Intestinal Parasite Problems ---------------------------- Intestinal parasites are usually not a significant problem in pet guinea pigs. A protozoan (one-celled organism) parasite may cause coccidiosis in guinea pigs. Signs of this disease include weakness, diarrhea and severe weight loss. Pinworm infections of guinea pigs usually go unnoticed. Both of these parasitisms can be diagnosed by a veterinarian by stool examinations. Both are treatable using specific drugs prescribed by the veterinarian. Neither parasite problem is transmissible to people.