"The organism is spread in the stool, so keeping non-infected pets away from the stool of infected pets is helpful but if they share a common environment it is highly likely that infection will occur. The infection may or may not cause clinical disease and treatment is generally considered to be necessary only for pets showing clinical signs. General cleanliness does not ensure that infections will not occur, but removal of contaminated stool reduces the potential for infection. The oocysts are supposed to be pretty resistant to most disinfectants and things like steam cleaning or flame guns may be necessary to actually kill the oocysts, which is impractical for most situations. Keeping access to mice down (especially for cats) is also a good idea.
Coccidia are easy to find using standard fecal floatation methods for fecal exams and are often present in sufficient numbers to show up if a small amount of stool is smeared on a glass slide, mixed with a small amount of saline and examined.
When Isospora species cause disease the most common form is watery diarrhea that is very profuse. Many kittens and puppies seem to just leak watery stools as if they have no control at all over their bowel movements, while others have a more "normal" diarrhea. Without treatment, the diarrhea might last for several weeks. With treatment the diarrhea might last several weeks, too --- but it does seem to cut down some on the duration of the diarrhea to treat affected puppies and kittens. The most commonly used medications are sulfonamide antiseptics, such as sulfadimethoxine (Albon Rx, Bactrovet Rx) given at 55mg/kg of body weight initially and then 27.5mg/kg per day for 4 to 7 days. The medication should be given until two days after symptoms of illness have disappeared. Lots of vets substitute trimethoprim/sulfa combination medications (Ditrim Rx, Tribrissen Rx, Bactrim RX) for this sulfadimethoxine, using a dosage of 15mg/lb of the combined product and this seems to work, too. While it is probably impossible to kill all the coccidia in a puppy with clinical disease using medications, it may help reduce the numbers of organisms that littermates and housemates are subjected to and to shorten the duration of clinical signs."
