Survival of orf virus under British winter conditions.
Scabs collected from experimentally induced orf (contagious ecthyma) were subjected to five test conditions from November 1984 to May 1985, after which the infectivity was tested in susceptible lambs. The scabs were ground in sterile sand and maintained at -20°C, 4°C or 18°C, or were fixed to fresh turf outdoors with a covering of plastic or just a wire mesh to prevent interference from birds. During the period there were 497 h of sunshine, 18 days of snow lying, 292 mm of rain; 16.2°C was the maximum and - 7.5°C the minimum air temperature. Histological lesions of orf were produced by samples under each of the test conditions apart from complete exposure outdoors. The major factor in inactivation of the virus seemed to be exposure to rain. The virus was unlikely to survive for long in exposed areas in the UK.