Cryptosporidium

After drinking contaminated water, oocysts excyst in the intestine of various mammals, including humans. Sporozoites penetrate the intestinal epithelium, encysting just beneath the brush border. Each one undergoes schizogony to produce 8 merozoites. (The process is also called merogony.) The meront (or schizont) containing the merozoites ruptures and the merozoites infect new cells. This process of infection-schizogony-merogony continues for an indefinitie period of time. Some merozoites infect cells and develop into macro- and micro-gametocytes. Microgametes fertilize macrogametes and produce a zygote. A cyst forms around the zygote. This oocyst ruptures free and passes down the intestinal tract. Sporulation is rapid, and is completed before the feces are passed. Each oocyst contains 4 sporozoites. Most oocysts have a thick wall that is resistant to environemental conditions and permits transmission between hosts. A small proportion of oocysts have thin walls and excyst while still in the host, leading to autoinfection.