Efficacy of oseltamivir therapy in ferrets inoculated with different clades of H5N1 influenza virus.

Highly pathogenic H5N1 influenza viruses have infected an increasing number of humans in Asia, with high mortality rates and the emergence of multiple distinguishable clades. It is not known whether antiviral drugs that are effective against contemporary human influenza viruses will be effective against systemically replicating viruses, such as these pathogens. Therefore, we evaluated the use of the neuraminidase (NA) inhibitor oseltamivir for early postexposure prophylaxis and for treatment in ferrets exposed to representatives of two clades of H5N1 virus with markedly different pathogenicities in ferrets.

Emergence of influenza A virus variants after prolonged shedding from pheasants.

We previously demonstrated the susceptibility of pheasants to infection with influenza A viruses of 15 hemagglutinin (HA) subtypes: 13/23 viruses tested were isolated for >or=14 days, all in the presence of serum-neutralizing antibodies; one virus (H10) was shed for 45 days postinfection. Here we confirmed that 20% of pheasants shed low-pathogenic influenza viruses for prolonged periods. We aimed to determine why the antibody response did not clear the virus in the usual 3 to 10 days, because pheasants serve as a long-term source of influenza viruses in poultry markets.

H5N1 influenza viruses in Lao People's Democratic Republic.

A prospective surveillance program for influenza viruses was established in Lao People's Democratic Republic (PDR) in July of 2005. We report isolation of H5N1 virus genetically distinct from H5N1 circulating in 2004, which indicates reintroduction of H5N1 into Lao PDR after its disappearance (i.e.

Continuing evolution of H9 influenza viruses in Korean poultry.

We analyzed the evolution of H9 influenza viruses isolated from Korean chicken farms from 2002 to 2004. Korean H9 viruses formed two antigenically distinct groups: those isolated from 1996 to mid-2003, and those isolated from late 2003 through 2004. Most of the 2004 isolates showed greater cross-reactivity with the second group than with the first group.

Cross-protectiveness and immunogenicity of influenza A/Duck/Singapore/3/97(H5) vaccines against infection with A/Vietnam/1203/04(H5N1) virus in ferrets.

Ferrets were immunized with two 7- mu g doses of hemagglutinin from inactivated whole-virus vaccines containing the hemagglutinin gene of A/Duck/Singapore/3/97(H5N3) then inoculated with a lethal dose of A/Vietnam/1203/04(H5N1) (Viet/1203/04). Serum samples did not react with Viet/1203/04 in hemagglutination-inhibition (HI) or virus-neutralization (VN) tests. All vaccinated ferrets survived the challenge, whereas all mock-immunized ferrets died.

Importance of neuraminidase active-site residues to the neuraminidase inhibitor resistance of influenza viruses.

Neuraminidase inhibitors (NAIs) are antivirals designed to target conserved residues at the neuraminidase (NA) enzyme active site in influenza A and B viruses. The conserved residues that interact with NAIs are under selective pressure, but only a few have been linked to resistance. In the A/Wuhan/359/95 (H3N2) recombinant virus background, we characterized seven charged, conserved NA residues (R118, R371, E227, R152, R224, E276, and D151) that directly interact with the NAIs but have not been reported to confer resistance to NAIs.

Detection of influenza viruses resistant to neuraminidase inhibitors in global surveillance during the first 3 years of their use.

Emergence of influenza viruses with reduced susceptibility to neuraminidase inhibitors (NAIs) develops at a low level following drug treatment, and person-to-person transmission of resistant virus has not been recognized to date. The Neuraminidase Inhibitor Susceptibility Network (NISN) was established to follow susceptibility of isolates and occurrence of NAI resistance at a population level in various parts of the world. Isolates from the WHO influenza collaborating centers were screened for susceptibilities to oseltamivir and zanamivir by a chemiluminescent enzyme inhibition assay, and those considered potentially resistant were analyzed by sequence analysis of the neuraminidase genes.

Characterization of an avian influenza virus of subtype H7N2 isolated from chickens in northern China.

An H7N2 avian influenza virus was isolated from chickens during routine surveillance in northern China in 2002. To understand the origin of this virus, we completely sequenced its genome. The PB1, PA, HA, and M genes of this virus were highly homologous with those of the wild bird virus A/Africa starling/Eng-Q/983/79 (H7N1).

Domestic ducks and H5N1 influenza epidemic, Thailand.

In addition to causing 12 human deaths and 17 cases of human infection, the 2004 outbreak of H5N1 influenza virus in Thailand resulted in the death or slaughter of 60 million domestic fowl and the disruption of poultry production and trade. After domestic ducks were recognized as silent carriers of H5N1 influenza virus, government teams went into every village to cull flocks in which virus was detected; these team efforts markedly reduced H5N1 infection. Here we examine the pathobiology and epidemiology of H5N1 influenza virus in the 4 systems of duck raising used in Thailand in 2004.

Distribution of amantadine-resistant H5N1 avian influenza variants in Asia.

We examined the distribution of genetic mutations associated with resistance to the M2 ion channel-blocking adamantane derivatives, amantadine and rimantadine, among H5N1 viruses isolated in Vietnam, Thailand, Cambodia, Indonesia, Hong Kong, and China. More than 95% of the viruses isolated in Vietnam and Thailand contained resistance mutations, but resistant mutants were less commonly isolated in Indonesia (6.3% of isolates) and China (8.

The immunogenicity and efficacy against H5N1 challenge of reverse genetics-derived H5N3 influenza vaccine in ducks and chickens.

H5N1 avian influenza viruses are continuing to spread in waterfowl in Eurasia and to threaten the health of avian and mammalian species. The possibility that highly pathogenic (HP) H5N1 avian influenza is now endemic in both domestic and migratory birds in Eurasia makes it unlikely that culling alone will control H5N1 influenza. Because ducks are not uniformly killed by HP H5N1 viruses, they are considered a major contributor to virus spread.

Gangliosides are not essential for influenza virus infection.

Sialic acid is known to be an essential part of influenza virus receptors, but the specific identity of the receptor molecules on target cells is still not defined. In particular, the relative roles played by cellular sialylglycoproteins and gangliosides in virus entry into target cells remain unclear. To test whether gangliosides are essential for virus infection, we used the GM-95 mutant cell line of mouse B16 melanoma which lacks synthesis of major glycosphingolipids including gangliosides.

Molecular changes associated with adaptation of human influenza A virus in embryonated chicken eggs.

Failure to isolate A/Fujian/411/2002 (H3N2) in embryonated chicken eggs resulted in its absence from the 2003/2004 vaccine. We analyzed the adaptation of this virus in eggs during serial passages in the amniotic then allantoic cavities. Amniotic passage allowed the virus to grow in the allantoic cavity.

The polymerase complex genes contribute to the high virulence of the human H5N1 influenza virus isolate A/Vietnam/1203/04.

H5N1 influenza viruses transmitted from poultry to humans in Asia cause high mortality and pose a pandemic threat. Viral genes important for cell tropism and replication efficiency must be identified to elucidate and target virulence factors. We applied reverse genetics to generate H5N1 reassortants combining genes of lethal A/Vietnam/1203/04 (VN1203), a fatal human case isolate, and nonlethal A/chicken/Vietnam/C58/04 (CH58) and tested their pathogenicity in ferrets and mice.

Combination chemotherapy, a potential strategy for reducing the emergence of drug-resistant influenza A variants.

Rapid development of resistant influenza variants after amantadine treatment is one of the main drawbacks of M2 blockers. On the other hand, the emergence of variants with low susceptibility to the neuraminidase (NA) inhibitors is limited. In the present study we examined whether combination therapy with two classes of anti-influenza drugs can affect the emergence of resistant variants in vitro.

H5N1 outbreaks and enzootic influenza.

Ongoing outbreaks of H5N1 avian influenza in migratory waterfowl, domestic poultry, and humans in Asia during the summer of 2005 present a continuing, protean pandemic threat. We review the zoonotic source of highly pathogenic H5N1 viruses and their genesis from their natural reservoirs. The acquisition of novel traits, including lethality to waterfowl, ferrets, felids, and humans, indicates an expanding host range.

Comparison of the replication of influenza A viruses in Chinese ring-necked pheasants and chukar partridges.

We investigated the replication and transmission of avian influenza A viruses in two species thought to be intermediate hosts in the spread of influenza A viruses in live poultry markets: Chinese ring-necked pheasants and chukar partridges. All 15 hemagglutinin subtypes replicated in pheasants, and most subtypes transmitted to naïve contact pheasants, primarily via the fecal-oral route. Many viruses were shed from the gastrointestinal tract of experimentally inoculated pheasants for 14 days or longer.

Large-scale sequence analysis of avian influenza isolates.

The spread of H5N1 avian influenza viruses (AIVs) from China to Europe has raised global concern about their potential to infect humans and cause a pandemic. In spite of their substantial threat to human health, remarkably little AIV whole-genome information is available. We report here a preliminary analysis of the first large-scale sequencing of AIVs, including 2196 AIV genes and 169 complete genomes.

Neuraminidase inhibitor susceptibility network position statement: antiviral resistance in influenza A/H5N1 viruses.

The emerging epidemic of H5N1 avian influenza virus with spillover into the human population in Asia has provoked intense concern globally about the potential of these particularly pathogenic viruses to evolve with the capacity for human-to-human transmission with a consequent pandemic. The availability of antiviral drugs with activity against influenza A viruses and the recognition of drug-resistant variants to these drugs prompted the following report by a select group of the global experts--members of the Neuraminidase Inhibitor Susceptibility Network--on the best use of the available drugs, both for prophylaxis and treatment. The editors of Antiviral Therapy are pleased to be able to provide this document in an expeditious manner.

Human infection with an avian H9N2 influenza A virus in Hong Kong in 2003.

Avian H9N2 influenza A virus has caused repeated human infections in Asia since 1998. Here we report that an H9N2 influenza virus infected a 5-year-old child in Hong Kong in 2003. To identify the possible source of the infection, the human isolate and other H9N2 influenza viruses isolated from Hong Kong poultry markets from January to October 2003 were genetically and antigenically characterized.

The genesis of a pandemic influenza virus.

Pandemic influenza viruses pose a significant threat to public health worldwide. In a recent Nature paper, Taubenberger et al. (2005) now report remarkable similarities between the polymerase genes of the influenza virus that caused the 1918 Spanish influenza pandemic and those of avian influenza viruses.

Neuraminidase inhibitor-resistant influenza viruses may differ substantially in fitness and transmissibility.

Mutations of the conserved residues of influenza virus neuraminidase (NA) that are associated with NA inhibitor (NAI) resistance decrease the sialidase activity and/or stability of the NA, thus compromising viral fitness. In fact, clinically derived NAI-resistant variants with different NA mutations have shown different transmissibilities in ferrets (M. L.

Restoration of virulence of escape mutants of H5 and H9 influenza viruses by their readaptation to mice.

Antigenic mapping of the haemagglutinin (HA) molecule of H5 and H9 influenza viruses by selecting escape mutants with monoclonal anti-HA antibodies and subjecting the selected viruses to immunological analysis and sequencing has previously been performed. The viruses used as wild-type strains were mouse-adapted variants of the original H5 and H9 isolates. Phenotypic characterization of the escape mutants revealed that the amino acid change in HA that conferred resistance to a monoclonal antibody was sometimes associated with additional effects, including decreased virulence for mice.