In experiments, animals can be infected by intranasal, scarification, subcutaneous, or intravenous inoculation.
Flies feeding on lesions are potential mechanical vectors.
In areas where SP and GP are endemic, about half of newborn lambs and kids are susceptible to them. The long survival of the viruses in scabs and the continual presence of susceptible animals ensures persistence of the diseases. Herding systems and gathering animals at wells, markets, etc., provide ideal conditions for spread.