Senne D A, Suarez D L, Pedersen J C, Panigrahy B
National Veterinary Services Laboratories, P. O. Box 844, Ames, IA 50010, USA.
Avian Dis. 2003;47(3 Suppl):898-904. doi: 10.1637/0005-2086-47.s3.898.
Surveillance for H5 and H7 subtypes of avian influenza virus (AIV) in the live-bird markets (LBMs) of the northeastern United States has been in effect since 1986 when the markets were first recognized as a potential reservoir for AIV. Long-term maintenance of AIV in the LBM system has been documented. However, little is known about the influence of successive cycles of replication in unnatural avian hosts (gallinaceous birds) on the genetics of the virus, especially in the region of the hemagglutinin (HA) gene that can influence pathogenicity. Isolation of low-pathogenicity H5 AIVs from the LBMs has been sporadic; however, in 1994 a low-pathogenicity H7N2 virus was isolated that has persisted in the LBMs for more than 7 yr. Efforts to eliminate the H7 virus from the markets have been unsuccessful. During the 7-yr period, several molecular changes have occurred at the hemagglutinin cleavage site of the H7 virus. These changes include substitutions of proline for threonine and lysine for asparagine, respectively, at the -2 and -5 positions of the HA1 protein. In addition, there has been a 24 nucleotide base-pair deletion in the receptor binding region of the HA1. The accumulation of an additional basic amino acid at the cleavage site is a cause for concern to regulatory authorities, and, therefore, efforts to eliminate the virus from the LBM system have been intensified.
自1986年起，美国东北部活禽市场（LBMs）就开始对H5和H7亚型禽流感病毒（AIV）进行监测，当时这些市场首次被认定为AIV的潜在储存宿主。已有文献记载AIV在LBM系统中的长期存在情况。然而，对于该病毒在非天然禽类宿主（鸡形目鸟类）中连续复制周期对其遗传学的影响，尤其是对可能影响致病性的血凝素（HA）基因区域的影响，人们了解甚少。从LBMs中零星分离出低致病性H5 AIV；然而，1994年分离出一种低致病性H7N2病毒，该病毒已在LBMs中持续存在超过7年。从市场上消除H7病毒的努力一直未成功。在这7年期间，H7病毒的血凝素裂解位点发生了一些分子变化。这些变化包括在HA1蛋白的-2和-5位置分别将苏氨酸替换为脯氨酸以及将天冬酰胺替换为赖氨酸。此外，HA1的受体结合区域有24个核苷酸碱基对缺失。裂解位点额外碱性氨基酸的积累引起了监管当局的关注，因此，从LBM系统中消除该病毒的努力已经加强。
