A N T I G E N I C RELATIONSHIP OF BRITISH SWINE INFLUENZA STRAINS TO STANDARD HUMAN AND SWINE INFLUENZA VIRUSES* Tm~ USE OF CmCtCES AND F~RP.ET ANTISERA IN RED CELL AGGLUTINATION

The antigenic relationships of strains of the human and swine influenza viruses have presented a puzzling problem for investigation. Soon after studies on this subject were undertaken, it became evident that some of the apparent antigenic differences determined by a variety of methods were not significant. The differences were considered to be quantitative rather than qualitative, which led to the inclusion of numerous human strains in one group designated as Type A (1). As other strains from man were isolated, they were either included in the accepted Type A group or, on the basis of distinct antigenicity, placed in another category (Type B) with other strains of like antigenic nature. Swine influenza in the United States was first described by Dorset, McBryde, and Niles (2) in 1922, and its specific virus was isolated by Shope (3) in 1931. A similar disease has been recognized clinically in Great Britain and on the Continent for some years. Although clinical, pathological, and contributing bacterial factors are different in the disease as it occurs in America and in Europe, virus has been demonstrated in outbreaks abroad having properties much like the strains of swine influenza virus of American origin. A survey of the situation, under the title of "Piglet influenza or infectious pneumonia~" has been published by Lamont (4). From epizootics in swine of North Ireland and of Cambridge, England, virus strains have been isolated by Lamont and Shank (4), Blakemore and Gledhill (5), and Glover and Andrewes (6). The work to be reported here on swine viruses from Cambridge and North Ireland is a continuation of studies undertaken in 1940-41 by one of us with Dr. R. E. Glover and Dr: C. H. Andrewes, at the National Institute for Medical Research, London.