Influenza in swine in Belgium (1969-1986): epizootiologic aspects

From 1984 until 1986, influenza isolates were obtained from 59 outbreaks of respiratory tract disease in Belgium. In 21 of the outbreaks, H3N2-influenza virus isolates, related to the human A/Port Chalmers/1/73 strain were obtained. All other isolates were H1N1-influenza virus strains. The prevalence of variants of the human H3N2-influenza virus in the Belgium swine population was determined by examining sow sera which had been collected between 1969 and 1984. The results of this serological study showed that, although a Port Chalmers-like strain was associated with outbreaks of respiratory tract disease in swine only since 1984, such strain was already present in the swine population in 1974, when a low percentage of sow sera (7%) reacted with A/Port Chalmers/1/73. Between 1975 and 1984, antibody against this strain were present in 28-61% of the sera. Furthermore, 3-6% of the sera collected between 1971 and 1980 reacted with the A/Hong Kong/1/68 strain. There were no indications that more recent human H3N2-strains (A/Texas/1/77, A/Bangkok/1/79 and A/Belgium/2/81) circulated in the Belgian swine population.