Pathogen-free White Leghorn Chickens Research Articles

Protective Efficacy of H9N2 Avian Influenza Vaccines Inactivated by Ionizing Radiation Methods Administered by the Parenteral or Mucosal Routes.

H9N2 viruses have become, over the last 20 years, one of the most diffused poultry pathogens and have reached a level of endemicity in several countries. Attempts to control the spread and reduce the circulation of H9N2 have relied mainly on vaccination in endemic countries. However, the high level of adaptation to poultry, testified by low minimum infectious doses, replication to high titers, and high transmissibility, has severely hampered the results of vaccination campaigns. Commercially available vaccines have demonstrated high efficacy in protecting against clinical disease, but variable results have also been observed in reducing the level of replication and viral shedding in domestic poultry species. Antigenic drift and increased chances of zoonotic infections are the results of incomplete protection offered by the currently available vaccines, of which the vast majority are based on formalin-inactivated whole virus antigens. In our work, we evaluated experimental vaccines based on an H9N2 virus, inactivated by irradiation treatment, in reducing viral shedding upon different challenge doses and compared their efficacy with formalin-inactivated vaccines. Moreover, we evaluated mucosal delivery of inactivated antigens as an alternative route to subcutaneous and intramuscular vaccination. The results showed complete protection and prevention of replication in subcutaneously vaccinated Specific Pathogen Free White Leghorn chickens at low-to-intermediate challenge doses but a limited reduction of shedding at a high challenge dose. Mucosally vaccinated chickens showed a more variable response to experimental infection at all tested challenge doses and the main effect of vaccination attained the reduction of infected birds in the early phase of infection. Concerning mucosal vaccination, the irradiated vaccine was the only one affording complete protection from infection at the lowest challenge dose. Vaccine formulations based on H9N2 inactivated by irradiation demonstrated a potential for better performances than vaccines based on the formalin-inactivated antigen in terms of reduction of shedding and prevention of infection.

Combination of TLR2 and TLR3 agonists derepress infectious bursal disease virus vaccine-induced immunosuppression in the chicken

Live intermediate plus infectious bursal disease virus (IBDV) vaccines (hot vaccines) are used for protection against the virulent IBDV strains in young chickens. We evaluated the potential of Toll-like receptor (TLR) agonists to alleviate hot vaccine-induced immunosuppression. The combination of Pam3CSK4 and poly I:C synergistically upregulated IFN-β, IFN-γ, IL-12, IL-4, and IL-13 transcripts and cross-inhibited IL-1β, IL-10, and iNOS transcripts in the chicken peripheral blood mononuclear cells (PBMCs) as analyzed by quantitative real-time PCR. Further, four-week old specific pathogen free White Leghorn chickens (n = 60) were randomly divided into six groups and either immunized with hot IBDV vaccine with or without Pam3CSK4 and/or poly I:C or not vaccinated to serve as controls. The results indicated that poly I:C alone and in combination with Pam3CSK4 alleviated vaccine-induced immunosuppression, as evidenced by greater weight gain, increased overall antibody responses to both sheep erythrocytes and live infectious bronchitis virus vaccine, upregulated IFN-γ transcripts and nitric oxide production by PBMCs (P < 0.05), and lower bursal lesion score in the experimental birds. In conclusion, poly I:C alone and its combination with Pam3CSK4 reduced the destruction of B cells as well as bursal damage with restoration of function of T cells and macrophages when used with a hot IBDV vaccine.

Experimental challenge of chicken vaccinated with commercially available H5 vaccines reveals loss of protection to some highly pathogenic avian influenza H5N1 strains circulating in Hong Kong/China

Highly pathogenic avian influenza (HPAI) H5N1 virus continues to circulate in poultry in Asia and Africa posing a threat to both public and animal health. Vaccination, used as an adjunct to improved bio-security and stamping-out policies, contributed to protecting poultry in Hong Kong from HPAI H5N1 infection in 2004–2008 although the virus was repeatedly detected in dead wild birds. The detection of clade 2.3.4 H5N1 viruses in poultry markets and a farm in Hong Kong in 2008 raised the question whether this virus has changed to evade protection from the H5 vaccines in use. We tested the efficacy of three commercial vaccines (Nobilis, Poulvac and Harbin Re-5 vaccine) in specific pathogen free white leghorn chickens against a challenge with A/chicken/Hong Kong/8825-2/2008 (clade 2.3.4) isolated from vaccinated poultry in Hong Kong and A/chicken/Hong Kong/782/2009 (clade 2.3.2). Harbin Re5 vaccine provided the best, albeit not complete protection against challenge with the clade 2.3.4 virus. All three vaccines provided good protection from death and significantly reduced virus shedding following challenge with the clade 2.3.2 virus. Only Harbin Re-5 was able to completely protect chickens from virus shedding as well as mortality. Sera from vaccinated chickens had lower geometric hemagglutination inhibition titers against A/chicken/Hong Kong/8825-2/08, as compared to two other clade 2.3.4 and one clade 0 virus. Alignment of amino-acid sequences of the haemagglutinin of A/chicken/Hong Kong/8825-2/08 and the other H5 viruses revealed several mutations in positions including 69, 71, 83, 95, 133,140, 162, 183, 189, 194 and 270 (H5 numbering) which may correlate with loss of vaccine protection. Our results indicated that the tested HPAI H5N1 (2.3.4) virus has undergone antigenic changes that allow it to evade immunity from poultry vaccines. This highlights the need for continued surveillance and monitoring of vaccine induced immunity, with experimental vaccine challenge studies being done where indicated.

In situhybridization for the detection of chicken anaemia virus in experimentally‐induced infection and field outbreaks

A double stranded DNA probe, biotinylated by random priming, was used for in situ hybridization of chicken anaemia virus (CAV) in thymus tissue. Hybridization was visualized with an alkaline phosphatase conjugated streptavidin biotin complex and the substrate New Fuchsin. The test was performed on both uninfected and CAV-, adenovirus- or infectious bursal disease virus-infected specified pathogen free White Leghorn chickens. In addition, both healthy commercial broilers and broilers with blue wing disease or with colisepticemia, were tested. Genomic CAV was detected in all CAV-infected and blue wing-diseased chickens. With the exception of one chicken with colisepticemia, which showed a unexpectedly positive reaction, all control chickens tested negative in the test developed.

Age related resistance to avian Leukosis virus II. influence of age at inoculation on mortality and congenital transmission

Six age groups of specified pathogen free White Leghorn chickens housed in the same filtered air, positive pressure building, were inoculated at 1 day, 2, 4, 6, 8 and 10 weeks of age respectively, with a mixture of leukosis viruses of subgroups A and B. Birds which died during the experiment were examined for gross and microscopical lesions. The incidence of lymphoid leukosis (LL) in the various groups was inversely proportional to the age of first virus exposure, Le., mortality was 62.5% in the group inoculated at 1-day-old and decreased to zero in the group inoculated at 10 weeks of age. In the age group inoculated at 8 weeks, only one chicken succumbed to the disease. Congenital transmission of leukosis virus (LV) was detected only in chickens inoculated immediately after hatching or at 2 weeks of age. In the latter group, all leukosis virus positive embryos were derived from one hen only. A seventh age group, housed in a separate filtered air, positive pressure building, served as uninoculated controls. Challenge infection was performed on the same day with chickens of all groups at ages varying from 59 to 71 weeks. Testing of pooled embryo extracts collected between 1 and 15 weeks post challenge did not change the virus shedding pattern. Even the chickens of the control group which were challenged (for the first time) at 71 weeks of age remained negative for congenital transmission. The results of this experiment show that the chickens inoculated with LV at 4 weeks of age or older had a low incidence of LL (decreasing to zero when the chickens were inoculated at 10 weeks of age) but did not congenitally shed virus.