A comparison of DNA proffles of representative isolates of orf virus, obtained using four different restriction endonucleases (RE), showed that the enzyme EcoRi could be used to discriminate between wild-type virus isolates and vaccine strains. The enzyme was used to compare the RE profres of orf virus isolates from 43 outbreaks of orf that occurred in vaccinated flocks between 1988 and 1993; 21 outbreaks yielded wild-type virus, 10 yielded vaccine viruses, three produced both vaccine and wild-type viruses and no clear result was obtained from nine of the outbreaks. From the 21 outbreaks yielding wildtype viruses, 28 orf virus isolates had clear RE profiles and 15 distinct RE profiles were recorded. Usually only one virus type was associated with each outbreak but from two farms, two different wild-type viruses were recovered. No predominant genotype was identified, with four RE profile types being recovered for more than one outbreak. From the more severe form of orf involving the buccal cavities of lambs only wildtype viruses were recovered, with at least four different genotypes being represented.
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↵Mr Lewis' present address is Veterinary Laboratories Agency, Veterinary Investigation Centre, Kendal Road, Harlescott, Shrewsbury SY2 4HD
↵Ms Stephens' present address is Institute for Animal Health, Compton, Newbury, Berkshire RG20 7NN
↵Mr Madeley's present address is J. M. Consultancy, The Glen, 46 Amersham Hill Drive, High Wycombe, Buckinghamshire HP13 6QY