A very nasty and 100% fatal disease. https://en.wikivet.net/Snake_Cryptosporidiosis
Disinfectants like chlorine bleach, F10, and chlorhexidine don't kill it. It can also lay dormant for months. Because the transmission is fecal-oral it's a big problem for people who keep their lizards in colonies, if they happen to introduce one that has the disease but isn't showing symptoms yet. Fecal exams often return false negative results.