Comparative study of three different routes of experimental inoculation of the orf virus

Three different methods of inducing experimental infection of lambs with orf virus (ORFV), the cause of Contagious Ecthyma, were examined in nine animals; intradermal inoculation, subcutaneous injection and epithelial scarification. The objective was to identify the most appropriate experimental method to reproduce the disease with lesions of similar severity in all infected animals. Subcutaneous inoculation failed to reproduce orf lesions in two of the three infected animals, whereas both the groups that were inoculated by intradermal and scarification routes, respectively, displayed a significantly higher number of lesions at 12 dpi than the group inoculated subcutaneously. However, the lesions following scarification spread from the inoculation site with no ORFV-associated lesions found in other areas of the mucous membrane or skin. Finally, following intradermal inoculation, ORFV-associated lesions developed homogeneously in all infected animals, with lesions progressing from the point of inoculation in different areas of the skin of the lips, yet also spreading to the interior of the mouth, gums, palate and tongue, as occurs in natural infections. Thus, it was concluded that for studies investigating the efficacy of new approaches to treatment and vaccination for improved welfare of affected animals and control of ORFV transmission, the most appropriate route for experimental ORFV infection is intradermal inoculation.