Newcastle disease virus (NDV) strains, isolated from outbreaks during epizootics between 1992 and 1996 in Western European countries, were compared by restriction enzyme cleavage site mapping of the fusion (F) protein gene between nucleotides 334 and 1682 and by sequence analysis between nucleotides 47 and 435. Both methods revealed that NDV strains responsible for these epizootics belong to two distinct genotypes. Strains derived from sporadic cases in Denmark, Sweden, Switzerland and Austria were classified into genotype VI [6], the same group which caused outbreaks in the Middle East and Greece in the late 1960's and in Hungary in the early 1980's. In contrast, viruses that caused epizootics in Germany, Belgium, The Netherlands, Spain and Italy could be classified into a novel genotype (provisionally termed VII), hitherto undetected in Europe. It is possible that the genotype VII viruses originated in the Far East because they showed a high genetic similarity (97%) to NDV strains isolated from Indonesia in the late 1980's.

A polymerase chain reaction combined with restriction enzyme analysis was developed for detection and differentiation of all 12 fowl adenovirus (FAdV) serotypes representing the five fowl adenovirus (A to E) species. For primer design, the published sequences of the hexon proteins of FAdV1, FAdV8 and FAdV9 were aligned and conserved regions in the two pedestal regions adjacent to the L1 loop region were determined. A primer pair (hexon A/hexon B) was constructed and was shown to amplify approximately 900 bp of the hexon gene including the L1 loop region. An amplification product was detected using supernatant of infected cell cultures from all FAdV1 to FAdV12 reference strains used in our study. The sequence and the restriction patterns of the hexon A/B fragments of the 12 FAdV strains were determined and compared. The successive use of four different endonucleases allowed the complete differentiation of the reference FAdV strains. Twenty-six fowl adenoviruses isolated during our routine virological diagnosis activities could all be amplified using hexon A/hexon B primers. Restriction analysis results showed that 8/26 adenovirus strains contained two different FAdV types. FAdV4, FAdV12, FAdV1, FAdV5 and FAdV6 were the most frequently isolated.

SUMMARYA highly virulent strain of infectious bursal disease virus (IBDV) was isolated from the field and propagated in SPF chickens, causing up to 100% mortality. Although it still belongs to the standard serotype 1 IBD viruses, serological typing with monoclonal antibodies showed an antigenic drift in this pathogenic strain. Conventional 'intermediate' IBD vaccines are probably more antigenically related to the pathogenic strain than the mild ones and were effective in protecting SPF chickens against challenge.

The sequences of the L1 loop of the hexon protein from representative fowl adenovirus (FAdV) strains of the different European and American collections were determined and compared. This study highlighted the lack of consensus in the numbering of the individual serotypes between the American and the European classifications. An identification system is proposed based on restriction fragment length polymorphism of the hexonA/hexonB polymerase chain reaction product. In addition, new insights into the relationships among FAdV strains are presented and discussed on the basis of phylogenetic analysis of the L1 loops sequences. Six clusters of strains that are supported by high bootstrap values were identified. Three of them are clearly independent, forming groups A, B and C, whereas the three others are clustered in a single 'supergroup', denominated D. Interestingly, the Japanese strain TR22 that is presently classified as European type 5 (species B) could not be assigned to any of the aforementioned clusters and might therefore constitute the sole representative of a seventh cluster.

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SUMMARYA panel of eight neutralizing monoclonal antibodies (MAbs) against the fusion (F) protein of Newcastle disease virus (NDV) has been shown to locate a major antigenic site on the basis of competitive binding assay and additivity index studies. Five epitopes (A 1 to AS) have been located within this site on the F protein of the Beaudette C strain of NDV on the basis of cross-resistance plaque assays of MAb-resistant mutants raised against these MAbs. Epitopes A1, A4 and A5 are distinct; epitope A2 partially overlaps epitope A3. Nucleotide sequence analysis of the F genes of MAbresistant mutants showed that each predicted single amino acid substitutions ranging from amino acid residues 157 to 171 for epitope A4 and at residues 72, 78, 79 and 343 for epitopes A 1, A2, A3 and A5 respectively. These locations indicate that both the F 1 and F2 fragments are involved in the formation of a single antigenic site and suggest the involvement of extensive protein folding in the active form of this F protein.

The potential of a capture enzyme-linked immunosorbent assay (ELISA) specific for chicken interferon-g (ChIFN-g) has been evaluated as a tool to assess cell-mediated immunity (CMI) in the chicken. In a first step, ChIFN-g production and cell proliferation of mitogen-activated chicken splenocytes have been compared. In general, for each of the stimulation conditions where significant proliferation was observed, production of ChIFN-g could be measured by ELISA. In our hands, the combination of ionomycin and phorbol-12-myristate 13-acetate or the use of recombinant chicken interleukin-2 gave the most satisfactory results. Then, the CMI response induced by live or killed Newcastle disease virus (NDV) vaccines has been evaluated sequentially by ex vivo antigen-specific ChIFN-g production and cell proliferation of splenocytes from immune chickens. The ex vivo data showed that both types of NDV vaccines are capable of stimulating CMI responses to NDV in chickens as measured by the ChIFN-g ELISA. However, most of the chickens vaccinated with the live vaccine produced ChIFN-g after antigen recall stimulation, from 2 to 4 weeks after vaccination, when only some chickens vaccinated with the inactivated vaccine showed a specific response 4 weeks after vaccination. No significant proliferative responses to either NDV vaccine were detectable during the 4 weeks of the study. From our results, it appears that antigen-specific ChIFN-g production can be used as a good indicator of actively acquired immunity to NDV and that the sensitivity range of the capture ELISA test is well adequate to measure ex vivo release of ChIFN-g.

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