This life cycle can take many routes, and many details were worked out only recently. Consequently, many of the stages are given names that are peculiar to this genus, even though they have parallels with typical coccidian life cycles. There are hundreds of suitable mammalian hosts and dozens of bird hosts, but the cat is the only host in which te sexual pahses of the life cycle can occur. Oocysts are ingested and excyst in the intestine. Sporozoites enter intestinal epithelial cells and multiply by a budding process. The trophozoites that are produced either continue with several rounds of asexual multiplication, or form gametes, as in other coccidians. Some may also enter the tissues of the host and become intracellular parasites in a variety of nucleated cells. Cysts may form is areas such as the brain. In non-cat hosts, after ingestion the oocyst ruptures and the sporozoites immediately penetrate the gut and are distributed throughout the body. Within nucleated cells they divide and form pseudocysts (bounded only by the cell membrane of the host cell) containing hundreds of tachyzoites. These burst and the tachyzoites infect other cells. As the immune response of the host develops, true cysts are eventually formed, containing large numbers of bradyzoites, and capable of persisting for many years. Cats can become infected by ingesting oocysts, tachyzoites, or bradyzoites. In various hosts including humans, an infection acquired by a non-immune host can transmit transplacentally to a fetus.