SURVEY OF THE HEMAGGLUTININ (HA) CLEAVAGE SITE SEQUENCE OF H5 AND H7 AVIAN INFLUENZA-VIRUSES - AMINO-ACID-SEQUENCE AT THE HA CLEAVAGE SITE AS A MARKER OF PATHOGENICITY POTENTIAL

The deduced amino acid sequence at the hemagglutinin (HA) cleavage sit e of 76 avian influenza (AI) viruses, subtypes H5 and H7, was determin ed by reverse transcription-polymerase chain reaction and cycle sequen cing techniques to assess pathogenicity Eighteen of the 76 viruses wer e isolated in 1993 and 1994 from various sources in the United States. In addition, 34 H5 (4 highly pathogenic [HP] and 30 non-highly pathog enic [non-HP]) and 24 H7 (3 HP and 21 non-HP) repository viruses, isol ated between 1927 and 1992, were sequenced and the sequences compared to chose in recent isolates. All repository HP H5 and H7 viruses studi ed had multiple basic amino acids adjacent to the HA cleavage site and most had basic amino acids in excess of the proposed minimum motif B- X-B-R (B = basic amino acids arginine or lysine, X = nonbasic amino ac id, R = arginine) chat has been associated with high pathogenicity. Of the non-HP viruses studied, 35 of 38 for H5 and 30 of 31 for H7 confo rmed to the motif B-X-X-R and B-X-R, respectively. Two non-HP H5 virus es had the mot if X-X-X-R ar the cleavage sire and a third had the mot if B-X-X-K (K = basic amino acid lysine). One non-KP H7 (A/Pekin robin /CA/30412-5/94) had four basic amino acids (K-R-R-R) adjacent to the c leavage sire. Although the Pekin robin isolate did nor produce disease in chickens under the conditions of the study it did have che amino a cid sequence compatible with that in HP AI viruses and, therefore, is considered potentially HP This is the first account of an H7 virus tha t is non-HP in chickens but meets the molecular criterion to be classi fied as HP.