Parasitic infections can cause various symptoms in adults, including abdominal pain, bloating, diarrhea, constipation, and fatigue. Some people may also experience nausea, vomiting, weight loss, and Anemia. Itching around the anus, especially at night, can be a sign of pinworms. If you experience any of these symptoms, it is important to see a professional Healthcare practitioner or your GP for an accurate diagnosis.