Historically, the disease has occurred in about ten year cycles and the spread of VS epidemics in the US follow a south to north geographical route. It tends to follow river valleys and the Rocky Mountains. Spread is also associated with pastures, humid conditions and wind currents. Geographically, the disease is limited to the western hemisphere and occurs as both endemics and epidemics. In these regions cases of VS are generally mild and occur in small numbers every 1-2 years.
Outbreaks tend to be seasonal and reach a peak in the late summer and early autumn.
Kentucky, Tennessee, North Carolina, Virginia and West Virginia. Disease spread through herds is most likely due to contact between animals and mechanically by insects and on fomites. Contact spread is probably by droplets. Over long distances VS spread may be due to the movement of infected animals and possibly by biting flies. Indirect losses from calf mortality and quarantine In beef production the greatest impact appears to be on calves with low market weights because they were weaned early from cows with painful teat lesions.