Persistence of encysted Toxoplasma gondii in tissues of pigs fed oocysts.

Ten pigs were fed 100 to 10,000 Toxoplasma gondii oocysts. Two pigs died 7 and 11 days later, and 8 pigs were euthanatized at days 38, 38, 91, 126, 168, 169, 170, and 171. From the euthanatized pigs, portions of 15 organs digested in pepsin-HCl solution were inoculated into mice, as a bioassay for viable T gondii. Such organisms were isolated from the brain and heart of these 8 pigs, from the tongue of 7, from thigh muscles of 5, from the diaphragm of 4, from kidneys, liver, and small intestines of 2, and from salivary glands and eyes of 1 pig; but not from lungs, spleen, spinal cord, mesenteric and prescapular lymph nodes of any pig. Results indicate that T gondii can persist in edible tissues of living pigs for at least 171 days and that heart and brain may be the most suitable porcine tissues for epizootiologic surveys.