Recombinant newcastle disease vaccines: risk for recombination, reversion to virulence, and spread in non-target species

Authors: DIEL, DIEGO - Former ARS Employee; HAMAL, KRISHNA - University Of Georgia; Afonso, Claudio; Suarez, David; Miller, Patti

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/11/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Newcastle disease virus (NDV) infection of chickens causes a range of clinical disease ranging from asymptomatic infection to severe disease with high mortality. When an outbreak of the virulent form of the virus occurs in poultry, the country is obligated to report it to the World Organization for Animal Health (O.I.E.) and trading partners often will suspend imports of poultry or poultry products from that country. When comparing the number of countries reporting outbreaks of 71 important animal diseases from 2006 to 2009, Newcastle Disease (ND) was the 2nd most prevalent disease reported in 56 of the 167 member countries of the O.I.E. Vaccination for NDV is almost universally practiced in commercial chickens around the world. Because there is evidence that having a NDV vaccine strain similar to your challenge virus is beneficial, recombinant NDV (rNDV) are being developed for this purpose using reverse genetics technology. While the target species for a rNDV vaccine are poultry species, NDV infects at least 250 bird species, including non-target, wild bird species that frequently interact with poultry. Avian influenza virus (AIV) is also an RNA virus with a broad host range including wild bird and poultry species. The virus has a segmented genome, and can easily swap any of the 8 gene segments with other AIV when they both infect the same host. Because of the concern for live viruses changing to virulence, either through reassortment or mutation (and recombination), live attenuated AI vaccines are not used for poultry. The usages of viral-vectored vaccines expressing the HA protein for AIV is quickly increasing. The rNDV vectored vaccines used in China and Mexico containing the hemagglutinin (HA) gene of AIV are commercially available and are used in the field. Roughly 5.1 billion doses of live rNDV vaccines containing the attenuated sequence of H5 HA gene of HPAI virus have been applied in China, alone, since 2005-2010. During a three-month period in 2008, 32 million doses of a similarly made rNDV vectored vaccine, (rNDV-AI), were applied in Mexico. The first aim was to determine if a novel virulent AIV can be created through homologous or non-homologous recombination of a rNDV expressing the attenuated AIV HA gene and a wild type (WT) AIV. We infected 14-day old embryos with NDV-AI/HA and low path AIV (H6 or H9or attenuated H5) and assessed recombination via sequencing and pathogenicity studies. There were 3 groups of NDV and AIV combinations and 111 samples demonstrated cytopathic effects (CPE) without trypsin, a potential indicator of increased virulence, and were treated to remove NDV from the samples and then each sample was inoculated into three 9-10-day-old SPF eggs to rescue the AIV in the sample. The RNA from 74 allantoic fluid samples that were hemagglutination positive were tested for the detection of NDV to ensure that complete NDV neutralization occurred. These RNA samples will be PCR amplified for AIV HA using specific primers. Primers have already been designed and are currently being optimized. The second aim is to determine the relative potential of rNDV isolates with attenuated fusion cleavage sites to revert back to virulence in a host organism using in vivo and in vitro methods. 900 14-day-old SPF embryos were infected for each of these viruses: WT LaSota, WT Australia, rLaSota, or attenuated rZJ1, resulting in the death of 7.2%, 1.1%, 2.5%, and 0.6% embryos, respectively within 72 h pi. Sequencing revealed no change in the fusion cleavage site and MDT, ICPI and pathogenesis are being completed. The goal of third aim is to determine the impact of rNDV and NDV-vectored vaccines on non-target species that are known to be susceptible to NDV and AIV with respect to infection and transmission. This aim will assess the susceptibility to the viruses and the ability of the viruses to be tr