Submitted to: American Society of Parasitologists
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2000
Publication Date: N/A
Technical Abstract: Cats are important in the epidemiology of Toxoplasma gondii because they can excrete millions of environmentally resistant oocysts. Oocyst shedding by cats is more efficient after ingesting tissue cysts than after ingesting tachyzoites or oocysts of T. gondii. In the present study, the number of oocysts shed by cats fed free bradyzoites was determined. Tissue cysts of the VEG strain of T. gondii were separated from the brains of chronically infected mice by Percoll gradient. Bradyzoites were liberated from tissue cysts by treatment with pepsin. Free bradyzoites were filtered through a 3 um filter to remove larger particles. Bradyzoites were counted in a hemocytometer. Starting with an initial count of 1 million bradyzoites per ml seven (10-1 to 10-7) 10-fold dilutions were made in RPMI tissue culture medium. The viability of bradyzoites was verified by bioassay in mice. Dilutions calculated to have 1, 10, 100, and 1,000 bradyzoites were fed to 4, 4, 2, and 2 cats, respectively; the inoculum (1ml/cat) was poure in the mouth of the cat. The total number of oocysts shed by each cat was determined. Three of 12 cats fed bradyzoites shed oocysts with prepatent periods of 6 or 7 days. The total number of oocysts shed were 238 million, 52 million, and 210 million after feeding 1, 10, and 1,000 bradyzoites, respectively. Results indicate the enormous reproductive potential of T. gondii oocyst shedding by cats and that the number of oocysts shed is not always proportional to the dose of bradyzoites ingested.