Studies on respiratory diseases of pigs. IV. Transmission of infectious pneumonia and its differentiation from swine influenza.

Abstract

Attempts were made to isolate new strains of swine influenza viruses from outbreaks of respiratory diseases in pigs. The material used was obtained from outbreaks in East Anglia and in Northern Ireland. In addition, the lungs of pigs showing consolidation were obtained from a bacon factory and some lungs were collected at local slaughter houses. A good many of the lungs used were bacteriologically sterile. Sometimes pigs alone were inoculated, but in most cases ferrets, mice and developing chick embryos were also inoculated. Transmission experiments with bacteria-free filtrates of lung suspensions indicated the presence of a filterable agent in several specimens, but the clinical symptoms in pigs thus inoculated differed considerably from those produced by inoculation of swine influenza virus, and no antibodies were produced against the latter virus. No virus was isolated in chick embryos, ferrets or mice. These observations suggest that swine influenza is not prevalent at present in the United Kingdom and that the form of infectious pneumonia which is most common is due to a virus different from swine influenza. This disease appears to be widespread and needs further study.