Abstract
A comparative study on the clinico-pathological response of camels and sheep to cross-experimental infection with two virulent field orf viruses, originating from camels and sheep, was made. Sheep were completely refractory to infection with the camel orf virus. Equally the camels were resistant to infection with the orf virus originating from sheep. The sheep developed classical clinico-pathological lesions against the orf virus of sheep origin and gave a low level of seroconversion. The camels, which were inoculated with the camel orf virus, also showed classical clinico-pathological signs but no seroconversion was detected. The results were discussed in relation to the epidemiology of the disease in Saudi Arabia.