Strategies to reduce transmission of Toxoplasma gondii to animals and humans.

Toxoplasma gondii is found in the tissues of food animals and is an important cause of abortion and mortality in sheep and goats throughout the world. It causes mental retardation and loss of vision in congenitally infected children and death in immunosuppressed patients. A live vaccine, using a nonpersistent strain of T. gondii, is available in New Zealand, the UK and Europe which prevents T. gondii abortion in sheep. A live vaccine using a mutant strain of T. gondii (T-263) is being developed in the USA to reduce oocyst shedding by cats. As yet, there are no drugs to kill T. gondii tissue cysts in human or animal tissues. Freezing to -12 degrees C, cooking to an internal temperature of 67 degrees C, or gamma irradiation (0.5 kGy) can kill tissue cysts in meat.