Radiofrequency-Induced Thermal Inactivation of Toxoplasma gondii Oocysts in Water

Authors

  • K. E. Wainwright,

    1.  Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA
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  • M. Lagunas-Solar,

    1.  Chemistry and Agriculture Program, Crocker Nuclear Laboratory, University of California, Davis, CA, USA
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  • M. A. Miller,

    1.  Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA
    2.  Marine Wildlife Veterinary Care and Research Center, California Department of Fish and Game, Santa Cruz, CA, USA
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  • B. C. Barr,

    1.  Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA
    2.  California Animal Health and Food Safety Laboratory, University of California, Davis, CA, USA
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  • A. C. Melli,

    1.  Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA
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  • A. E. Packham,

    1.  Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA
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  • N. Zeng,

    1.  Chemistry and Agriculture Program, Crocker Nuclear Laboratory, University of California, Davis, CA, USA
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  • T. Truong,

    1.  Chemistry and Agriculture Program, Crocker Nuclear Laboratory, University of California, Davis, CA, USA
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  • P. A. Conrad

    1.  Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA
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Dr P. A. Conrad. Department of Pathology, Microbiology and Immunology, 1 Shields Avenue, School of Veterinary Medicine, University of California, Davis, CA, USA.
Tel.: (530) 752-7210; Fax: (530) 752-3349;
E-mail: paconrad@ucdavis.edu

Summary

Toxoplasma gondii, a ubiquitous parasitic protozoan, is emerging as an aquatic biological pollutant. Infections can result from drinking water contaminated with environmentally resistant oocysts. However, recommendations regarding water treatment for oocyst inactivation have not been established. In this study, the physical method of radiofrequency (RF) power was evaluated for its ability to inactivate T. gondii oocysts in water. Oocysts were exposed to various RF energy levels to induce 50, 55, 60, 70 and 80°C temperatures maintained for 1 min. Post-treatment oocyst viability was determined by mouse bioassay with serology, immunohistochemistry and in vitro parasite isolation to confirm T. gondii infections in mice. None of the mice inoculated with oocysts treated with RF-induced temperatures of ≥60°C in an initial experiment became infected; however, there was incomplete oocyst activation in subsequent experiments conducted under similar conditions. These results indicate that T. gondii oocysts may not always be inactivated when exposed to a minimum of 60°C for 1 min. The impact of factors such as water heating time, cooling time and the volume of water treated must be considered when evaluating the efficacy of RF power for oocyst inactivation.

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