Final answer:
The watery diarrhea caused by rotavirus is due to an increase in osmotic pressure in the lumen of the intestine.
Step-by-step explanation:
The watery diarrhea caused by rotavirus is due to increase in osmotic pressure in the lumen of the intestine. Rotaviruses are double-stranded RNA viruses that primarily spread through the fecal-oral route. Once inside the intestines, the virus attaches to epithelial cells and releases a toxin that increases cyclic AMP levels, activating a chloride channel. This results in the release of ions into the intestinal lumen, causing an osmotic pressure increase and water entering the lumen, leading to watery diarrhea.