Transplacental (vertical) transmission of Orf virus in mice (Mus musculus)

Contagious ecthyma, caused by Orf virus (Parapoxvirus), is enzootic in sheep and goats across Asia, Africa, and other regions of the world. Due to the self-limiting nature of the disease, it has been neglected for decades, causing huge economic losses to sheep and goat farming industries. Young animals are most widely affected by this disease. Several outbreaks of Orf virus disease have been reported in previous years in many provinces of China. By using the specific pathogen-free mice (C57BL/6), molecular detection (targeting the conserved region of the viral B2L gene), histopathological evaluation, and antigen localization using immunohistochemistry and immunofluorescence techniques, this study provides evidence of Orf virus detection in maternal-fetal interface tissues and fetuses that clearly depicts the possibility of transplacental transmission of Orf virus. The viral load quantification indicated the highest log copy number in maternal blood (1.1867) and placenta (1.1867), followed by amniotic fluid (0.8776), and fetal body mass (0.6146). The eosinophilic Orf viral inclusion bodies and immunostaining for Orf virus antigens were detected in the placenta and fetal tissues. Statistically, a significant difference (p < 0.05) was observed between positive and negative control groups. These findings suggest that the vertical transmission of Orf virus is possible in susceptible animals, and understanding this route might be promising in the management of the disease.