Recombinant Newcastle Disease Vaccines: Risk for Recombination, Reversion to Virulence and Spread in Non-Target Species

NON-TECHNICAL SUMMARY: Billions of poultry vaccines made with live genetically modified viruses are currently being used in China and Mexico. Concerns over their ability to recombine or swap genes with viruses in the environment, increasing their ability to cause disease, exist. We propose to study this topic in a controlled experimental environment. We hypothesize that by co-infecting hosts with the modified vaccine virus along with a wild type virus, we will show whether these vaccines are stable and safe or that recombination is possible. The objectives are to evaluate if 1) a host infected with a Newcastle disease virus (NDV) containing one avian influenza (AI) gene and a wild type AI virus can recombine 2) a modified NDV can revert from a vaccine virus to a virulent virus and 3) these modified vaccine viruses can infect and transmit in wild bird species they were not intended for. We expect 1) to be able to produce recombination between a modified NDV containing an AI gene and a wild type AI virus, but do not expect that the occurrence of recombination will be common 2) that modified NDV without the AI gene will not revert to being a virulent NDV and 3) the non-target species will be infected with and be able transmit these vaccines. These studies, which will optimize the possibility of producing dangerous viruses from genetically modified viruses and wild viruses, may determine regulatory rules concerning the licensing of these vaccines in the U.S.A and potentially other areas of the world.<P>

APPROACH: We will use commercially available live vaccines from China or Mexico formulated with Newcastle disease viruses (NDV) containing the H5 hemagglutinin (HA) protein for avian influenza and/or NDV recombinants with H5 inserts made in our laboratory. We will utilize an NDV that has been modified by reverse genetics to include an attenuated hemagglutinin-neuraminidase (HN) or fusion (F) and HN genes from a virulent NDV. An established cell culture protocol that uses products from egg based studies will be performed to determine if 1) the avian influenza HA gene inserted in the NDV genome can recombine, by homologous or non-homologous recombination, with low pathogenic H5 and non H5 influenza viruses and 2) if the recombinant NDV (rNDV) containing an attenuated HN and/or F and HN genes from a virulent strain can revert back to a virulent virus. A wild type NDV, documented to have increased in virulence in nature in 1998, will be tested along side the rNDV. The protocol uses 14-day-old specific pathogen free (SPF) embryonated chicken eggs (ECE) and favors the growth of virulent viruses in cell culture, avoiding having to make multiple passages of egg fluids. Any viruses that form plaques in cell culture without the addition of an extraneous protease potentially have an increase in virulence and will have the HN and F genes sequenced to compare with parent virus. Selected viruses will be evaluated in embryos and birds to define the change in virulence. To assess non-target species infection for specific aim three, the three most common wild avian species associated with poultry houses; pigeons, starlings, and house sparrows, will be tested experimentally with rNDV and rNDV-H5 used in the first two specific aims to determine susceptibility to infection and for the potential of the virus to transmit and change within these species. Selected viruses recovered after infection will be viewed in the same egg based study to evaluate virulence.