**3. Human gut and viral infection**

For decades human gut-associated pathogenic viruses are known for many gastrointestinal diseases as gastroenteritis. Following are the main group of viruses has been identified. Rotavirus, adenovirus (serotype 40 and 41), astrovirus, calicivirus, norovirus, torovirus, herpesviruses, coxsackieviruses, human papillomaviruses [3], Norwalk-like viruses, coronaviruses, picornaviruses, Sapporo-like viruses [4, 5]. They infect epithelial cell linings, mucosal linings of the stomach and small intestine, a specific portion of epithelium in the intestine. Depending upon the infection type observed, different samples are used for detection of the infectious agent. In general, feces sample used for general microbiological examination during gut-associated infection [6, 7]. Apart from feces, gastric biopsy, gastric juice, saliva [8, 9] duodenal fluid, cotton swabs [5] are collected. These samples are very essential for diagnosis as they directly contain the pathogen.
