Variation in the spike protein of the 793/B type of infectious bronchitis virus, in the field and during alternate passage in chickens and embryonated eggs.

The degree of variation exhibited within the 793/B serotype (also known as 4/91 and CR88 serotypes) was investigated with nine French and 10 British isolates, collected between 1985 and 1994. The S1 part (1644 nucleotides) of the spike protein gene of the first known isolate of this serotype, FR/CR85131/85, had 95.9% to 97% nucleotide identity with the other isolates. Partial sequencing of isolates from Iran and Saudi Arabia, isolated in 2000, revealed approximately 95% nucleotide identity with European isolates, including the two live 793/B vaccinal strains, showing that they were not re-isolations of vaccinal virus. The data indicates that strains within the 793/B serotype have > or =96% nucleotide identity within the whole S1 gene and > or =93% nucleotide identity within the first 560 nucleotides, and > or =92% and > or =86% amino acid identities in the corresponding protein regions. This is similar to the identities exhibited within the Massachusetts serotype. Sequence analysis of a 793/B field isolate after passage in embryonated eggs, then in chickens and then again in eggs revealed selection for a serine and alanine at S1 amino acid position 95 in chicken-passaged and egg-passaged virus, respectively. There was no change in pathogenicity. This is the first demonstration at gene sequence level of host-driven selection for infectious bronchitis virus.

Subtype B avian metapneumovirus resembles subtype A more closely than subtype C or human metapneumovirus with respect to the phosphoprotein, and second matrix and small hydrophobic proteins.

Avian metapneumovirus (aMPV) subtype B (aMPV/B) nucleotide sequences were obtained for the phosphoprotein (P), second matrix protein (M2), and small hydrophobic protein (SH) genes. By comparison with sequences from other metapneumoviruses, aMPV/B was most similar to subtype A aMPV (aMPV/A) relative to the US subtype C isolates (aMPV/C) and human metapneumovirus (hMPV). Strictly conserved residues common to all members of the Pneumovirinae were identified in the predicted amino acid sequences of the P and M2 protein-predicted amino acid sequences. The Cys(3)-His(1) motif, thought to be important for binding zinc, was also present in the aMPV M2 predicted protein sequences. For both the P and M2-1 protein-predicted amino acid sequences, aMPV/B was most similar to aMPV/A (72 and 89% identity, respectively), having only approximately 52 and 70% identity, respectively, relative to aMPV/C and hMPV. Differences were more marked in the M2-2 proteins, subtype B having 64% identity with subtype A but < or = 25% identity with subtype C and hMPV. The A and B subtypes of aMPV had predicted amino acid sequence identities for the SH protein of 47%, and less than 20% with that of hMPV. An SH gene was not detected in the aMPV/C. Phylogenetically, aMPV/B clustered with aMPV/A, while aMPV/C grouped with hMPV.

Co-circulation of four types of infectious bronchitis virus (793/B, 624/I, B1648 and Massachusetts).

Eighteen isolates of infectious bronchitis virus (IBV) from Italy and Poland in 1997 to 1998 were comprehensively analysed by serum haemagglutination inhibition and virus neutralization tests, and by type-specific polymerase chain reactions and spike protein S1 gene sequencing. Four types of IBV (793/B, 624/I, B1648 and Massachusetts) were detected in Italy, while the presence of 793/B was confirmed in Poland. This showed that not only were four types of IBV co-existing within a single year, but also that several types of IBV have persisted in Europe for many years (at least 13 to 14 years for types B1648 and 793/B). Sequencing of the S1 gene of the 624/I isolate confirmed this as a unique type of IBV.