|Sa E Silva, Mariana|
|Isakova Sivak, Irina|
Submitted to: International Poultry Scientific Forum
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2011
Publication Date: 1/23/2012
Citation: Sa E Silva, M., Rudenko, L., Isakova Sivak, I., Nguyen, T., Shu, Y., Cornelius, C., Donis, R., Swayne, D.E. 2012. Are vaccine viruses developed for pandemic preparedness a risk for poultry [abstract]. International Poultry Scientific Forum. p.73. Interpretive Summary:
Technical Abstract: Highly pathogenic avian influenza (HPAI) viruses are important agricultural pathogens and some have been transmitted to humans, especially H5N1, causing severe disease and death. Various HPAI viruses have the potential to become pandemic, and therefore national and international public health organizations are developing vaccine seed viruses that match the antigenic characteristics of the circulating viruses. These viruses are derived by reverse genetics to: i) include A/Puerto Rico/8/34 (PR8) genes that maximize their growth in eggs; and ii) delete the hemagglutinin (HA) polybasic cleavage site to minimize their pathogenicity. We evaluated HPAI vaccine candidate viruses to assess their virulence and infectivity for 4-to-6 week old chickens, by intravenous (IV) inoculation of 10 specific-pathogen-free chickens to determine the intravenous pathogenicity index (IVPI) per OIE protocol, which records clinical signs/death for 10 days. Another group of 10 birds was inoculated intranasally (IN). At 2 or 3 days post challenge, oropharyngeal and cloacal swabs are collected from all IN-challenged, and two are euthanized and tissues were collected for histopathology, immunohistochemistry (IHC), and virus isolation. At 14 days post challenge, birds were euthanized and bleed for serology, with agar gel immune diffusion or enzyme-linked immunosorbent assay (ELISA) test used to evaluate anti-influenza antibodies. Six recombinant viruses (subtypes H5N1, H5N2) and one wild type (H5N1) were tested. None of the vaccine candidate viruses showed evidence of infection after IN challenge (no virus isolated in tissue samples at 3 dpi, shedding, no detectable antibodies, no clinical signs or lesions), neither the IV challenge group showed any evidence of clinical disease. The wild type H5N1 was the only one to replicate, induce 100% mortality, virus shedding, typical lesions and immunohistochemical (IHC) antigen detection in tissues after IN challenge. The reassortment of avian viruses with a PR8 backbone, associated with the deletion of the cleavage site reduces the virulence inhibiting the ability of the viruses to infect chickens, generating safe vaccines that represent minimal risk for the poultry industry.