Abstract
BackgroundHighly pathogenic (HP) H5N1 avian influenza virus (AIV) was introduced to Egyptian poultry in 2006 and has since become enzootic. Vaccination has been utilized as a control tool combined with other control methods, but for a variety of reasons, the disease has not been eradicated. In 2007, an antigenically divergent hemagglutinin subclade, 2.2.1.1, emerged from the original clade 2.2.1 viruses.ObjectivesThe objective was to evaluate four diverse AIV isolates for use as vaccines in chickens, including two commercial vaccines and two additional contemporary isolates, against challenge with numerous clade 2.2.1 and clade 2.2.1.1 H5N1 HPAIV Egyptian isolates to assess the variation in protection among different vaccine and challenge virus combinations.MethodsVaccination-challenge studies with four vaccines and up to eight challenge strains with each vaccine for a total of 25 vaccination-challenge groups were conducted with chickens. An additional eight groups served as sham-vaccinated controls. Mortality, mean death time, morbidity, virus, and pre-challenge antibodies were evaluated as metrics of protection. Hemagglutination inhibition data were used to visualize the antigenic relatedness of the isolates.Results and conclusionsAlthough all but one vaccine-challenge virus combination significantly reduced shed and mortality as compared to sham vaccinates, there were differences in protection among the vaccines relative to one another based on challenge virus. This emphasizes the difficulty in vaccinating against diverse, evolving virus populations, and the importance of selecting optimal vaccine seed strains for successful HPAIV control.
Highlights
Use of vaccination for the control of avian influenza virus (AIV) has become routine, combined with other control measures such as improved biosecurity in areas where H5N1 highly pathogenic (HP) AIV is endemic in poultry
Two of the most widely used have been A/goose/Guangdong/1/1996 which is the source of hemagglutinin (HA) and neuraminidase (NA) genes in the inactivated Re-1 vaccine[1] and A/Mexico/232/1994 H5N2 (Mex/94) low pathogenic (LP) AIV which is used in several inactivated commercial products
The Re-1 vaccine and the in-house vaccine produced with the Mex/94 isolate produced significantly higher levels of antibody than either of the experimental vaccines produced with the Egyptian H5N1 isolates: Egy/202/07 or Egy/13/08
Summary
Use of vaccination for the control of avian influenza virus (AIV) has become routine, combined with other control measures such as improved biosecurity in areas where H5N1 highly pathogenic (HP) AIV is endemic in poultry. Two of the most widely used have been A/goose/Guangdong/1/1996 which is the source of hemagglutinin (HA) and neuraminidase (NA) genes in the inactivated Re-1 vaccine[1] (use discontinued in China in mid-20082 its use continued in Egypt and Vietnam) and A/Mexico/232/1994 H5N2 (Mex/94) low pathogenic (LP) AIV which is used in several inactivated commercial products. Because of the ability of influenza A viruses to mutate and drift antigenically, there are reports of H5 field viruses which escaped immunity induced by these common vaccines a 2014 The Authors. Pathogenic (HP) H5N1 avian influenza virus (AIV) was introduced to Egyptian poultry in 2006 and has since become enzootic. In 2007, an antigenically divergent hemagglutinin subclade, 2.2.1.1, emerged from the original clade 2.2.1 viruses
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