Effect of gamma irradiation on unsporulated and sporulated Toxoplasma gondii oocysts

The effect of Cs-137 irradiation on unsporulated and sporulated Toxoplasma gondii oocysts was investigated as a model system for sterilisation of fruit contaminated with other coccidia such as Cyclospora or Cryptosporidium. Unsporulated oocysts irradiated at greater than or equal to 0.4 to 0.8kGy sporulated but were not infective to mice. Sporulated oocysts irradiated at greater than or equal to 0.4kGy were able to excyst, and sporozoites were infective but not capable of inducing a viable infection in mice. Toxoplasma gondii was detected in histologic sections of mice up to 5 days but not at 7 days after feeding oocysts irradiated at 0.5kGy. Transmission electron microscopy revealed that sporozoites from irradiated oocysts penetrated enterocytes and all cells in the lamina propria except for red blood cells. Sporozoites appeared normal ultrastructurally and formed a typical parasitophorous vacuole containing a well-developed tubulovesicular membrane network. Raspberries inoculated with sporulated T. gondii oocysts were rendered innocuous after irradiation at 0.4kGy. Results indicate that irradiation at 0.5kGy is effective in "killing" coccidian oocysts on fruits and vegetables. (C) 1998 Australian Society for Parasitology. Published by Elsevier Science Ltd.