Development and preliminary validation of an ad hoc N1-N3 discriminatory test for the control of avian influenza in Italy.

The development of a discriminatory test, based on the differentiation between N1 and N3 antibodies, to be used in the framework of a vaccination program, based on vaccination with a heterologous H7N3 inactivated vaccine against the Italian H7N1 field virus, is reported. The indirect immunofluorescence antibody (iIFA) assay was based on the expression of the N1 protein in a baculovirus system. HighFive insect cells were transfected with the recombinant virus and used as an antigen in the iIFA test. Preliminary validation on 608 turkey sera yielded relative sensitivity and specificity of 98.1% and 95.7%, respectively, when compared to the HI test with an almost perfect agreement between the two methods (Kappa value = 0.93). It is concluded that the iIFA test is a valid tool for monitoring avian influenza infection in a vaccinated population.