Nucleotide and Amino acid changes map to Functional Domains on the Haemagglutinin of A/equine/Ibadan/4/91 (H3N8) influenza virus

The application of the method of rapid sequencing of equine influenza A virus A/equine/Ibadan/4/91 (H3N8) haemagglutinin (HA) gene in ELISA plates is reported. There was no nucleotide change compared with the sequence we earlier obtained for this virus by cycle sequencing which indicates that the present method is equally sensitive and specific but there was only one nucleotide change at position 478 compared to A/eq/Ibadan/6/91 (H3N8) isolated at the same time. Compared with prototype European strain, A/eq/Suffolk/89 (H3N8), nucleotide and amino acid changes observed in the HA of A/eq/Ibadan/4/91 mapped to functional domains of the molecule: signal peptide and antigenic sites. Nucleotide changes occurred at positions 45 (A→G), 478 (G→C), 562 (T→G), 805 (C→T) in HA1 and 1188 (G→A) in HA2 while amino acid changes occurred at residues 6 (I→V) in the signal peptide, 135 (R→T), 178 (I→T), 244 (T→M) in the HA1 and 43 (A→T) in the HA2. The change at residue 135 introduced a new potential asparagine-linked glycosylation site at residue 133. The genetic and antigenic implications of these changes are highlighted. The specificity and advantages of the method used over reverse transcription-polymerase chain reaction (RT-PCR) and cycle sequencing of PCR products are discussed.