Virus particles and antigens in experimental orf scabs

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

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.

Microbiological research at the Centre for Tropical Veterinary Medicine (CTVM)

The nature of the research carried out by the staff of the Microbiology Section of the Centre for Tropical Veterinary Medicine (CTVM) at home and abroad is illustrated by precis of projects on rinderpest, orf in goats and sheep, bovine dermatophilosis, contagious caprine pleuropneumonia, tick-borne fever in goats and sheep, bovine petechial fever, and caprine cowdriosis.

Sero-surveillance for orf antibodies in sheep and goats in Saudi Arabia employing the ELISA technique

A serological survey was conducted on sheep and goats in Saudi Arabia to detect humoral antibodies against the orf virus. The ELISA technique was superior to the AGID and CFT in detecting such antibodies. Of the 239 abattoir serum samples examined, 60 per cent had orf antibodies by ELISA while 94.8 per cent of the convalescent sera had antibodies detectable by ELISA. With the lack of vaccination and the reports that the clinical disease is commonly seen in different parts of the Kingdom, it may be that orf is becoming enzootic in this country. Recommendations for implementing a satisfactory vaccination regimen are given.