Final answer:
Most diarrheal diseases are of viral origin, particularly caused by viruses like norovirus and rotavirus, which are highly prevalent in the developing world and a leading cause of death in children.
Step-by-step explanation:
Most diarrheal diseases are of viral origin, such as those caused by norovirus and rotavirus. Viral pathogens are a major contributor to gastrointestinal illnesses, particularly in the developing world where acute viral gastroenteritis is a leading cause of death among children. Bacteria, like Vibrio cholerae and enteropathogenic Escherichia coli (EPEC), also play a significant role in diarrheal diseases. However, studies indicate that approximately 70% of childhood gastroenteritis cases are due to viral infections, with rotavirus being one of the most common causative agents.