If a cat stays indoors, they do not come in contact with any parasites.
Much better explained here by Cornell:
http://www.vet.cornell.edu/fhc/resources/brochure/toxo.html
"Toxoplasmosis in Cats
Toxoplasmosis, a disease of cats and other mammalian species, is caused by a parasitic protozoan, Toxoplasma gondii. Protozoa are single-celled organisms that are among the simplest creatures in the animal kingdom. Although infection with Toxoplasma is fairly common, actual disease caused by the parasite is relatively rare.
The Life Cycle of Toxoplasma
Cats, domestic and wild, are the definitive host (host in which the adult, or sexually mature stage, of the parasite is produced) and are the parasite's primary reservoir of infection. Domestic cats are important in transmission of Toxoplasma to other animals and human beings, which become involved only as intermediate hosts of the parasite. Consumption of raw meat tissues is another important means of transmission.
Cats acquire Toxoplasma infection by eating any of the three infective stages of the parasite: cyst, oocyst, or tachyzoite. Following ingestion of cysts in infected prey (rodents or birds), the intraintestinal infection cycle begins. This cycle occurs only in members of the cat family. The organisms multiply in the wall of the small intestine and produce oocysts, which are then excreted in great numbers in the feces for two to three weeks. Within five days the shed oocysts may sporulate, becoming infectious to other animals and to humans. Sporulated oocysts are highly resistant to environmental conditions and can survive in moist shaded soil or sand for many months.
During the intraintestinal infection cycle in the cat, some Toxoplasma organisms released from the ingested cysts penetrate more deeply into the wall of the intestine and multiply as tachyzoite forms. Very soon these forms spread out from the intestine to other body sites, starting the extraintestinal infection cycle. Eventually the cat's immune system restrains this stage of the organism, which then enters a dormant or "resting" stage by forming cysts in muscles and brain. Most cysts probably remain dormant for the life of the host. The extraintestinal infection cycle occurs not only in cats but also in the intermediate hosts (including humans).
Most healthy exposed cats shed oocysts during acute infection with Toxoplasma, but will not shed them after the acute infection. Even in those few cats that do re-excrete oocysts after another exposure to Toxoplasma, the number of oocysts shed is smaller and may even be insufficient to transmit the parasite effectively.
Ingestion of tissue cysts in infected prey or in other raw meat is probably the most common route by which cats are exposed to Toxoplasma. Congenital infection (transmission from mother to fetus) occurs in sheep, goats, and humans, but is much less common in cats."