and 3-log(10) inactivation achieved with 4 mJ/cm(2) and 10 mJ/cm(2) UV, respectively.
- TOP assay results correlated well with animal bioassay outcomes.
- RT-qPCR assay results did not correlate with bioassay findings.
Conclusions:
- 10 mJ/cm(2) low-pressure UV achieves a 3-log(10) inactivation of T. gondii oocysts.
- The in vitro TOP assay is a promising and reliable alternative to the mouse bioassay.
- UV disinfection, validated by the TOP assay, is effective for T. gondii control in water.
