Coccidia is a one-celled microscopic organism that can wreak havoc with your little pup's intestinal track. Fortunately, coccidia is fairly rare in dogs, but it is a risk especially if your dog is living closely with other animals. If your dog is infected with coccidia eggs, he'll likely have the following symptoms: diarrhea, lack of appetite, general weakness, anemia and dehydration. Your dog might not show all these symptoms, but if you see a number of them, take your dog to the vet to see what's going on.
Coccidia can get into your dog through a contaminated environment, which is why these organisms are mostly found in puppies living in crowded conditions. Once one dog has it, the coccidia organisms get passed through his stool, which can then infect the environment, and the water and food of the other dogs if not properly cleaned up immediately. As the other dogs ingest the coccidia organisms, the eggs will now implant in the other dogs' intestinal tracts. However, you should know that a dog with coccidia might not show any symptoms immediately; the little eggs might just be growing inside of him. Usually some sort of stressor will cause the coccidia to become active, at which point your dog will probably start to display any of the symptoms listed above.
If your dog is suffering from coccidia, you'll have to take him to the vet and he will probably prescribe sulfa drugs and antibiotics to kill the organisms. You'll also have to clean your dog's living area thoroughly. Use strong (but doggy-friendly) disinfectants or boiling water to clean surfaces. You'll probably want to wash (or throw out, if necessary) any bedding your dog uses. The best way to prevent coccidia is to make sure your dog's living area is kept clean and to pick up any stool as soon as it appears.