Analysis of Vis-NIR spectra changes to measure the inflammatory response in the nasal mucosal region of influenza A and B virus-infected patients

BACKGROUND

Human influenza A and B viruses cause severe seasonal respiratory tract infections, especially in infants and young children. Influenza A and B viruses have been reported to produce different symptoms and/or severity in infected patients, although these remain inconclusive.

OBJECTIVES AND STUDY DESIGN

In this study, non-invasive visible and near-infrared (Vis-NIR) spectroscopy was used for comparative analysis of the inflammatory response to influenza A and B virus infections, by measuring changes in water peak (970 nm) spectra collected from patient nasal mucosal regions.

RESULTS

The results suggested that infection with influenza B virus induced more severe inflammatory responses in the nasal mucosal region than influenza A virus.

CONCLUSIONS

These are the first data showing different inflammatory responses to influenza A and B viruses at the sites of virus infection.

Discovery of novel low-molecular-weight HIV-1 inhibitors interacting with cyclophilin A using in silico screening and biological evaluations

Cyclophilin A has attracted attention recently as a new target of anti-human immunodeficiency virus type 1 (HIV-1) drugs. However, so far no drug against HIV-1 infection exhibiting this mechanism of action has been approved. To identify new potent candidates for inhibitors, we performed in silico screening of a commercial database of more than 1,300 drug-like compounds by using receptor-based docking studies. The candidates selected from docking studies were subsequently tested using biological assays to assess anti-HIV activities. As a result, two compounds were identified as the most active. Specifically, both exhibited anti-HIV activity against viral replication at a low concentration and relatively low cytotoxicity at the effective concentration inhibiting viral growth by 50 %. Further modification of these molecules may lead to the elucidation of potent inhibitors of HIV-1.

Figure

Discrimination of influenza virus-infected nasal fluids by Vis-NIR spectroscopy

BACKGROUND

Influenza patients show a severe condition of the respiratory tract with high temperature. Efficient treatment of influenza requires early use of oseltamivir, and thus rapid diagnosis is needed. Recently, rapid diagnostic methods such as immunochromatography have been developed; however, immunochromatography is not an optimal technique because it is relatively expensive and has low sensitivity.

METHODS

Visible and near-infrared (Vis-NIR) spectroscopy in the region 600-1100 nm, combined with chemometrics analysis such as principal component analysis (PCA) or soft modeling of class analogy (SIMCA), was used to develop a potential diagnostic method for influenza based on nasal aspirates from infected patients.

RESULTS

The Vis-NIR spectra of nasal aspirates from 33 non-influenza patients and 34 influenza patients were subjected to PCA and SIMCA to develop multivariate models to discriminate between influenza and non-influenza patients. These models were further assessed by the prediction of 126 masked measurements [30 from non-influenza patients, 30 from influenza patients and 66 from patients infected with respiratory syncytial virus (RSV)]. The PCA model showed some discrimination of the masked samples. The SIMCA model correctly predicted 29 of 30 (96.7%) non-influenza patients, and 30 of 30 (100%) influenza patients from the Vis-NIR spectra of masked nasal aspirate samples. Nasal aspirates of RSV-infected patients were predicted as 50% non-influenza and 50% influenza by the SIMCA model, suggesting that discrimination between patients infected with influenza virus and those infected with RSV was difficult.

CONCLUSIONS

Although the study sample was small and there was difficulty in discriminating between influenza virus and RSV infection, these results suggest that Vis-NIR spectroscopy of nasal aspirates, combined with chemometrics analysis, might be a potential tool for diagnosis of influenza.

Chikungunya virus induces a more moderate cytopathic effect in mosquito cells than in mammalian cells

OBJECTIVES

Chikungunya virus (CHIKV) is an alphavirus belonging to the Togaviridae family. Alphaviruses cause a chronic non-cytopathic infection in mosquito cells, while they develop a highly cytopathic infection in cells originating from various vertebrates. In this study, we compared the cytopathic effect (CPE) induced by CHIKV in Vero cells and a mosquito cell line, C6/36 cells.

METHODS

CPE and the virus titers were compared between the CHIKV-infected C6/36 and Vero cells. Apoptosis was measured by TUNEL assay, and the differences between the C6/36 and Vero cells were compared.

RESULTS

CHIKV infection induced strong CPE and apoptosis in the Vero cells, but light CPE in the C6/36 cells. The virus titers produced in the C6/36 cells were much higher than those produced in the Vero cells.

CONCLUSIONS

The reason CHIKV induced strong CPE is that this virus triggers strong apoptosis in Vero cells compared with C6/36 cells. CHIKV established a persistent infection in C6/36 cells after being passaged 20 times. CHIKV infection in mosquito cells was distinct from that in Vero cells. The cell and species specificity of CHIKV-induced cell death implies that the cellular and viral regulators involved in apoptosis may play an important role in determining the outcome of CHIKV infection.

Significant neutralizing activities against H2N2 influenza A viruses in human intravenous immunoglobulin lots manufactured from 1993 to 2010

Influenza A H2N2 virus, also known as the Asian flu, spread worldwide from 1957 to 1967, although there have been no cases reported in humans in the past 40 years. A vaccination program was introduced in Japan in the 1960s. Older Japanese donors could have been naturally infected with the H2N2 virus or vaccinated in the early 1960s. Human intravenous immunoglobulin (IVIG) reflects the epidemiological status of the donating population in a given time period. Here, the possible viral neutralizing (VN) activities of IVIG against the H2N2 virus were examined. Hemagglutination inhibition (HI) and VN activities of IVIG lots manufactured from 1993 to 2010 in Japan and the United States were evaluated against H2N2 viruses. High HI and VN activities against H2N2 viruses were found in all the IVIG lots investigated. HI titers were 32-64 against the isolate in 1957 and 64-128 against the isolates in 1965. VN titers were 80-320 against the isolate in 1957 and 1280-5120 against the isolates in 1965. Both the HI and VN titers were higher against the isolate in 1965 than in 1957. Thus, antibody titers of IVIG against influenza viruses are well correlated with the history of infection and the vaccine program in Japan. Therefore, evaluation of antibody titers provides valuable information about IVIGs, which could be used for immune stimulation when a new influenza virus emerges in the human population.

Antigenic analysis of highly pathogenic avian influenza virus H5N1 sublineages co-circulating in Egypt

Highly pathogenic avian influenza virus H5N1 has spread across Eurasia and Africa, and outbreaks are now endemic in several countries, including Indonesia, Vietnam and Egypt. Continuous circulation of H5N1 virus in Egypt, from a single infected source, has led to significant genetic diversification with phylogenetically separable sublineages, providing an opportunity to study the impact of genetic evolution on viral phenotypic variation. In this study, we analysed the phylogeny of H5 haemagglutinin (HA) genes in influenza viruses isolated in Egypt from 2006 to 2011 and investigated the effect of conserved amino acid mutations in the HA genes in each of the sublineages on their antigenicity. The analysis showed that viruses in at least four sublineages still persisted in poultry in Egypt as of 2011. Using reverse genetics to generate HA-reassortment viruses with specific HA mutations, we found antigenic drift in the HA in two influenza virus sublineages, compared with the other currently co-circulating influenza virus sublineages in Egypt. Moreover, the two sublineages with significant antigenic drift were antigenically distinguishable. Our findings suggested that phylogenetically divergent H5N1 viruses, which were not antigenically cross-reactive, were co-circulating in Egypt, indicating that there was a problem in using a single influenza virus strain as seed virus to produce influenza virus vaccine in Egypt and providing data for designing more efficacious control strategies in H5N1-endemic areas.

Jurkat cell proliferation is suppressed by Chlamydia (Chlamydophila) pneumoniae infection accompanied with attenuation of phosphorylation at Thr389 of host cellular p70S6K

Chlamydia (Chlamydophila) pneumoniae infects T lymphocytes and multiplies within them. Our previous studies have indicated that C. pneumoniae infection suppresses proliferation of peripheral blood mononuclear cells stimulated with Staphylococcus-enterotoxin B; however, the mechanism of suppression was unclear. In this study, we explored the molecular mechanism involved in C. pneumoniae infection by using human acute T cell leukemia cell line, Jurkat E6-1. Proliferation of Jurkat cells was suppressed in an m.o.i.-dependent manner by C. pneumoniae infection. The suppression by the infection was particularly evident during the initial 24h of the infection, and down modulation of cyclin D3 protein levels were observed at the same time period by immunoblot analysis. The suppression of the Jurkat cell proliferation and the down modulation of cyclin D3 protein level were only induced by viable C. pneumoniae infection, not by exposure to UV-killed or heat-killed C. pneumoniae. Phosphorylations at Thr308 and Ser473 of AKT were induced by C. pneumoniae infection; however, phosphorylation at Thr389 of the downstream kinase, p70S6K was inhibited by unidentified mechanism associated with C. pneumoniae infection. Taking into account that G1 arrest of the C. pneumoniae infected Jurkat cells were not observed and that p70S6K is one of the most important regulators of protein synthesis, it was suggested that the suppression of Jurkat cell proliferation by C. pneumoniae was at least in part mediated by down modulation of protein synthesis through attenuation of Thr389 phosphorylation of p70S6K.

Human monoclonal antibodies to neutralize all dengue virus serotypes using lymphocytes from patients at acute phase of the secondary infection

The global spread of the four dengue virus serotypes (DENV-1 to -4) has made this virus a major and growing public health concern. Generally, pre-existing neutralizing antibodies derived from primary infection play a significant role in protecting against subsequent infection with the same serotype. By contrast, these pre-existing antibodies are believed to mediate a non-protective response to subsequent heterotypic DENV infections, leading to the onset of dengue illness. In this study, we prepared hybridomas producing human monoclonal antibodies (HuMAbs) against DENV using peripheral blood mononuclear cells (PBMCs) from patients in the acute phase (around 1 week after the onset of illness) or the convalescent phase (around 2weeks after the onset of illness) of secondary infection. Interestingly, a larger number of hybridoma clones was obtained from patients in the acute phase than from those in the convalescent phase. Most HuMAbs from acute-phase infections were cross-reactive with all four DENV serotypes and showed significant neutralization activity to all four DENV serotypes. Thus, secondary DENV infection plays a significant role in stimulating memory cells to transiently increase the number of antibody-secreting plasma cells in patients in the early phase after the secondary infection. These HuMAbs will enable us to better understand the protective and pathogenic effects of DENV infection, which could vary greatly among secondarily-infected individuals.

Poly (I:C), an agonist of toll-like receptor-3, inhibits replication of the Chikungunya virus in BEAS-2B cells

Background

Double-stranded RNA (dsRNA) and its mimic, polyinosinic acid: polycytidylic acid [Poly (I:C)], are recognized by toll-like receptor 3 (TLR3) and induce interferon (IFN)-β in many cell types. Poly (I:C) is the most potent IFN inducer. In in vivo mouse studies, intraperitoneal injection of Poly (I:C) elicited IFN-α/β production and natural killer (NK) cells activation. The TLR3 pathway is suggested to contribute to innate immune responses against many viruses, including influenza virus, respiratory syncytial virus, herpes simplex virus 2, and murine cytomegalovirus. In Chikungunya virus (CHIKV) infection, the viruses are cleared within 7–10 days postinfection before adaptive immune responses emerge. The innate immune response is important for CHIKV clearance.

Results

The effects of Poly (I:C) on the replication of CHIKV in human bronchial epithelial cells, BEAS-2B, were studied. Poly (I:C) suppressed cytopathic effects (CPE) induced by CHIKV infection in BEAS-2B cells in the presence of Poly (I:C) and inhibited the replication of CHIKV in the cells. The virus titers of Poly (I:C)-treated cells were much lower compared with those of untreated cells. CHIKV infection and Poly (I:C) treatment of BEAS-2B cells induced the production of IFN-β and increased the expression of anti-viral genes, including IFN-α, IFN-β, MxA, and OAS. Both Poly (I:C) and CHIKV infection upregulate the expression of TLR3 in BEAS-2B cells.

Conclusions

CHIKV is sensitive to innate immune response induced by Poly (I:C). The inhibition of CHIKV replication by Poly (I:C) may be through the induction of TLR3, which triggers the production of IFNs and other anti-viral genes. The innate immune response is important to clear CHIKV in infected cells.

Neutralization titers against influenza A (H3N2) and influenza B viruses among a non-vaccinated population from Thailand

Influenza A and B viruses are viral respiratory pathogens that can cause severe infections among birds and mammals. Neutralization assays using human sera are useful to evaluate the risk of circulating viruses to humans. In this study, 359 serum samples from healthy Thai volunteers, who had not been vaccinated against influenza for at least five years, were investigated by microneutralization (MN) assays against influenza A H3N2 and influenza B viruses in 2009. There was no significant difference in neutralization activities against 2006 and 2008 isolates of influenza A H3N2 viruses. However, neutralization titers to influenza B viruses among 2008 isolates were quite low. The results indicate the non-vaccinated study population had some neutralizing antibodies against influenza A H3N2 but not against influenza B viruses.

Tropism of Pandemic 2009 H1N1 Influenza a Virus

Substitutions at the receptor-binding site of the pandemic H1N1 2009 influenza A virus (H1N1pdm) hemagglutinin (HA) gene may be critical in determining whether a virus binds to human or avian receptors. Previous reports suggest that HA Gly²²² and/or Arg²²³ allow viruses to bind preferentially to the α2,3-linked sialic acid found in avian species. We also demonstrated that serial passaging of influenza A virus in embryonated chicken eggs increased viral growth 32- to 64-fold, coincident with the increased prevalence of Gly²²² or Arg²²³ in HA protein (Yasugi et al., 2012). In this study, we showed that the minor genotype of α2,3-linkage-tropic viruses in upper airways became dominant after passaging through chicken eggs. Viruses possessing HA containing N125D-Q223R, N125D-D187E-Q223R, K119N-D222G, and K119N-N129S-D222G, were detected in both clinical specimens and egg-passaged samples. These results might suggest that egg-adapted viruses, likely represented by α2,3-linkage-tropic virus, were also present in human upper airways as a minor population and transmitted in humans during the outbreak of H1N1pdm.

Detection of influenza virus using a lateral flow immunoassay for amplified DNA by a microfluidic RT-PCR chip

Influenza virus RNA was amplified by a continuous-flow polydimethylsiloxane microfluidic RT-PCR chip within 15-20 min. The amplified influenza virus RNA was observed with the naked eye, as the red color at the test line, using a lateral flow immunoassay within 1 min.

Decompression procedure using a microendoscopic technique for thoracic myelopathy caused by ossification of the ligamentum flavum

BACKGROUND

Microendoscopic discectomy (MED) is one of the minimally invasive endoscopic procedures for treating lumbar disc herniation. The aim of this case report is to describe a patient with thoracic ossification of the ligamentum flavum (OLF) that was completely removed using the microendoscopic technique.

CASE REPORT

We report on a 62-year-old male patient who presented with thoracic myelopathy caused by OLF at the Th11-12. A posterior decompression via spinous process splitting approach using the microendoscopic technique at the Th11-12 was performed. The bilateral ossified ligamentum flavum could be en bloc removed separately. A sufficient decompression of the spinal cord and the spinal canal with no evidence of damage on the paraspinal muscles was demonstrated on magnetic resonance images after surgery. The patient's neurological symptoms were alleviated at 24 months after surgery. There was no evidence of postoperative instability at the final follow-up.

CONCLUSION

The authors found that the microendoscopic technique could be applied to decompression surgery for thoracic OLF. The procedure could provide a sufficient decompression with minimum damage to the paraspinal muscles. However, the microendoscopic procedure should be indicated only for select thoracic OLF, such as OLF without fusion at the middle of the spinal canal and OLF without dural ossification, because of its technical difficulties.

Hepatitis E virus in Norway rats (Rattus norvegicus) captured around a pig farm

Background

Hepatitis E virus (HEV) transmitted via the oral route through the consumption of contaminated water or uncooked or undercooked contaminated meat has been implicated in major outbreaks. Rats may play a critical role in HEV outbreaks, considering their negative effects on environmental hygiene and food sanitation. Although the serological evidence of HEV infection in wild rodents has been reported worldwide, the infectivity and propagation of HEV in wild rats remain unknown. To investigate if rats are a possible carrier of HEV, we studied wild Norway rats (Rattus norvegicus) that were caught near a pig farm, where HEV was prevalent among the pigs.

Methods

We examined 56 Norway rats for HEV. RNA from internal organs was examined for RT-PCR and positive samples were sequenced. Positive tissue samples were incubated with A549 cell line to isolate HEV. Anti-HEV antibodies were detected by ELISA.

Results

Sixteen rats were seropositive, and the HEV RNA was detected in 10 of the 56 rats. Sequencing of the partial ORF1 gene from 7 samples resulted in partially sequenced HEV, belonging to genotype 3, which was genetically identical to the HEV prevalent in the swine from the source farm. The infectious HEVs were isolated from the Norway rats by using the human A549 cell line.

Conclusions

There was a relatively high prevalence (17.9%) of the HEV genome in wild Norway rats. The virus was mainly detected in the liver and spleen. The results indicate that these animals might be possible carrier of swine HEV in endemic regions. The HEV contamination risk due to rats needs to be examined in human habitats.

The changing nature of avian influenza A virus (H5N1)

Highly pathogenic avian influenza A virus subtype H5N1 has been endemic in some bird species since its emergence in 1996 and its ecology, genetics and antigenic properties have continued to evolve. This has allowed diverse virus strains to emerge in endemic areas with altered receptor specificity, including a new H5 sublineage with enhanced binding affinity to the human-type receptor. The pandemic potential of H5N1 viruses is alarming and may be increasing. We review here the complex dynamics and changing nature of the H5N1 virus that may contribute to the emergence of pandemic strains.

Molecular evolution of HIV-1 CRF01_AE Env in Thai patients

Background

The envelope glycoproteins (Env), gp120 and gp41, are the most variable proteins of human immunodeficiency virus type 1 (HIV-1), and are the major targets of humoral immune responses against HIV-1. A circulating recombinant form of HIV-1, CRF01_AE, is prevalent throughout Southeast Asia; however, only limited information regarding the immunological characteristics of CRF01_AE Env is currently available. In this study, we attempted to examine the evolutionary pattern of CRF01_AE Env under the selection pressure of host immune responses.

Methodology/Principal Findings

Peripheral blood samples were collected periodically over 3 years from 15 HIV-1-infected individuals residing in northern Thailand, and amplified env genes from the samples were subjected to computational analysis. The V5 region of gp120 showed highest variability in several samples over 3 years, whereas the V1/V2 and/or V4 regions of gp120 also showed high variability in many samples. In addition, the N-terminal part of the C3 region of gp120 showed highest amino acid diversity among the conserved regions of gp120. Chronological changes in the numbers of amino acid residues in gp120 variable regions and potential N-linked glycosylation (PNLG) sites are involved in increasing the variability of Env gp120. Furthermore, the C3 region contained several amino acid residues potentially under positive selection, and APOBEC3 family protein-mediated G to A mutations were frequently detected in such residues.

Conclusions/Significance

Several factors, including amino acid substitutions particularly in gp120 C3 and V5 regions as well as changes in the number of PNLG sites and in the length of gp120 variable regions, were revealed to be involved in the molecular evolution of CRF01_AE Env. In addition, a similar tendency was observed between CRF01_AE and subtype C Env with regard to the amino acid variation of gp120 V3 and C3 regions. These results may provide important information for understanding the immunological characteristics of CRF01_AE Env.

Dengue virus presence and surveillance in Okinawa (Review)

Recent reports have shown that the dengue virus (DENV) is a serious concern worldwide, especially in subtropical areas such as South-East Asia. With the development of transportation systems, the risk of DENV infection spreading is increasing. Since mosquitoes transmit DENV to humans, surveillance of DENV-infected mosquito vectors is the most effective approach for preventing DENV. Okinawa is the only prefecture located in a subtropical region in Japan and historically shows continuous importation of DENV-related mosquito vectors. In this review, we describe the current and historical status of DENV in Okinawa.

Analysis of intracellular distribution of Borna disease virus glycoprotein fused with fluorescent markers in living cells

Borna disease virus (BDV) is a non-segmented, negative-strand RNA virus that is characterized by nuclear replication and persistent infection. A unique feature of BDV is that it releases only a small number of infectious particles from infected cells. Although these characteristics might make it difficult to obtain a large amount of recombinant viruses in a reverse genetics system, the mechanism underlying the budding or assembly of BDV particle has remained largely unknown. In this study, as a first step toward understanding the virion formation of BDV, we investigated the intracellular distribution and mobility of the fluorescent marker fusion envelope glycoprotein (G) of BDV in living cells. Expression analysis revealed that fusion proteins seem to cleave into functional subunits and localize in the endoplasmic reticulum (ER)/Golgi apparatus, as well as the authentic BDV G. Furthermore, we demonstrated using fluorescence recovery after photobleaching analysis that BDV G fluorescence shows rapid recovery in both the ER/Golgi and plasma membrane regions, indicating that BDV G fusion protein may be a useful tool to investigate not only the maturation of BDV G but also the budding and assembly of BDV particles in living cells.

Variability of parvovirus B19 genotype 2 in plasma products with different compositions in the inactivation sensitivity by liquid-heating

BACKGROUND AND OBJECTIVES

Our previous report showed that parvovirus B19 genotype 1 in different solutions derived from plasma preparations showed different heat-sensitivity patterns during liquid-heating. In this study, we similarly examined B19 genotype 2.

MATERIALS AND METHODS

Two plasma samples one containing B19 genotype 1 and the other genotype 2 DNA were used. Four process samples collected immediately before the heat treatment step in the manufacture of albumin, immunoglobulin, haptoglobin and antithrombin preparations were spiked with B19 and subsequently treated at 60°C for 10 h. A low pH immunoglobulin solution was also spiked with B19 and treated at room temperature for 14 days. Infectivity was then measured.

RESULTS

B19 genotype 2, similar to genotype 1, showed three patterns of inactivation: (i) a rapid inactivation in the albumin and immunoglobulin preparations, (ii) a slow inactivation in the haptoglobin preparation and (iii) only limited inactivation in the antithrombin preparation. Its sensitivity in the low pH immunoglobulin solutions also resembled that of genotype 1.

CONCLUSION

Both genotypes 1 and 2 of B19 varied in sensitivity to liquid-heating and low pH among different plasma preparations.

Capture of dengue virus type 3 using anionic polymer-coated magnetic beads

Dengue virus (DENV) is a mosquito-borne virus and can be transmitted to humans by mosquito vectors. Although surveillance of dengue virus-infected mosquitoes is the most effective way of controlling DENV infections, detection of DENVs in mosquitoes is limited by the low sensitivity of available detection methods. We here report a method for capturing DENV type 3 (DENV-3) from mosquito cells using magnetic beads coated with an anionic polymer, poly(methyl vinyl ether-maleic anhydrate). The beads were incubated with cell culture medium of DENV-3-infected mosquito cells, then separated from the supernatant by applying a magnetic field and washed. Adsorption of DENV-3 on the beads was confirmed by reverse transcription-polymerase chain reaction, which detected the presence of DENV-3 genomic RNA on the beads, and Western blotting, which determined the major DENV-3 envelope protein on the beads. Therefore, this capture method may enable an improvement in DENV-3 detection.

Genetic diversification of H5N1 highly pathogenic avian influenza A virus during replication in wild ducks

Highly pathogenic avian influenza A virus subtype H5N1 can potentially generate novel variants during replication of infected hosts. To determine which H5N1 variants predominate in wild birds, we determined the sequences of RT-PCR amplified viral genes from several organs of infected chickens and ducks from Egypt, where H5N1 outbreaks in birds are endemic. Comparison of the sequences in viruses from trachea, lung, brain and liver revealed diversification with different amino acid substitutions in different ducks, but no diversification in chickens. These specific amino acid substitutions were rare among viruses currently circulating in Egypt. In addition, the H5N1 variants showed distinct growth kinetics in duck, canine and human cells. Our findings suggested that ducks can generate H5N1 variants with novel amino acid substitutions that might serve as aetiological agents for new influenza virus outbreaks and epidemics.

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

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.