Primary infection can also occur in the bones and lungs. Dogs with the gastrointestinal form of pythiosis have severe thickening of one or more portions of the gastrointestinal tract that may include the stomach, small intestine, colon, rectum, or in rare cases, even the esophagus. The resulting pathology results in anorexia, vomiting, diarrhea (sometimes bloody), and abdominal straining.