Final answer:
Oocysts of Cystoisospora spp. become infective within 1-5 days after being shed into the environment, similar to the oocysts of T. gondii. Sporulation occurs in the environment transforming the oocysts into an infective form which can then be ingested by intermediate hosts.
Step-by-step explanation:
The oocysts of Cystoisospora spp., which are similar to those of Toxoplasma gondii, become infective when they undergo sporulation in the environment. This process transforms unsporulated oocysts into their infectious form and for T. gondii, it specifically takes 1-5 days after being shed in a cat's feces to become infective. Once animals or humans ingest these sporulated oocysts, they can develop an infection. With that in mind, it is important to note that indirect context of related organisms suggests that Cystoisospora spp. oocysts would follow a similar timeline to become infective. The oocysts are ingested by intermediate hosts, like birds and rodents, from contaminated soil, water, or plant material. Subsequently, the oocysts transform into tachyzoites, which then localize in neural and muscle tissues, leading to the development of tissue cysts. Partners in this life cycle, such as humans, may become infected by eating undercooked meat from infected animals that contain tissue cysts, exposing them to the risk of parasitic infection.