A protozoan parasite known as Cryptosporidium parvum (C. parvum), one of the most common waterborne pathogens in the world, is the cause of a horrible gut infection called cryptosporidiosis. One of the things that makes this parasite so insidious is that it is one of the few that can be passed to animals from humans and vice versa. The parasite is present in nearly 90% of all untreated water, and can be easily reintroduced to treated water through environmental contamination.
The virus is excreted through the bowels and is most commonly contracted through inadvertent oral-fecal contact. C. parvum acts by forming oocysts, which are hardy structures made up of a wall of immature forms of the parasite. These are excreted in high numbers through the feces, and may continue to be excreted for up to 2 months after an infection. Up to 1 million oocysts may be present in just one stool. However, a mere 1 to10 oocysts are all that is needed to cause illness in a healthy human or pet. Once infected, it can take up to 30 days to exhibit symptoms, providing further opportunities for the oocysts to spread.
Unfortunately, there is no treatment for cryptosporidiosis beyond letting it run its course and mitigating the resulting nausea, vomiting, and dehydration. Therefore, this parasite is dangerous for those very young, very old, or immunocompromised. The best way to avoid C. parvum is to maintain good hygiene. This includes washing your hands after going to the bathroom or coming into contact with human or animal stool, as well as before eating. If you are diagnosed with cryptosporidiosis, you can prevent spreading it to others by avoiding any type of communal bathing areas where the parasites could be washed off your body and onto others. Finally, the Center for Disease Control notes that soaking a contaminated surface for 20 minutes in a solution of 3% hydrogen peroxide, then rinsing it thoroughly, will kill 99% of the C. parvum on that surface.