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Acquisition of human-type receptor binding specificity by new H5N1 influenza virus sublineages during their emergence in birds in Egypt.

Watanabe Y, Ibrahim MS, Ellakany HF, Kawashita N, Mizuike R, Hiramatsu H, Sriwilaijaroen N, Takagi T, Suzuki Y, Ikuta K - PLoS Pathog. (2011)

Bottom Line: The phylogenetic results showed that recent human isolates clustered disproportionally into several new H5 sublineages suggesting that their HAs have changed their receptor specificity.Using reverse genetics, we found that these H5 sublineages have acquired an enhanced binding affinity for α2,6 SA in combination with residual affinity for α2,3 SA, and identified the amino acid mutations that produced this new receptor specificity.Interestingly, these H5 viruses, with increased affinity to α2,6 SA, emerged during viral diversification in bird populations and subsequently spread to humans.

View Article: PubMed Central - PubMed

Affiliation: Department of Virology, Research Institute for Microbial Diseases (BIKEN), Osaka University, Osaka, Japan. nabe@biken.osaka-u.ac.jp

ABSTRACT
Highly pathogenic avian influenza A virus subtype H5N1 is currently widespread in Asia, Europe, and Africa, with 60% mortality in humans. In particular, since 2009 Egypt has unexpectedly had the highest number of human cases of H5N1 virus infection, with more than 50% of the cases worldwide, but the basis for this high incidence has not been elucidated. A change in receptor binding affinity of the viral hemagglutinin (HA) from α2,3- to α2,6-linked sialic acid (SA) is thought to be necessary for H5N1 virus to become pandemic. In this study, we conducted a phylogenetic analysis of H5N1 viruses isolated between 2006 and 2009 in Egypt. The phylogenetic results showed that recent human isolates clustered disproportionally into several new H5 sublineages suggesting that their HAs have changed their receptor specificity. Using reverse genetics, we found that these H5 sublineages have acquired an enhanced binding affinity for α2,6 SA in combination with residual affinity for α2,3 SA, and identified the amino acid mutations that produced this new receptor specificity. Recombinant H5N1 viruses with a single mutation at HA residue 192 or a double mutation at HA residues 129 and 151 had increased attachment to and infectivity in the human lower respiratory tract but not in the larynx. These findings correlated with enhanced virulence of the mutant viruses in mice. Interestingly, these H5 viruses, with increased affinity to α2,6 SA, emerged during viral diversification in bird populations and subsequently spread to humans. Our findings suggested that emergence of new H5 sublineages with α2,6 SA specificity caused a subsequent increase in human H5N1 influenza virus infections in Egypt, and provided data for understanding the virus's pandemic potential.

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Mortality and weight loss of mice infected with rEG/D1 viruses.Six-week-old BALB/c mice (7–8 mice per group) were inoculated intranasally with the indicated doses of rEG/D1, rEG/D1Q192H, rEG/D1129Δ,I151T, rEG/D1-EG/12 HA and rEG/D1-EG/12 HAH192Q. (A) Body weight of infected mice was monitored up to 14 d post-infection. Mean percent body weight change (±SD) for each group of mice is shown. (B) Survival of mice inoculated with rEG/D1 viruses. Mortality was calculated including mice that were sacrificed because they had lost more than 30% of their body weight. (C) Virus titers in lungs of mice infected with 3×104 or 3×105 FFU rEG/D1 at the indicated times post-infection. Circles and diamonds indicate values in individual mice.
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ppat-1002068-g008: Mortality and weight loss of mice infected with rEG/D1 viruses.Six-week-old BALB/c mice (7–8 mice per group) were inoculated intranasally with the indicated doses of rEG/D1, rEG/D1Q192H, rEG/D1129Δ,I151T, rEG/D1-EG/12 HA and rEG/D1-EG/12 HAH192Q. (A) Body weight of infected mice was monitored up to 14 d post-infection. Mean percent body weight change (±SD) for each group of mice is shown. (B) Survival of mice inoculated with rEG/D1 viruses. Mortality was calculated including mice that were sacrificed because they had lost more than 30% of their body weight. (C) Virus titers in lungs of mice infected with 3×104 or 3×105 FFU rEG/D1 at the indicated times post-infection. Circles and diamonds indicate values in individual mice.

Mentions: To assess the effect of enhanced α2,6 SA binding on pathogenicity of H5N1 isolates from Egypt, BALB/c mice were inoculated intranasally with different dilutions of selected recombinant viruses. Mice inoculated with 3×104 FFU rEG/D1Q192H, rEG/D1129Δ,I151T or rEG/D1-EG/12 HA showed considerable weight loss (Figure 8A). In contrast, mice inoculated with 3×104 FFU rEG/D1 or rEG/D1-EG/12 HAH192Q showed no clinical effects during the 14 d observation period, and most mice infected with 3×105 FFU of these viruses survived. The lethality of rEG/D1Q192H, rEG/D1129Δ,I151T and rEG/D1-EG/12 HA was substantially higher: the MLD50 was 8.8×102 FFU for rEG/D1Q192H, 1.5×103 FFU for rEG/D1129Δ,I151T and 1.3×104 FFU for rEG/D1-EG/12 HA (Figure 8B), >50 times less than the MLD50 of 5.9×105 FFU for both rEG/D1 and rEG/D1-EG/12 HAH192Q. Consistent with this result, the virus yield in lungs of mice infected with 3×104 FFU of the three viruses was >10-fold higher 4 d post-infection and >110-fold higher 7 d post-infection, and at a dose of 3×105 FFU was >70-fold higher 4 d post-infection than with parental rEG/D1 virus (Figure 8C).


Acquisition of human-type receptor binding specificity by new H5N1 influenza virus sublineages during their emergence in birds in Egypt.

Watanabe Y, Ibrahim MS, Ellakany HF, Kawashita N, Mizuike R, Hiramatsu H, Sriwilaijaroen N, Takagi T, Suzuki Y, Ikuta K - PLoS Pathog. (2011)

Mortality and weight loss of mice infected with rEG/D1 viruses.Six-week-old BALB/c mice (7–8 mice per group) were inoculated intranasally with the indicated doses of rEG/D1, rEG/D1Q192H, rEG/D1129Δ,I151T, rEG/D1-EG/12 HA and rEG/D1-EG/12 HAH192Q. (A) Body weight of infected mice was monitored up to 14 d post-infection. Mean percent body weight change (±SD) for each group of mice is shown. (B) Survival of mice inoculated with rEG/D1 viruses. Mortality was calculated including mice that were sacrificed because they had lost more than 30% of their body weight. (C) Virus titers in lungs of mice infected with 3×104 or 3×105 FFU rEG/D1 at the indicated times post-infection. Circles and diamonds indicate values in individual mice.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3102706&req=5

ppat-1002068-g008: Mortality and weight loss of mice infected with rEG/D1 viruses.Six-week-old BALB/c mice (7–8 mice per group) were inoculated intranasally with the indicated doses of rEG/D1, rEG/D1Q192H, rEG/D1129Δ,I151T, rEG/D1-EG/12 HA and rEG/D1-EG/12 HAH192Q. (A) Body weight of infected mice was monitored up to 14 d post-infection. Mean percent body weight change (±SD) for each group of mice is shown. (B) Survival of mice inoculated with rEG/D1 viruses. Mortality was calculated including mice that were sacrificed because they had lost more than 30% of their body weight. (C) Virus titers in lungs of mice infected with 3×104 or 3×105 FFU rEG/D1 at the indicated times post-infection. Circles and diamonds indicate values in individual mice.
Mentions: To assess the effect of enhanced α2,6 SA binding on pathogenicity of H5N1 isolates from Egypt, BALB/c mice were inoculated intranasally with different dilutions of selected recombinant viruses. Mice inoculated with 3×104 FFU rEG/D1Q192H, rEG/D1129Δ,I151T or rEG/D1-EG/12 HA showed considerable weight loss (Figure 8A). In contrast, mice inoculated with 3×104 FFU rEG/D1 or rEG/D1-EG/12 HAH192Q showed no clinical effects during the 14 d observation period, and most mice infected with 3×105 FFU of these viruses survived. The lethality of rEG/D1Q192H, rEG/D1129Δ,I151T and rEG/D1-EG/12 HA was substantially higher: the MLD50 was 8.8×102 FFU for rEG/D1Q192H, 1.5×103 FFU for rEG/D1129Δ,I151T and 1.3×104 FFU for rEG/D1-EG/12 HA (Figure 8B), >50 times less than the MLD50 of 5.9×105 FFU for both rEG/D1 and rEG/D1-EG/12 HAH192Q. Consistent with this result, the virus yield in lungs of mice infected with 3×104 FFU of the three viruses was >10-fold higher 4 d post-infection and >110-fold higher 7 d post-infection, and at a dose of 3×105 FFU was >70-fold higher 4 d post-infection than with parental rEG/D1 virus (Figure 8C).

Bottom Line: The phylogenetic results showed that recent human isolates clustered disproportionally into several new H5 sublineages suggesting that their HAs have changed their receptor specificity.Using reverse genetics, we found that these H5 sublineages have acquired an enhanced binding affinity for α2,6 SA in combination with residual affinity for α2,3 SA, and identified the amino acid mutations that produced this new receptor specificity.Interestingly, these H5 viruses, with increased affinity to α2,6 SA, emerged during viral diversification in bird populations and subsequently spread to humans.

View Article: PubMed Central - PubMed

Affiliation: Department of Virology, Research Institute for Microbial Diseases (BIKEN), Osaka University, Osaka, Japan. nabe@biken.osaka-u.ac.jp

ABSTRACT
Highly pathogenic avian influenza A virus subtype H5N1 is currently widespread in Asia, Europe, and Africa, with 60% mortality in humans. In particular, since 2009 Egypt has unexpectedly had the highest number of human cases of H5N1 virus infection, with more than 50% of the cases worldwide, but the basis for this high incidence has not been elucidated. A change in receptor binding affinity of the viral hemagglutinin (HA) from α2,3- to α2,6-linked sialic acid (SA) is thought to be necessary for H5N1 virus to become pandemic. In this study, we conducted a phylogenetic analysis of H5N1 viruses isolated between 2006 and 2009 in Egypt. The phylogenetic results showed that recent human isolates clustered disproportionally into several new H5 sublineages suggesting that their HAs have changed their receptor specificity. Using reverse genetics, we found that these H5 sublineages have acquired an enhanced binding affinity for α2,6 SA in combination with residual affinity for α2,3 SA, and identified the amino acid mutations that produced this new receptor specificity. Recombinant H5N1 viruses with a single mutation at HA residue 192 or a double mutation at HA residues 129 and 151 had increased attachment to and infectivity in the human lower respiratory tract but not in the larynx. These findings correlated with enhanced virulence of the mutant viruses in mice. Interestingly, these H5 viruses, with increased affinity to α2,6 SA, emerged during viral diversification in bird populations and subsequently spread to humans. Our findings suggested that emergence of new H5 sublineages with α2,6 SA specificity caused a subsequent increase in human H5N1 influenza virus infections in Egypt, and provided data for understanding the virus's pandemic potential.

Show MeSH
Related in: MedlinePlus