gastroenteritis stomach flu

gastroenteritis gastro colorectal villi intestine lining pathology mucosa gastrointestinal intestinal crypts epithelial cells colon small anatomical villus large bowel microvilli viral infection foodborne illness contaminated water cramping cramps probiotics contagious stomach pain diarrhoea clostridium difficile dehydration intestines nausea parasites visuses food poisoning gut symptoms diagnosis tummy