Evaluation of Newcastle disease virus with derivated Hemaggluti-nin-Neuraminidase gene of mesogenic strain

Abstract:

[Objective] The hemagglutinin-neuraminidase (HN) and fusion protein of Newcastle disease virus (NDV) plays a crucial role in the process of budding and infection. To understand the exact contribution of the HN gene to NDV pathogenecity, a reverse genetics system was developed using the lentogenic NDV LaSota strain . [Methods] the HN genes of an avirulent recombinant NDV strain (rLaSota) was replaced by an HN gene from Mukteswar mesogenic NDV strain by reverse genetics. Furthermore, the F gene of rL-MuHN was replaced with that of Mukteswar strain, resulting the double genes replaced chmeric virus, rL-MuFHN. [Results] Although the rescued chimeric virus (rL-MuHN) did not show significant increase in ability of hemadsorption, the intracerebral pathogenicity index test (ICPI=0) in chickens and mean death time for eggs (MDT≥90 h). rL-MuHN kept the low pathogenicity similar to its parent rLaSota strain. Compared to single gene replaced rL-MuHN, rL-MuFHN induced stronger cell fusion and showed a mild increase in ICPI (from 0 to 0.59) and no significant change in MDT (≥90 h). rL-MuFHN showed much lower pathogenicity than that of Mukteswar (ICPI.=1.32 and MDT=46,respectively). A HN gene exchange alone within the context of the NDV rLaSota backbone failed to increase virus virulence from unvelogenic to mesogenic pathotype. [Conclusion] These results indicated that the virulence of NDV is determined multigenically. The heterotypic HN and F pairs were not equally effective in virus pathogenicity. The HN gene derivated from mesogenic strain dose not alter the lentogenic property of NDV LaSota strain. NDV can be manipulated by gene replacement in the future for use as a vaccine candidate.