Seroprevalence of antibodies against swine influenza virus in pigs of different age

The prevalence of antibodies specific to swine influenza virus (SIV) among domestic pigs of different age, raised in large farms in Poland and Lithuania, was evidenced. Two thousand seven hundred and thirty five blood samples, taken from non-vaccinated animals were tested in HI assay against 3 SIV strains (H1N1, H1N2 and H3N2 subtypes). As a positive result the haemagglutinin titre >= 20 was estimated. Performed monitoring study showed that the most spread is H IN 1 subtype of SIV. The occurrence of antibodies specific to SIV depended on the age of the tested animals. The first parity sows in Poland had low level of antibodies against H1N1 subtype (about 8%, at both - farm and individual levels) and no antibodies against H1N2 or human variant of SIV. In Lithuania, first parity sows presented the antibodies against H1N1 (27.3% of farms) and H1N2 (9.1% of farms) subtypes. The percentage of seroconversion among individual sows reached in this country 1.1 and 0.8 for H1N1 and H1N2 subtypes, respectively. It should be stressed that no antibodies against any of the tested subtypes of SIV were detected in boars and suckling piglets. The highest percentage of animals producing antibodies to all 3 antigens was detected, in both countries, among weaners and fatteners. In Poland it reached the level 11.1, 5.5, and 2.8 while in Lithuania - 18.2, 9.1, and 0, respectively against H1N1, H1N2 and H3N2 subtypes. The titre of the sera ranged from 20 to 160, but in the most samples it was low.