The effects of spraying on the amounts of airborne foot-and-mouth disease virus present in loose-boxes.

The air of loose-boxes which had previously held pigs infected with foot-and-mouth disease was sampled for virus after various procedures. Removal of infected pigs led to a 12- to 16-fold reduction in the amount of virus after 5 min. and a 400-fold reduction after 60 min. After heavy spraying (1.2 mm. of water in 5 min.) the amount of virus was reduced 500-fold compared to 30-fold after light spraying (0.20 mm. of water in 5 min.). The partition of infectivity associated with particle size was measured. The partition found after light spraying was similar to that found 5 min. after the pigs had been removed. Heavy spraying brought about a reduction in the infectivity associated with the large particles (> 6 mum.) but had no effect on particles less than 3 mum. A similar partition was found 60 min. after the pigs had been removed. The findings are discussed in relation to the spread of foot-and-mouth disease by the airborne route.