The persistence of Toxoplasma gondii tissue cysts in organs
of cats (definitive host) and rodents (intermediate hosts) was
studied. Nine cats, 12 rats, and 12 mice were fed T. gondii
oocysts and their organs were digested in pepsin and then
bioassayed for bradyzoites in mice. Of 9 cats killed 37 or 51 days after
feeding 102 (2 cats), 103 (3 cats) or 104
(4 cats) oocysts
of the VEG strain, tissue cysts were found in each cat; in the tongue of
9, in the heart of 5, in the brain of 4, and in the
eyes of 1 cat. The dose had no effect on the distribution of tissue cysts
in cats. Twelve rats were each fed 105 oocysts of
the VEG strain of T. gondii and killed 21, 29, 64 or 237 days
later.
At each time-period, 11 tissues of 3 rats were pooled
and bioassayed in mice. Tissue cysts were found in the brain, skeletal
muscle, heart and kidneys of rats at each killing time;
in the lungs, intestines, and mesenteric lymph nodes in 3 of 4 instances;
in the tongue, liver, and eyes in 2 instances and
in the spleen in 1 instance. Also, using the same procedures and sampling
the same 11 tissues as used for rats, tissue cysts
were seen in all organs except in the tongue and liver of 3 mice killed
on day 82 after feeding the VEG strain. In 9 mice
(3 with each strain) fed oocysts of the ME-49, GT-1, or P89 T. gondii
strain and killed 62–130 days later, tissue cysts were
found consistently only in the brain. Thus, in rats and mice, most
tissue cysts were found in the brain and rarely in the
tongue. This was in marked contrast to the distribution of tissue cysts
in cats.
Toxoplasma gondii injected neurons localize to the cortex and striatum and have altered firing
