Airborne excretion of foot-and-mouth disease virus

Abstract

Foot-and-mouth disease (FMD) virus may spread in a number of ways: by direct contact between infected and susceptible animals, by animal products such as meat and milk, by mechanical transfer on people, non-susceptible animals, birds, vehicles and fomites, and by the airborne route. The initial pattern of outbreaks at the beginning of the epidemic in the West Midlands of England in 1967 suggested that spread was airborne. The meteorological evidence for this and for past epidemics in Great Britain has been investigated by L. P. Smith, P. B. Wright and M. Hugh-Jones (personal communications, 1968-9) and by Hurst (1968). Henderson (1969) has also studied the spread of disease in the Worcestershire area and attributed much of it to wind carriage. Methods and results of aerosol sampling of virus and infected cattle were reported by Thorne & Burrows (1960) and by Hyslop (1965). In this paper the results are given of the measurement of virus in aerosols produced by cattle, sheep and pigs infected with FMD virus.

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

“…the development of visible lesions outside the inoculation site)-the time when FMDV skin concentrations peak. Emissions then persist for several days [1,5,7,48,49]. While this may generally be the case, airborne FMD has occasionally been observed to begin on the day before clinical signs appear or alternatively to begin as much as several days after the development of clinically evident lesions.…”

“…The rupture of these macroscopic skin lesions, with the subsequent release of FMDV-infected cell cytoplasm onto the surface of the skin followed by exfoliation of the infected skin cells, is one pathway whereby FMDV could become aerosolized 7 (i.e. FMDV 'rafting' on the outside of airborne skin cells) [37,42,45].…”

“…However, a general association of FMDV aerosol emissions with clinical skin lesion development is particularly strong in the swine experiments in which infection occurred via airborne or direct contact. 10 In these experiments, most animals emitted no airborne virus prior to skin lesion development and no airborne emissions were reported more than 1 day prior to the development of the clinical signs of FMD [5,7,50].…”

“…Early researchers did previously raise the possibility that airborne FMDV-infected skin cells might be important in disease transmission [6][7][8]; however, this possibility was never systematically investigated. In contrast, respiratory mucosal epithelial cells are known to be a primary site of initial infection (pharynx), a main virus amplification site (mouth) and the site of persistent infection in carrier ruminants (pharynx) [1,9].…”

Pathogenesis of foot-and-mouth disease: the lung as an additional portal of entry of the virus

“…Earlier we presented a working hypothesis for the pathogenesis of FMD in which the upper respiratory tract was considered as the portal of entry for the virus. The present results require revision of this hypothesis to include the role of the lung, particularly because a substantial amount of evidence has established the importance of airborne transmission of FMD (Donaldson, Herniman, Parker & Sellers, 1970;Hyslop, 1965;Sellers & Parker, 1969, Sellers, Donaldson & Herniman, 1970Sellers et al 1973). FMD-infected animals generate aerosols with various droplet sizes (Sellers & Parker, 1969), and recipient animals will be exposed to all of them.…”