Title: Recombinant Newcastle disease vaccines: risk for recombination, reversion to virulence, and spread in non-target species Authors
Submitted to: Biotechnology Risk Assessment Symposium
Publication Type: Abstract Only
Publication Acceptance Date: January 15, 2014
Publication Date: N/A
Interpretive Summary: Virulent strains of Newcastle disease virus (NDV) remains one of the leading causes of disease and death in chickens in the developing world. Vaccination with live NDV vaccine is performed worldwide to prevent sickness and death from these viruses. In the last few years vaccines have been made with NDV strains created in the laboratory, called recombinant NDV (rNDV). Some of these rNDV vaccines also include genes from other viruses, such as avian influenza virus (AIV), which allows the vaccine to protect the bird from both Newcastle disease and avian influenza. The goal of these experiments is to evaluate the risk associated with using rNDV, especially when other virulent NDV or highly pathogenic avian influenza viruses are also present. First, we infected chicken embryos (still in the egg) with a rNDV that contained a gene from a highly pathogenic AIV and then we also infected that same egg with a AIV that was not virulent to see if the combination of the two viruses might result in the creation of a virulent AIV that causes disease and death. Initial studies have shown that virulent AIV strains were not created during this experiment. Next, we wanted to infect chicken embryos with a rNDV that had one of the viral genes changed so that it wouldn’t cause disease in the bird, but we wanted to test if the virus over time might increase back to its original high virulence. Lastly, we infected pigeons with rNDV to see if they would get sick or shed the rNDV in saliva and feces. They did not get sick, but they did shed the virus in saliva and feces and they were able to infect other pigeons in their cage.
Technical Abstract: Newcastle disease (ND), caused by Newcastle disease virus (NDV), is one of the most important diseases of poultry and causes significant economic losses to the poultry industry worldwide. Vaccination is the main form of control of ND and it has been practiced for more than 60 years with billions of doses being used every year in commercial poultry around the world. Several recombinant NDV strains have been recently engineered and are commercially available around the world for use as live attenuated vaccines. The present study is being conducted to determine the risk associated with using live recombinant NDV vaccines in the field, especially in countries where highly pathogenic avian influenza virus (AIV) or virulent NDV are present. We are using a previously established embryonating chicken egg (ECEs)/cell culture screening protocol to assess three specific situations. First, to evaluate if recombinant NDV (rNDV) vaccines containing the hemagglutinin gene of the highly pathogenic subtype H5 of AIV can recombine with low path H5, H6 and H9 AIV strains, to produce a AIV with the virulence of the original H5 subtype. Next, to evaluate if rNDV vaccines containing an attenuated fusion (F) protein cleavage site can revert back to a virulent virus phenotype. Lastly, to test the ability of rNDV vaccines to infect and spread in non-target species such as pigeons, sparrows and starlings. The co-infection of 14-day-old ECEs with rNDV-LaSota/AI-H5 and LPAI strains rA/whooper/Mongolia/H5, A/duck/Penn/97 (H6), or A/ruddy_turnstone/NJ/02 (H9) (300/AIV strain) resulted in the dead of at least 90% of the embryos within 72 hours post-inoculation (h pi), as expected due to the AIV infection. Additional screening of allantoic fluids from these eggs without the addition of trypsin will discern if viruses with increased virulence is present. Infection of 14-day-old ECEs with wild type NDV strains LaSota and Australia or with recombinant NDV strains LaSota (rLaSota), M (rM), or ZJ1 (rZJ1*Lento) (900 eggs/virus), resulted in the dead of 65, 11, 30, 2 and 8 embryos, respectively within 72 h pi. Experiments to assess the ability of recombinant NDV vaccines to infect and spread in pigeons have shown that rLaSota, rM and rLaSota/AIV-H5 are able to infect and spread in this species. All virus-inoculated pigeons shed the virus in oral and/or cloacal secretions and at least one out of four contact birds shed the virus for two or more days. These preliminary findings suggest that our system is suitable to assess the risk associated with recombinant NDV vaccines.