A lot of bunnies that are out on the street for a while develop coccidia. There are many different coccidia parasites, and most of them infect a particular species. Humans cannot contract rabbit coccidia, but they can transfer it from one bunny to another. Many adult bunnies have the parasite, but do not manifest any symptoms. In babies it is very dangerous. The parasite can cause terrible loose stools and cramping. Babies can die from the dehydration.
The test involves taking a fecal sample and floating it in a solution that drives out the parasite. Then, the parasite can be seen under a microscope. The treatment is a course of Albon that kills the parasite. The disease is highly contagious, so once a bunny has it they can infect anybun they live with, and can even reinfect themselves. The parasite travels from one bunny to another through the fecal pellets. I think bleach is effective at killing it on surfaces.
Some shelters routinely test and treat for coccidia, some do not. A particularly virulent strain was present in some of the bunnies that came from the great Reno bunny rescue, and these rabbits infected and killed other bunnies in the families that adopted them.