Deduced Amino Acid Sequences Surrounding the Fusion Glycoprotein Cleavage Site and of the Carboxyl-terminus of Haemagglutinin–Neuraminidase Protein of the Avirulent Thermostable Vaccine Strain I-2 of Newcastle disease virus

Abstract

A single-tube RT-PCR technique generated a 387 bp or 300 bp cDNA amplicon covering the F(0) cleavage site or the carboxyl (C)-terminus of the HN gene, respectively, of Newcastle disease virus (NDV) strain I-2. Sequence analysis was used to deduce the amino acid sequences of the cleavage site of F protein and the C-terminus of HN protein, which were then compared with sequences for other NDV strains. The cleavage site of NDV strain I-2 had a sequence motif of (112) RKQGRLIG(119), consistent with an avirulent phenotype. Nucleotide sequencing and deduction of amino acids at the C-terminus of HN revealed that strain I-2 had a 7-amino-acid extension (VEILKDGVREARSSR. This differs from the virulent viruses that caused outbreaks of Newcastle disease in Australia in the 1930s and 1990s, which have HN extensions of 0 and 9 amino acids, respectively. Amino acid sequence analyses of the F and HN genes of strain I-2 confirmed its avirulent nature and its Australian origin.

Newcastle disease vaccine virus I-2 fails to acquire virulence during repeated passage in vivo

“…An example of such a vaccine is the naturally attenuated, thermotolerant I 2 ND virus, now commonly known as I-2, which has long been known to be a suitable vaccine for use in developing countries. This is due partly to its high titre yield in embryonated eggs, its lack of virulence, a low pathogenicity coupled to a high immunogenicity which confers substantial protection, its thermotolerance (at least 12 weeks when stored at 22 o C in 1% gelatin), its straightforward delivery routes including by eye drop, its contact spread between birds and its safety and efficacy in very young (8 day) African local ecotype chicks ( ACIAR, 2005 ; Bensink & Spradbrow, 1999 ; Copland & Alders, 2004 ; Dias et al, 2001 ; Domingue et al, 2017 ; Henning et al, 2009 ; Kattenbelt et al, 2006 ; Tu et al, 1998 ; Wambura et al, 2000 ; Wambura et al, 2006 ; Wambura et al, 2007 ). While the ND I-2 vaccine is thermotolerant, it eventually loses its potency if exposed to excessive sunlight or temperatures for long periods, i.e.…”