The protozoan parasite Toxoplasma gondii is increasingly recognized as a waterborne pathogen. Infection can be acquired by drinking contaminated water and conventional water treatments may not effectively inactivate tough, environmentally resistant oocysts. The present study was performed to assess the efficacy of 2 commonly used chemicals, sodium hypochlorite and ozone, to inactivate T. gondii oocysts in water. Oocysts were exposed to 100 mg/L of chlorine for 30 min, or for 2, 4, 8, 16, and 24 hr, or to 6 mg/L of ozone for 1, 2, 4, 8, or 12 min. Oocyst viability was determined by mouse bioassay. Serology, immunohistochemistry, and in vitro parasite isolation were used to evaluate mice for infection. Initially, mouse bioassay experiments were conducted to compare the analytical sensitivity of these 3 detection methods prior to completing the chemical inactivation experiments. Toxoplasma gondii infection was confirmed by at least 1 of the 3 detection methods in mice inoculated with all doses (10(5)-10(0)) of oocysts. Results of the chemical exposure experiments indicate that neither sodium hypochlorite nor ozone effectively inactivate T. gondii oocysts, even when used at high concentrations.

Pulsed UV (PUV) power techniques were studied as a nonthermal, residue-free alternative to contact pesticides and to evaluate the surface disinfection of fresh fruits using this type of extremely rapid, high-peak power UV beams. Coherent 248-nm beams from excimer lasers were used to simulate a variety of pulsed light sources now commercially available. Surface disinfection on a series of fresh fruits (i.e., apples, kiwi, lemon, nectarines, oranges, peaches, pears, raspberries, and grapes), representing economically important commodities, were studied and evaluated. Plant (fungal) pathogens were rapidly (<10 s), efficiently (>5 log), and reproducibly killed on fruit surfaces. However, in naturally infected or inoculated (sprayed) fruits, a fraction of the inoculum may penetrate into the epidermis or locate in injured tissue in crevices or in surface irregularities. Under these conditions, only partial disinfection was obtained due to UV shielding (shadowing) effects, which prevent the highly directional, coherent PUV beam from reaching its target. For maximum disinfection efficiency, coherent PUV sources must be combined with dispersing reflectors, and fruits must be handled to ensure uniform exposure to multidirectional incident beams. New, existing, noncoherent, broadband, pulsed light beams (high in UV emission) from arc lamps appear to provide adequate PUV light sources capable of meeting the conditions for commercial applications in slight-modified conveyorized operations. Therefore, PUV techniques may provide effective, commercial-scale, reliable, and viable residue-free alternatives to chemical (contact) pesticides.

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Inactivation of Toxoplasma gondii oocysts occurred with exposure to pulsed and continuous UV radiation, as evidenced by mouse bioassay. Even at doses of ≥500 mJ/cm2, some oocysts retained their viability.