Abstract
Newcastle disease virus (NDV) can cause severe disease in chickens. Although NDV vaccines exist, there are frequent reports of outbreaks in vaccinated chickens. During 2009–2010, despite intense vaccination, NDV caused major outbreaks among commercial poultry farms in Indonesia. These outbreaks raised concern regarding the protective immunity of current vaccines against circulating virulent strains in Indonesia. In this study, we investigated whether a recombinant attenuated Indonesian NDV strain could provide better protection against prevalent Indonesian viruses. A reverse genetics system for the highly virulent NDV strain Banjarmasin/010/10 (Ban/010) isolated in Indonesia in 2010 was constructed. The Ban/010 virus is classified in genotype VII of class II NDV, which is genetically distinct from the commercial vaccine strains B1 and LaSota, which belong to genotype II, and shares only 89 and 87% amino acid identity for the protective antigens F and HN, respectively. A mutant virus, named Ban/AF, was developed in which the virulent F protein cleavage site motif “RRQKR↓F” was modified to an avirulent motif “GRQGR↓L” by three amino acid substitutions (underlined). The Ban/AF vaccine virus did not produce syncytia or plaques in cell culture, even in the presence of added protease. Pathogenicity tests showed that Ban/AF was completely avirulent. Ban/AF replicated efficiently during 10 consecutive passages in chickens and remained genetically stable. Serological analysis showed that Ban/AF induced higher neutralization and hemagglutination inhibition antibody titers against the prevalent viruses than the commercial vaccines B1 or LaSota. Both Ban/AF and commercial vaccines provided protection against clinical disease and mortality after challenge with virulent NDV strain Ban/010 (genotype VII) or GB Texas (genotype II). However, Ban/AF significantly reduced challenge virus shedding from the vaccinated birds compared to B1 vaccine. These results suggest that Ban/AF can provide better protection than commercial vaccines and is a promising vaccine candidate against NDV strains circulating in Indonesia.
Highlights
Newcastle disease (ND) is a highly contagious avian disease with worldwide distribution that can cause severe economic losses in poultry industry [1]
Eight Newcastle disease virus (NDV) strains that were isolated during ND outbreaks in commercial chickens in Indonesia during 2009 and 2010 [16] were evaluated for pathogenicity by mean death time (MDT) and intracerebral pathogenicity index (ICPI) tests (Table 1)
Newcastle disease is an economically important disease of poultry, and naturally occurring avirulent NDV strains such as LaSota or B1 are widely used as live attenuated vaccines all over the world
Summary
Newcastle disease (ND) is a highly contagious avian disease with worldwide distribution that can cause severe economic losses in poultry industry [1]. The etiologic agent, Newcastle disease virus (NDV), is an enveloped, cytoplasmic virus that is a member of the genus Avulavirus in the family Paramyxoviridae. The genome of NDV is a nonsegmented, single-stranded, negative-sense RNA that contains six genes encoding a nucleoprotein (N), a phosphoprotein (P), a matrix protein (M), a fusion glycoprotein (F), a hemagglutinin-neuraminidase glycoprotein (HN), a large polymerase protein (L), and an additional protein V that is expressed by RNA editing during synthesis of the P mRNA [2]. The HN protein is responsible for attachment to the host cell and the F protein mediates fusion of the viral envelope with the cell membrane. The F protein is synthesized as an inactive precursor (F0) that is cleaved by host cell protease into two biologically active F1 and F2 subunits that remain linked by a disulfide bond. Cleavage of the F protein is a prerequisite for virus entry and cell-to-cell fusion
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