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Bulletin No. 21 - Spring 2005
VirologyInternational Society for Animal Hygiene ? Saint-Malo - 2004
VAN REETH K, LABARQUE G, PENSAERT M
Seroprevalence of swine influenza in Europe and interpretation of serological findings.
Proceedings of the International Society for Animal Hygiene, 2004, 323-324
Currently, three subtypes of swine influenza virus (SIV) circulate in Europe, namely H1N1, H3N2 and the more recent H1N2. This paper reports the results of a serological survey carried out within the framework of the "European Surveillance Network for Influenza in Pigs" (ESNIP). The 4377 serum samples included in this survey were collected in SIV-non-vaccinated pigs from 12 out of the 19 main swine production regions in Europe. All samples were tested by hemagglutination inhibition (HI) for all three subtypes. In countries with low SIV prevalence H1N1 results the dominant subtype. The infection with more than one subtype is commonly found in sows and fattening pigs, but sows results more frequently positive to all three subtypes than fattening pigs, probably due to their longer lifetime. Then the authors move on to some aspects of SIV serology. A reliable HI test should be designed with at least one recent representative of each of the three subtypes. Low titers (1:10 or 1:20) should not be considered as resulting from non-specific inhibition since a rapid decline of antibody titers after infection can occur. Two serum samples are necessary to establish SIV infection: the first one collected during the acute phase (low or no HI antibody titers) and the other one collected during the chronic phase (significant rise of HI antibody titers), keeping in mind that the serological response to a given subtype will be modified in pigs with antibodies to other subtypes (booster effect) compared to that of fully seronegative pigs. To achieve a suitable overview of the immune status of a non-vaccinated herd, it is recommended to test 10 fattening pigs, 15 sows and 10 suckling piglets. In a vaccinated herd (H1N1 and H3N2 subtypes), sows have usually higher HI antibody titers and are more subjected to serological cross-reaction.
