Characterization of orthopoxviruses isolated from feline infections in Britain

The biological properties and genomes of orthopoxviruses isolated from cats in Britain were compared with strains of cowpox virus isolated from cows and their handlers. All the isolates tested produced haemorrhagic pocks and A-type inclusions on the CAM, but did not produce pocks above 40 degrees C. Thus the feline isolates behaved as typical strains of cowpox virus. Differences were found in the heat resistance of the virions and in the character of the A-type inclusion which did not correlate with the host from which the viruses were isolated. Analysis of the genomes with a variety of restriction endonucleases showed very close relationship between all the isolates and also failed to separate feline isolates from cowpox virus. However again minor differences, which may prove to be of epidemiological value were detected. We conclude that the orthopoxvirus currently isolated from domestic cats in Britain is cowpox virus and that there is no evidence that a feline variant or subspecies circulates in Britain.