Rotavirus: A virus that is a leading cause of severe diarrhea and dehydration in young children. Abbreviated RV. Almost everyone catches RV before entering school, but, with rehydration and good nutrition, nearly all recover fully. Aside from causing acute infantile gastroenteritis and diarrhea in young children, RV is typically accompanied by low-grade fever. Immunization of infants with a vaccine against RV was halted in 1999 because of reports of deaths due to bowel obstruction (from intussusception of the bowel) following vaccination, but a newer vaccine was made available in 2006.