Swine Influenza Virus: Validation of the ID Screen Influenza A Antibody Competition ELISA

the HI assay can be influenced by non-specific serum inhibitors the reactivity of both HI and SN assays strongly depends on the test virus strain used (homologous or heterologous strains) 1 . HI titers show a peak 2-3 weeks after experimental infection. After a maximum of 22 weeks, these titers decrease and become negative, while ELISA still may give positive resultats 3 . Indirect ELISAs seem to be specific, but are known to lack sensitivity 1,2,4,5 . Poor correlations in indirect H1N1 and H3N2 ELISAs may be due to antigenic differences between (1) the strains used in the test kits and (2) European H1N1 and H3N2 SIV strains 2 . Discrepancies between HI and indirect ELISA results may also be due to differences in antibody isotypes detected by each test. Indirect ELISA mainly detect IgG antibodies, whereas the HI test detects both IgM and IgG 5 antibodies.