Pranee Thawatsupha

Avian Influenza (H5N1) Viruses Isolated from Humans in Asia in 2004 Exhibit Increased Virulence in Mammals

ABSTRACT The spread of highly pathogenic avian influenza H5N1 viruses across Asia in 2003 and 2004 devastated domestic poultry populations and resulted in the largest and most lethal H5N1 virus outbreak in humans to date. To better understand the potential of H5N1 viruses isolated during this epizootic event to cause disease in mammals, we used the mouse and ferret models to evaluate the relative virulence of selected 2003 and 2004 H5N1 viruses representing multiple genetic and geographical groups and compared them to earlier H5N1 strains isolated from humans. Four of five human isolates tested were highly lethal for both mice and ferrets and exhibited a substantially greater level of virulence in ferrets than other H5N1 viruses isolated from humans since 1997. One human isolate and all four avian isolates tested were found to be of low virulence in either animal. The highly virulent viruses replicated to high titers in the mouse and ferret respiratory tracts and spread to multiple organs, including the brain. Rapid disease progression and high lethality rates in ferrets distinguished the highly virulent 2004 H5N1 viruses from the 1997 H5N1 viruses. A pair of viruses isolated from the same patient differed by eight amino acids, including a Lys/Glu disparity at 627 of PB2, previously identified as an H5N1 virulence factor in mice. The virus possessing Glu at 627 of PB2 exhibited only a modest decrease in virulence in mice and was highly virulent in ferrets, indicating that for this virus pair, the K627E PB2 difference did not have a prevailing effect on virulence in mice or ferrets. Our results demonstrate the general equivalence of mouse and ferret models for assessment of the virulence of 2003 and 2004 H5N1 viruses. However, the apparent enhancement of virulence of these viruses in humans in 2004 was better reflected in the ferret.

Highly Pathogenic Avian Influenza H5N1 Viruses Elicit an Attenuated Type I Interferon Response in Polarized Human Bronchial Epithelial Cells

ABSTRACT The unparalleled spread of highly pathogenic avian influenza A (HPAI) H5N1 viruses has resulted in devastating outbreaks in domestic poultry and sporadic human infections with a high fatality rate. To better understand the mechanism(s) of H5N1 virus pathogenesis and host responses in humans, we utilized a polarized human bronchial epithelial cell model that expresses both avian alpha-2,3- and human alpha-2,6-linked sialic acid receptors on the apical surface and supports productive replication of both H5N1 and H3N2 viruses. Using this model, we compared the abilities of selected 2004 HPAI H5N1 viruses isolated from humans and a recent human H3N2 virus to trigger the type I interferon (IFN) response. H5N1 viruses elicited significantly less IFN regulatory factor 3 (IRF3) nuclear translocation, as well as delayed and reduced production of IFN-β compared with the H3N2 virus. Furthermore, phosphorylation of Stat2 and induction of IFN-stimulated genes (ISGs), such as MX1, ISG15, IRF7, and retinoic acid-inducible gene I, were substantially delayed and reduced in cells infected with H5N1 viruses. We also observed that the highly virulent H5N1 virus replicated more efficiently and induced a weaker IFN response than the H5N1 virus that exhibited low virulence in mammals in an earlier study. Our data suggest that the H5N1 viruses tested, especially the virus with the high-pathogenicity phenotype, possess greater capability to attenuate the type I IFN response than the human H3N2 virus. The attenuation of this critical host innate immune defense may contribute to the virulence of H5N1 viruses observed in humans.

ATYPICAL AVIAN INFLUENZA (H5N1)

We report the first case of avian influenza in a patient with fever and diarrhea but no respiratory symptoms. Avian influenza should be included in the differential diagnosis for patients with predominantly gastrointestinal symptoms, particularly if they have a history of exposure to poultry.

Seroprevalence of Anti-H5 Antibody among Thai Health Care Workers after Exposure to Avian Influenza (H5N1) in a Tertiary Care Center

After the initial atypical presentation of a patient with avian influenza (H5N1) infection, paired acute-phase and convalescent-phase serum samples obtained from 25 health care workers (HCWs) who were exposed to the patient were compared with paired serum samples obtained from 24 HCWs who worked at different units in the same hospital and were not exposed to the patient. There was no serologic evidence of anti-H5 antibody reactivity or subclinical infection in either of the groups.

Higher in vitro susceptibility of human T cells to H5N1 than H1N1 influenza viruses

Patients infected with H5N1 influenza A virus, who had a severe or fatal outcome, exhibited several characteristic clinical manifestations including lymphopenia. In this study, human CD4(+) T-cell lines and healthy donor-derived peripheral blood mononuclear cells (PBMCs) were examined for susceptibility to infection with Thai isolates of H5N1 in comparison to those of H1N1. Although cellular levels were variable between H5N1 and H1N1 in T-cell lines and PBMCs, rates of production of progeny virions were significantly higher in H5N1 infections, suggesting a more efficient release of virions. In addition, cytopathogenicity in PBMCs, leading to a decline in CD4(+) T-cell numbers, were much severer with H5N1 than H1N1. Thus, human T cells could be an important target for infection with H5N1.