Oocysts

Oocysts are the resistant, thick-walled stages formed when two gametes fuse in the life cycles of certain sporozoan parasites, including Cryptosporidium, Toxoplasma, and Cyclospora. They are extremely tough, surviving chlorination and temperature extremes far better than the vegetative forms, though the degree of resistance varies among species and conditions. In food and water safety they are significant because oocysts shed in animal or human faeces can contaminate produce, water, and ready-to-eat foods, causing outbreaks of cryptosporidiosis and toxoplasmosis. Control depends on filtration of water supplies, thorough washing of produce, adequate cooking, and good agricultural practices that keep faecal contamination away from crops.