The demonstration by interference tests of an infective agent in fetuses from ewes inoculated with Border disease tissue.

Fetuses and placental tissues were taken from pregnant ewes at intervals varying between eight and 21 days after inoculation with tissue suspensions from cases of Border disease. Virus isolation procedures involving the detection of a cytopathic effect in tissue cultures with or without interference tests produced universally negative results but interference tests, using a plaque technique with the NADL strain of bovine virus diarrhoea virus as a challenge virus, detected the presence of an agent in tissues from six out of 10 fetuses. Inoculated ewes allowed to proceed to term showed a serological response characteristic of Border disease infection, as measured by four different tests. Although hairy shaker lambs were not seen, the occurence of abortion and stillbirth due to causes other than bacterial agents, was an indication that the Border disease agent was present. Electron microscopy of fetal fluids failed to detect viral particles.