Potency of a recombinant NDV-H5 vaccine against various HPAI H5N1 virus challenges in SPF chickens.

For the past decade, several recombinant Newcastle disease viruses (rNDV) have been used as a vector to express native or modified avian influenza (AI) hemagglutinins (HA) in order to give preventive protection against highly pathogenic avian influenza (HPAI) H5N1 viruses. Obtained protections were dependent on the age of the chickens, on the constructs and, in particular, on the homology between the HA that was inserted and the challenge strains. The objective of this study was to investigate the vaccine efficacy of a recombinant NDV La Sota-vectored vaccine expressing an Asian clade 1 H5 ectodomain (rNDV-H5) vaccine expressing a modified H5 ectodomain from an HPAI clade 1 H5N1 isolate as vaccine for 1-day-old specific-pathogen-free chickens. The inoculation route (oculonasal vs. drinking water), the dose-effect, and the protective range of this rNDV-H5 vaccine were studied. Both routes of vaccination induced an H5 serologic response and afforded a high degree of clinical protection against an Asian clade 1 HPAI H5N1 (AsH5N1) challenge without a significant difference between inoculation routes. A clear dose-effect could be demonstrated. Furthermore, when evaluating the protective range against antigenically divergent descendants of the Asian dade 1 HPAI H5N1 lineage, namely two Egyptian clade 2.2.1 H5N1 strains, the vaccine efficacy was less satisfactory. The rNDV-H5 vaccine provided good clinical protection and reduced viral shedding against Egyptian 2007 challenge but was unable to provide a similar protection against the more antigenically divergent Egyptian 2008 strain.

A chemically defined production process for highly attenuated poxviruses.

Highly attenuated poxviruses are promising vectors for protective and therapeutic vaccines. These vectors do not replicate in human cells and can therefore be safely given even to immunocompromised recipients. They can accommodate very large inserts and provide strong stimulation of the immune system against the vectored antigen. Disadvantages include that very high numbers of infectious units are required per dose for full efficacy. Because they are difficult to produce, improved cellular substrates and processes are urgently needed to facilitate programs intended to reach a large number of vaccinees. We have developed a fully scalable and very efficient chemically-defined production process for modified vaccinia Ankara (MVA), canarypox (CNPV, strain ALVAC) and fowlpox viruses (FPV) based on a continuous cell line.

A field study on the significance of vaccination against infectious bursal disease virus (IBDV) at the optimal time point in broiler flocks with maternally derived IBDV antibodies.

The right strategy for infectious bursal disease (IBD) control and its success rate under field conditions depends on hygiene management, IBD field pressure, level and variation in maternally derived IBD antibodies, and the IBD vaccine strains to be used. Usually, standard vaccination programmes are used, which are not always adapted to the specific conditions on the farm and to the immune status of chickens. Employing the "Deventer formula" may help to estimate the optimal time for vaccination for a specific flock based on the maternally derived antibody level, its variation, the genetic background of the chicken, and the IBD vaccine strain. Two field studies with 16 or 20 commercial broiler flocks were conducted, applying an intermediate IBD vaccine before, at the best, and after the estimated optimal vaccination time estimated by the "Deventer formula". These studies showed that flocks IBD-vaccinated between 1 day before, at, or up to 3 days after the estimated optimal time point developed detectable humoral immunity up to 14 days post vaccination. If birds had been vaccinated more than 1 day before the calculated optimal vaccination date, the humoral immune response was delayed or non-detectable until slaughter. The induction of humoral immunity correlated with the incidence of bursa lesions and IBDV detection by reverse transcriptase-polymerase chain reaction. As indicated in this study, under field conditions bursa lesions may develop later than predicted based on experimental experiences. The late incidence of bursa lesions after vaccination may be confused with field virus-induced lesions, in which case sequencing may offer a valuable tool for differentiation.

Characterization of duck leucocytes by monoclonal antibodies.

cDNAs encoding CD3epsilon, CD4 and the alpha-chain of CD8 of ducks were cloned. Monoclonal antibodies against Pekin duck CD4 and CD8alpha revealed that the antigens were expressed by the majority of thymocytes and by subpopulations of CD3+ cells in peripheral tissues. CD8alpha cell surface expression was also found on 90% of bursal cells. The B cell specificity of a newly developed mab to the immunoglobulin light-chain (L-chain) was confirmed by double labelling studies with the chicken B-cell cytokine BAFF. Using these tools and a mab reacting with the cytoplasmic domain of CD3epsilon, we demonstrated that the CD8alpha molecule is expressed to high levels in CD3-positive T cells and at lower levels in CD3-negative bursal and peripheral B cells. Mab 2-4, which recognizes the chicken CD28 molecule, was found to react with CD4-positive duck lymphocytes and with CD8-positive duck T cells but not with CD8-positive B cells. Mab K1, which recognizes a common antigen on chicken thrombocytes and monocytes/macrophages, was found to react with duck thrombocytes and macrophages. Thus, a range of mabs is now available which will allow to phenotype the major leucocyte populations in ducks, a surrogate infection model for hepatitis B virus.

Performance of enzyme-linked immunosorbent assays for detection of antibodies against T. congolense and T. vivax in goats.

Indirect ELISAs using denatured antigen preparations of Trypanosoma (T.) congolense (TcAGd) and T. vivax (TvAGd) for detection of anti-trypanosome antibodies in bovine serum (I-TAB ELISAs), were adapted for serodiagnosis in goats. The diagnostic proficiency, the cross-reactivity with sera from heterologous trypanosome infections and the operational performance of the assays were evaluated on experimentally trypanosome-infected goats. The I-TAB ELISA (TcAGd) detected antibodies in all T. congolense infected goats (100% overall sensitivity) from 2 to 4 weeks post-infection (p.i.) until the end of the experiments. Specificity tested on 92 uninfected goats was 96.7%. Extensive cross-reactions of I-TAB ELISA (TcAGd) with sera from T. vivax or T. brucei infected goats were observed. The I-TAB ELISA (TvAGd) detected antibodies in 5 of the 6 T. vivax infected goats, specificity tested on uninfected goats was 100%. Cross-reactivity with sera from T. congolense or T. brucei infected goats remained limited. Infecting species identification based on the highest percent positivity (PP) in both systems, correctly identified all T. congolense infections, but misidentified in 2/19 occasions a T. vivax infection as a T. congolense infection. In the absence of T. brucei specific antigen coated plates, T. brucei infections were identified in, respectively, 7/9 and 2/9 occasions as T. congolense or T. vivax infections. Acceptable inter-plate repeatability was observed. The implications of results and technical requirements for ongoing applied research are discussed.