Faecal-oral transmission. Highly infectious; spreads rapidly.
Group A RV: enzootic in domestic animals throughout the world. All animals become infected sooner or later & all have antibody. The young excrete RV in faeces, clinically or sub-clinically, as passive maternal antibody wanes in the gut (commonly in the second week of life in calves; before or after weaning in piglets). Adult cows and sows can act as reservoirs: excrete virus in faeces at parturition and a source of RV for the young.
Other groups: Less known but common in their respective species