Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 23, 2012
Publication Date: June 18, 2012
Citation: Kapczynski, D.R. 2012. Cross clade protective efficacy of a recombinant HVT-H5 vaccine against lethal H5N1 and H5N2 avian influenza challenge [abstract]. CEVA Poultry Biology Expert Group Meeting. CDROM. Technical Abstract: Protective immunity against highly pathogenic avian influenza (HPAI) largely depends on the development of an antibody response against a subtype-specific lineage of challenge virus. In the poultry industry, inactivated AI vaccines are typically produced with indigenous AI isolates to provide the best flock protection. In this study, we compared protection of chickens provided by a recombinant turkey herpesvirus (rHVT) vaccine expressing the HA gene from a clade 2.2 H5N1 strain (A/swan/Hungary/4999/2006) against homologous H5N1 and heterologous H5N1 and H5N2 HPAI challenge. Groups of birds were vaccinated at day of age subcutaneously and challenged four weeks later with a homologous virus, A/whooper swan/Mongolia/L245/2005. The results demonstrated all vaccinated birds were protected from clinical signs of disease and mortality following lethal H5N1 challenge. In addition, oral and cloacal swabs taken from challenged birds demonstrated that vaccinated birds had lower incidence and titers of viral shedding compared to sham-vaccinated birds. To examine protection against genetically distant HPAI, birds were challenged with either a H5N1 of Indonesian origin or a H5N2 HPAI Mexican isolate. In those studies, 80-95% of vaccinated birds survived challenge, with few birds shedding virus after the challenge. Interestingly, prechallenge antibody titers against the challenge isolate did not appear to be at protective levels. Taken together, these studies provide support for the use of rHVT vaccines expressing HA to protect poultry against multiple lineages of HPAI, and that factors besides antibodies, namely cell-mediated immunity, may provide additional protective capacity.