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

Abstract

SUMMARYThe air of loose-boxes which had previously held pigs infected with foot-andmouth 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,um.) but had no effect on particles less than 3 ,tm. 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.

Skin as a potential source of infectious foot and mouth disease aerosols

“…The measured size distribution for swine is consistent with what is known for mammalian skin cell aerosols-which are emitted in a variety of aerosol sizes but on average are large (approximately 14 mm; §2a). In addition, if the measured loosebox aerosol loss rates derived from the Sellers et al [6] and Sellers & Herniman [58] data (electronic supplementary material, table S2) are assumed to be due solely to gravitational settling, then the corresponding effective aerosol settling velocity of 0.3 m min 21 agrees well with that found for skin aerosols [10,18].…”

“…Second, the Sellers et al [6] and Sellers & Herniman [58] experiments should be repeated. These studies are unique (and therefore should be verified) because they are the only experiments identified that have examined (i) the FMDVaerosol emission rate from dead animals, (ii) the relative importance of respiratory versus non-respiratory emission pathways (suggested from the results of wholeanimal FMDVaerosol emissions from live and dead animals) and (iii) the time series of aerosol concentrations from whole animals when animals were removed from the measurement chamber (these data were used to infer the stability of infectious FMDV in natural aerosols).…”

“…Sellers et al [6] and Sellers & Herniman [58] examined the quantity of airborne FMDV in animal-holding pens (looseboxes) both prior to and after killing infected 14 Only the swine measurements are discussed in detail here as these experiments were more extensive and the FMDV signal was higher (the results for cattle also suggest a long aerosol lifetime). FMDV aerosol emissions were measured under four experimental conditions: (i) in boxes in which live swine were held, (ii) in boxes in which live swine were placed and then removed (without being killed), (iii) in boxes in which live swine were placed and then killed (bodies remained in the box), and (iv) in clean boxes in which freshly killed swine bodies were placed.…”

“…The experiments reported by Sellers et al [6] and Sellers & Herniman [58] were performed at high (greater than 90%) relative humidity. Laboratory experiments on synthetic aerosols generated from liquid FMDV suspensions have reported highhumidity aerosol decay rates that range from near zero to 1000-fold per hour, depending on the virus strain and the suspending fluid used [59 -62].…”

“…The size fractionation typically reported for fresh FMD aerosol emissions is 10 to 30 per cent in less than 3 mm, 20 to 40 per cent in 3-6 mm and 30 to 70 per cent in greater than 6 mm aerosols [5,7,48,58]. These measurements have been made in swine, and no aerosol size fractionization distribution data appear to be available for cattle or sheep emissions.…”