Sites of release of airborne foot-and-mouth disease virus from infected pigs.

Pigs infected with foot-and-mouth disease virus by different routes of exposure were air-sampled individually, first as 'intact' (I-) pigs and then as 'intubated' (T-) pigs, using an endotracheal tube. Irrespective of the route of infection it was found that during the early stages of disease more virus was recovered from I-pigs than from T-pigs. Most of the virus from I-pigs during incubation and early disease was associated with large and medium sized particles. T-pigs infected by direct or indirect contact excreted a range of particle sizes at this time but T-pigs infected by inoculation only excreted small particles. During advanced disease all sizes of particle were excreted by I- and T-pigs. Greater amount of airborne virus were recovered at this time from I-pigs than T-pigs infected by indirect contact but I-pigs infected by intravenous or intradermal inoculation excreted less infectivity than T-pigs. The results show that the respiratory tract is involved during the early stages of foot-and-mouth disease in pigs infected by either natural or experimental routes of exposure and suggest that upper respiratory infection precedes lower.