​Dermal Response to Experimental Orfvirus (ORFV) Infection in Goats, Mice and Rabbit

Abstract

Background: During a study on the outbreak of orf in goats, it was intended to study the disease transmissibility in different hosts from field samples and ascertain the infective potential of the agent in laboratory animals compared to goats. Methods: Cutaneous clinical materials from orf virus (ORFV) infected goats was used to experimentally infect naive goats, rabbits and mice and ascertain its infective potential and transmissibility in different hosts. The processed inoculum was applied topically to mimic a natural transmission through injured skin. Regular skin biopsies were taken that revealed characteristic macroscopic and microscopic lesions typical of orf. Result: Virus inoculum applied on abraded skin in goats successfully established the lesions of orf. A parallel inoculation in rabbit and mice could not successfully reproduce the disease in these unnatural hosts beyond a subtle vesicular stage on 3 dpi with subsequent healing by 7 dpi. The lesions in goats regressed spontaneously by 28 days post-infection (dpi). Intracytoplasmic inclusions were associated only in the vesicular stage. Immunopathological progression was observed by immunoperoxidase staining of CD4+ and CD8+ T-cells which were found to appear by day 5 in the dermis and became more abundant and distributed by day 8, but subsequently reduced in number by 15 dpi. CD4+ cells were found to be more numerous and widespread. Viral antigen in tissues could be demonstrated by 4 dpi by immunohistological methods that increased in signal intensity progressively and disappear by 28 dpi. Similarly, viral nucleic acid in the skin could be detected on day 8 dpi but not on 28 dpi by PCR. The present experiment depicts the ease of disease transmissibility through traumatized skin in the primary hosts, but establishment in unnatural hosts may not be readily achieved. The infection was self-limiting with possibly no virus latency as indicated by immunofluorescence and PCR studies.