Airborne excretion of foot-and-mouth disease virus

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Abstract
A large-volume sampler was used to recover virus excreted as aerosol by cattle, sheep and pigs infected with foot-and-mouth disease. Pigs were found to excrete virus to a maximum of 104.7 ID 50 per animal per hour and sheep and cattle to a maximum of 103.2 ID 50. Excretion from pigs totalled 106 ID 50 per animal over 5 days and from cattle and sheep 3 x 104 ID 50 per animal over 4 days. Maximum recovery occurred 41 hr. after infection in pigs and cattle when lesions had generalized and 17 hr. after infection in sheep before lesions had been observed. Sampling in a multistage liquid impinger showed that 65–71% of virus was excreted as an aerosol of size > 6 μ, 19–24% 3–6 μ and 10–11% less than 3 μ. The site of production of virus excreted as aerosol is suggested to be the upper respiratory tract. Under conditions of relative humidity greater than 70% and at low temperatures, survival of virus to a distance of 100 km. is likely to occur and because of the minute respiratory volume the aerosol would be sampled more efficiently by cattle than pigs or sheep and by large animals than by small. These findings are discussed in relation to spread of virus in the field.Mr Dave Allen and Massey-Ferguson Ltd. are thanked for their generous donations, with which the large-volume sampler was purchased. We are grateful to Dr C. E. Gordon Smith, Mr G. J. Harper and Dr K. P. Norris of the Microbiological Research Establishment, Porton, for advice and help and for the loan of the multistage liquid impinger. The technical assistance of N. H. Cheale and C. W. Hawkins is gratefully acknowledged.