Vertical transmission of Orf virus in goats and its prevention

Contagious ecthyma dermatitis, caused by Orf virus (ORFV), is an important zoonotic disease of small ruminants, particularly goats and sheep, and can occasionally infect humans. The morbidity of the disease is high in newborn kids or lambs as compared with adult animals, even leading to death in severe cases due to emaciation or secondary infections. Despite its significance, the precise route of ORFV transmission to newborn kids or lambs has remained unclear. In this study, we hypothesized that ORFV may be transmitted transplacentally from dam to fetus and investigated the presence of the virus in maternal-fetal interface tissues. Molecular detection targeting the ORFV B2L gene provided evidence supporting vertical transmission. The average viral loads in placental cotyledons and umbilical cords were 10^4.25 copies/mg and 10^3.50 copies/mg, respectively. Furthermore, vaccination of pregnant goats significantly reduced the vertical transmission rate of ORFV, with the ORFV-positive rate decreasing from 90.0% in non-vaccinated dams to 56.14% in vaccinated dams, from 71.43% to 14.29% in umbilical cord blood, and from 36.67% to 0% in kids born to vaccinated dams. Collectively, these findings identify vertical transmission as an important, previously under-recognized route of ORFV infection and highlight the importance of maternal vaccination in mitigating infection risk among newborn kids or lambs.