SEROLOGICAL STUDIES OF INFLUENZA-VIRUSES IN PIGS IN GREAT-BRITAIN 1991-2

Samples from a sow serum bank representative of the pig population of Great Britain collected during 1991-2, were examined for antibodies to influenza A, B and C viruses, using viruses which had been isolated f rom a variety of hosts. For influenza-A viruses there was evidence of the continued circulation of classical swine' H1N1 virus (26 %) seropr evalence), and human H3N2 viruses (39 %) which are antigenically most closely-related to A/Port Chalmers/1/73 virus. In addition antibodies were detected to A/swine/England/201635/92 (8 %), a strain of H3N2 vir us which appears to have arisen by antigenic drift from conventional H 3N2 swine strains. Specific antibodies (2%) were detected to an H1N1. virus (A/swine/England/195852/99) related most closely to avian H1N1 s trains. In tests with human H1N1 and H3N2 viruses, excluding isolates from pigs, the highest seroprevalence was detected to the prevailing s trains from the human population. Serological tests with avian H4 and H10, human H2, equine 1 and 2 influenza A viruses were all negative. S even pigs seropositive by haemagglutination-inhibition, virus neutrali zation and immunoblotting assays for antibody to influenza B virus, we re randomly distributed geographically suggesting that influenza B vir uses may be transmitted to pigs but fail to spread. The seroprevalence to influenza C viruses was 9.9 % indicating that these viruses are wi despread in pigs. These results provide further evidence that the pig: can be infected by a number of influenza viruses, some of which may h ave significance in the epidemiology of human influenza.