Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2002
Publication Date: March 22, 2002
Citation: Dubey, J.P. 2002. Tachyzoite-induced life cycle of toxoplasma gondii in cats. Journal of Parasitology 88:713-717.
Interpretive Summary: Toxoplasma gondii is a single-celled parasite of livestock and humans. It causes mental retardation in congenitally infected children and abortion in livestock. There are 3 infectious stages of this parasite: tachyzoites, bradyzoites and oocysts. Cats are the reservoir hosts of T. gondii because they are the only hosts that can excrete in their feces enviromentally- resistant stage called oocysts. Humans become infected by any of these 3 stages from oocysts. The lifecycle of Toxoplasma in the cat is known after ingesting bradyzoites and oocysts but not after ingesting tachyzoites. A scientist at the Beltsville Agricultural Research Center has studied the lifecycle of Toxoplasma in cats after feeding tachyzoites. The results will be of interest to veterinarians, parasitologists, and public health workers.
Tachyzoite-induced cycle of Toxoplasma gondii was studied in 46 cats. Tachyzoites of the M-7741 or Me-49 strains of T. gondii were administered orally to cats by pouring in the mouth or by stomach tube, or by intra- intestinal inoculation. Ten weaned cats that had been inoculated with tachyzoites directly in intestine were killed 1, 3, 6, 9, 12, 15, 18, or 25 5days later and their tissues were studied histologically and bioassayed in mice. Toxoplasma gondii was demonstrable in blood of 8 and in other tissues of all of these 10 cats. Four of 5, 1-to-8-day-old cats fed tachyzoites by stomach tube became infected with T. gondii and 1 became ill due to toxoplasmosis. All 19 weaned cats fed tachyzoites (poured in the mouth) became infected and 6 died of acute toxoplasmosis 9-15 days after feeding T. gondii. Six of 12 weaned cats fed tachyzoites by a stomach tube became infected but were asymptomatic. Overall, 12 of 26 cats observed for r19 days or more shed oocysts with prepatent periods of 19 days or more wit the sole exception of 1 cat that shed oocyst with a prepatent period of 5 days. Entero-epithelial stages of T. gondii were not found in any cat before oocysts were shed. Cats shed up to 360 million oocysts in a day and oocysts were shed for 4 to 6 days.