Antibody detection-based differential ELISA for NDV-infected or vaccinatedchickens versus NDV HN-subunit vaccinated chickens

With the advent of subunit vaccines for microbial diseases it is becoming i ncreasingly important to be able to differentiate naturally infected animal s from those vaccinated with the corresponding subunit vaccine. For avian v iruses such as Newcastle disease virus (NDV), a whole virus-based ELISA can not make such a differential diagnosis since in both cases the antisera wou ld react with the whole virus. The nucleocapsid protein (NP) gene of the ND V Hitchner B1 strain was cloned, sequenced and expressed to develop a diffe rential ELISA. The B1 NP had 95.7 and 96.1% amino acid identities with the MP of the d26 and Ulster 2C strains, respectively. The B1 NP expressed in a baculovirus expression vector (recNP) was the expected size and reacted wi th NDV-specific antibodies (Ab) in Western blots and by radioimmunoprecipit ation. The ELISA using recNP-coated wells, tested on serum samples from flo cks pretested with a commercial NDV kit gave results corresponding to those of the kit. Furthermore, use of both the recNP-based ELISA and a whole vir us ELISA allowed the differentiation of birds vaccinated with a NDV haemagg lutinin-neuraminidase (HN) expressing fowlpox virus from birds infected wit h NDV. This provides the basis for establishing an ELISA that discriminates between the antibody response to a recombinant fowlpox vaccine (expressing NDV HN protein) and that to live and inactivated NDV. (C) 1999 Elsevier Sc ience B.V. All rights reserved.