Abstract:
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Six Newcastle disease virus (NDV) strains, Dikheinat-1990 (DIK-90), Dongola,
Gedarif.Elsoufi.1 (GD.S.1), I2, Lasota and Clone 30 were propagated in chicken
embryonated eggs and identified by hemagglutination inhibition test (HI). RNA
was extracted from allantoic fluid harvests of the various strains. Two step reverse
transcription-polymerase chain reactions (RT-PCR) were carried out, which
amplified 805 base pair (bp) of the first part, including the cleavage site, of the
fusion protein gene (F gene) of NDV strains using a set of gene specific primers.
Following sequencing, alignment of the resulted gene sequences were carried out
using ClustalX program. The annotation and subsequent steps were implemented
using MEGA 4 program. 714 bp were translated to protein sequence and used to
analyze the cleavage site motives of the F protein, which is a known virulent
determinant of NDV strains, in order to differentiate between virulent and a
virulent NDV strains. Genetic analyses of NDVs have demonstrated a relationship
between the amino acid sequence at the F protein cleavage site and virulence
among various strains. Results indicated that the three test strains Dongola,
GD.S.1, DIK-90 and the reference vaccinal strain Clone 30 have a motive of
avirulent NDV 112G-R-Q-G-R-L117, while the I2 and Lasota possessed the motif
of a typical low virulent NDV 112R-K-Q-G-R-L117 represented by lentogenic
strains. The two velogenic strains DIK-90 and GD.S.1 have the cleavage site
motive of lentogenic strain, unexpectedly. This suggests that the cleavage site
motif of the F protein is not the only factor that determines the virulence of NDV
strains. Phylogenetically from this study, it could be shown that all the strains
cluster into genotype II |