Natural transmission of orf virus from clinically normal ewes to orf‐naive sheep

Abstract

The apparent natural transmission of orf virus from clinically normal ewes to susceptible sheep was observed during a border disease vaccine experiment. The 14 susceptible sheep were persistently infected with border disease virus and had been reared indoors in isolation from other sheep since birth. Their ages ranged from two to four years and they were housed in two groups; group 1 consisted of four sheep persistently infected with the Moredun strain of border disease virus and group 2 consisted of 10 sheep persistently infected with the Oban strain of the virus. On day 0, six sheep were removed from group 2 and rehoused. To the remaining four sheep in each group were added eight four- to six-year-old pregnant conventionally reared ewes at 48 days gestation. Fourteen days later the four sheep in group 1 were moved to another pen housing eight similar five-year-old pregnant ewes at 48 days' gestation, and the four sheep from group 2 were rehoused with their original stallmates. Twenty-one days later lip lesions typical of orf were first observed on the sheep from both groups and the disease spread to all the sheep persistently infected with border disease virus over the next four weeks. Virological and serological evidence demonstrated that the source of infection for the sheep was almost certainly the conventionally reared ewes, on which no lesions resembling orf were observed at any time during the study.

A Nuclear Inhibitor of NF-κB Encoded by a Poxvirus

“…Therefore, deletion of single poxviral NF-B inhibitors may be complemented to some extent by the action(s) of other inhibitors, thus masking potential effects on virus virulence and pathogenesis. Alternatively, ORFV NF-B inhibitors may play roles in less understood aspects of ORFV biology, such as subclinical/persistent infections (26,37), favoring virus replication and transmission in the absence of overt viral infection.…”

Severe Persistent Case of Contagious Ecthyma (Orf) in Goats

“…Persistent infections with severe, generalized skin proliferative lesions have been reported; (De La Concha-Bermejillo et al, 2003). Persistently infected carrier goats and sheep have been demonstrated to be the main source of disease and infection in the farm that can relapse during time of stress (Nettleton et al, 1996). Exposure of animals to stress or infection can accentuate the severity of the disease.…”

Orf in Goats in China: Prevalence and Risk Factors

“…This finding suggests that the prevalence of orf may be underestimated, because no clinical symptoms have been observed in subclinically infected animals. Subclinical ORFV infection indeed occurs, because ORFV can transmit from clinically normal ewes to susceptible sheep and may serve as a source for new outbreaks, because fatal orf in lambs following long distance transportation has been reported [4,25]. However, a relatively low positive rate in swabs could be explained by the fact that ORFV is not detectable 30 d after challenge in either newly regenerated epidermis or the remnants of surface scabs, although it is present in scabs overlying healing lesions by day 20 [1].…”