Positive selection at the receptor-binding site of haemagglutinin H5 in viral sequences derived from human tissues

Abstract

Highly pathogenic H5N1 avian influenza virus has spread through at least 45 countries in three continents. Despite the ability to infect and cause severe disease in humans, the virus cannot transmit efficiently from human to human. The lack of efficient transmission indicates the incompletion of the adaptation of the avian virus to the new host species. The required mutations for the complete adaptation and the emergence of a potential pandemic virus are likely to originate and be selected within infected human tissues. Differential receptor preference plays an important role in the species-tropism of avian influenza. We have analysed quasispecies of sequences covering the receptor-binding domain of the haemagglutinin gene of H5N1 viruses derived from fatal human cases. We employed a likelihood ratio test to identify positive-selection sites within the quasispecies. Nine of seventeen positive-selection sites identified in our analyses were found to be located within or flanking the receptor-binding domain. Some of these mutations are known to alter receptor-binding specificity. This suggests that our approach could be used to screen for mutations with significant functional impact. Our data provide new candidate mutations for the viral adaptation to a human host, and a new approach to search for new genetic markers of potential pandemic viruses.

Reassortment between avian H5N1 and human H3N2 influenza viruses creates hybrid viruses with substantial virulence

“…Therefore, we anticipate that the introduction of the human PB2 segment into a reassortant virus could confer efficient growth at the lower temperature of the upper respiratory tract of humans, an ability that is critical for efficient transmission of pandemic viruses among humans (20). To initiate pandemics, influenza viruses also need to acquire human-like receptor-binding specificity with α2,6-linked sialic acid (21)(22)(23), an ability that has been partially achieved by some H5N1 human isolates (7,24,25).…”

“…2B): All four mice died when infected with 10 4.0 pfu of one of these 22 viruses. Substantial body weight loss was observed for all mice infected with these viruses, and the mean survival times were <10 days for most of the viruses (with three exceptions: r1,2,3,6, r1,3,5,7, and r1, 3,7,8). Importantly, 10 viruses were lethal to mice with an MLD 50 ≤100 pfu.…”

“…Therefore, the MLD 50 was ≥ 10 4.5 pfu. Mice infected with most of the viruses in this group experienced an increase in body weight at the end of the observation period (with a few exceptions; see viruses r3, r7, r1,8, r2,3, r3,7, and r1, 3,6,7). Among the 75 viruses tested, 32 viruses in the highly replicative group and all 13 viruses in the moderately replicative group were less pathogenic than the SK06 virus.…”

“…Soon afterwards, it infected 18 people in Hong Kong, six of whom died as a result of the infection (5,6). Since the H5N1 influenza outbreak in Asian poultry in 2003 (8), H5N1 influenza viruses have spread to wild birds and poultry in several continents (7) and have resulted in 442 confirmed human cases and 262 deaths (World Health Organization; http://www.who.int). Fortunately, the H5N1 viruses still lack the ability to transmit efficiently among humans.…”

In Vitro Assessment of Attachment Pattern and Replication Efficiency of H5N1 Influenza A Viruses with Altered Receptor Specificity

“…60%, the effect of such a pandemic on the human population could be devastating. In recent years, several amino acid substitutions in HA of HPAI H5N1 viruses have been described, either in virus isolates from patients or introduced experimentally, that increased the binding of the HPAI H5N1 HA to ␣2,6-linked SA (1,2,10,14,16,29,39,40). However, none of the described substitutions conferred a full switch of receptor specificity from ␣2,3-linked SA to ␣2,6-linked SA and the substitutions were described in virus strains of different geographical origins.…”