Pathotypic and genotypic characterization of two Bangladeshi isolates of Newcastle disease virus of chicken and pigeon origin.

Two Bangladeshi isolates of Newcastle disease virus (NDV), one from a chicken and one from a pigeon, were characterized in this study. Pathogenicity of the isolates was evaluated on the basis of intracerebral pathogenicity index (ICPI). Both the isolates were found to be of velogenic pathotype having ICPI of 1.83 and 1.51 for the chicken and pigeon isolate, respectively. Genotype of the isolates was determined by phylogenetic analysis based on partial F gene sequences. A 766-bp genome fragment spanning partial M and F gene was amplified by RT-PCR and sequenced. The first 354 bp of the coding region of F gene and corresponding deduced amino acid sequences (residues 1-118) of these two NDV isolates were aligned with that of other NDV strains retrieved from GenBank. A phylogenetic tree constructed from the alignment showed that the chicken isolate (BD-C162) belonged to the newly described genotype XIII and the pigeon isolate (BD-P01) to genotype VI. Both the chicken and pigeon isolates possessed a virulent-like fusion protein cleavage site (112) RRQKRF(117) .

Further evidence for the association of distinct amino acid residues with in vitro and in vivo growth of infectious bursal disease virus.

A cell-culture-adapted reverse genetics strain of very virulent infectious bursal disease virus (IBDV) of chickens, designated as BD-3tcC, having four amino acid substitutions (Gln253His, Asp279Asn, Ala284Thr and Ser330Arg) in the capsid protein VP2 was tested for its genetic stability during serial passage in chickens and chicken embryo fibroblast (CEF) cell culture. Results of in vitro and in vivo experiments demonstrated that all four introduced mutations in BD-3tcC remained stable during serial passage in CEF cell culture, but during passage in chickens, amino acid residues at position 253 and 284 reverted from histidine to glutamine and threonine to alanine, respectively. In a parallel experiment, the same substitutions also occurred in a conventionally attenuated vaccine strain D-78 on serial passage in chickens. However, no reversion or substitution took place at positions 279 and 330 during in vivo passage of the mutant virus BD-3tcC or vaccine virus D-78. The findings provide conclusive evidence that while IBDV requires histidine and threonine at positions 253 and 284 for cell culture adaptation, glutamine and alanine at these positions are selected preferentially during in vivo replication.

New introduction of clade 2.3.2.1 avian influenza virus (H5N1) into Bangladesh.

Since the first outbreak of highly pathogenic H5N1 avian inafluenza (HPAI) in Bangladesh in February 2007, a total of 519 disease events have been reported till 22 October 2011. Partial HA gene sequences of 11 selected H5N1 HPAI isolates of 2007 to 2011 were determined and subjected to phylogenetic analysis. The study revealed a recent introduction of clade 2.3.2 and 2.3.4 viruses into Bangladesh in 2011 in addition to clade 2.2 viruses that had been in circulation since 2007. Clade 2.3.2 virus isolates from Bangladesh are phylogenetically related to the newly designated clade 2.3.2.1 viruses, reported recently from Asia and Eastern Europe.