Judith M. A. van den Brand

Pathogenesis and transmission of swine-origin 2009 A(H1N1) influenza virus in ferrets

“Swine Flu” Pathology The clinical spectrum of disease caused by the swine-origin 2009 A(H1N1) influenza virus and its transmissibility are not completely understood. Munster et al. (p. 481; published online 2 July) and Maines et al. (p. 484; published online 2 July) used ferrets, an established model for human influenza, to evaluate the pathogenesis and transmissibility of a selection of 2009 A(H1N1) virus isolates compared with representative seasonal H1N1 viruses. The results help explain the atypical symptoms seen so far, including the gastrointestinal distress and vomiting observed in many patients. Although results were variable, it seems that the 2009 A(H1N1) virus may be less efficiently transmitted by respiratory droplets in comparison to the highly transmissible seasonal H1N1 virus, suggesting that additional virus adaptation in mammals may be required before we see phenotypes observed in earlier pandemics. Animal experiments compare the dynamics and effects of the virus causing the 2009 flu outbreak to those of seasonal H1N1 flu. The swine-origin A(H1N1) influenza virus that has emerged in humans in early 2009 has raised concerns about pandemic developments. In a ferret pathogenesis and transmission model, the 2009 A(H1N1) influenza virus was found to be more pathogenic than a seasonal A(H1N1) virus, with more extensive virus replication occurring in the respiratory tract. Replication of seasonal A(H1N1) virus was confined to the nasal cavity of ferrets, but the 2009 A(H1N1) influenza virus also replicated in the trachea, bronchi, and bronchioles. Virus shedding was more abundant from the upper respiratory tract for 2009 A(H1N1) influenza virus as compared with seasonal virus, and transmission via aerosol or respiratory droplets was equally efficient. These data suggest that the 2009 A(H1N1) influenza virus has the ability to persist in the human population, potentially with more severe clinical consequences.

Limited airborne transmission of H7N9 influenza A virus between ferrets

Wild waterfowl form the main reservoir of influenza A viruses, from which transmission occurs directly or indirectly to various secondary hosts, including humans. Direct avian-to-human transmission has been observed for viruses of subtypes A(H5N1), A(H7N2), A(H7N3), A(H7N7), A(H9N2) and A(H10N7) upon human exposure to poultry, but a lack of sustained human-to-human transmission has prevented these viruses from causing new pandemics. Recently, avian A(H7N9) viruses were transmitted to humans, causing severe respiratory disease and deaths in China. Because transmission via respiratory droplets and aerosols (hereafter referred to as airborne transmission) is the main route for efficient transmission between humans, it is important to gain an insight into airborne transmission of the A(H7N9) virus. Here we show that although the A/Anhui/1/2013 A(H7N9) virus harbours determinants associated with human adaptation and transmissibility between mammals, its airborne transmissibility in ferrets is limited, and it is intermediate between that of typical human and avian influenza viruses. Multiple A(H7N9) virus genetic variants were transmitted. Upon ferret passage, variants with higher avian receptor binding, higher pH of fusion, and lower thermostability were selected, potentially resulting in reduced transmissibility. This A(H7N9) virus outbreak highlights the need for increased understanding of the determinants of efficient airborne transmission of avian influenza viruses between mammals.

Severity of Pneumonia Due to New H1N1 Influenza Virus in Ferrets Is Intermediate between That Due to Seasonal H1N1 Virus and Highly Pathogenic Avian Influenza H5N1 Virus

Abstract Background. The newly emerged influenza A(H1N1) virus (new H1N1 virus) is causing the first influenza pandemic of this century. Three influenza pandemics of the previous century caused variable mortality, which largely depended on the development of severe pneumonia. However, the ability of the new H1N1 virus to cause pneumonia is poorly understood. Methods. The new H1N1 virus was inoculated intratracheally into ferrets. Its ability to cause pneumonia was compared with that of seasonal influenza H1N1 virus and highly pathogenic avian influenza (HPAI) H5N1 virus by using clinical, virological, and pathological analyses. Results. Our results showed that the new H1N1 virus causes pneumonia in ferrets intermediate in severity between that caused by seasonal H1N1 virus and by HPAI H5N1 virus. The new H1N1 virus replicated well throughout the lower respiratory tract and more extensively than did both seasonal H1N1 virus (which replicated mainly in the bronchi) and HPAI H5N1 virus (which replicated mainly in the alveoli). High loads of new H1N1 virus in lung tissue were associated with diffuse alveolar damage and mortality. Conclusions. The new H1N1 virus may be intrinsically more pathogenic for humans than is seasonal H1N1 virus.

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

ABSTRACT The continuous circulation of the highly pathogenic avian influenza (HPAI) H5N1 virus has been a cause of great concern. The possibility of this virus acquiring specificity for the human influenza A virus receptor, α2,6-linked sialic acids (SA), and being able to transmit efficiently among humans is a constant threat to human health. Different studies have described amino acid substitutions in hemagglutinin (HA) of clinical HPAI H5N1 isolates or that were introduced experimentally that resulted in an increased, but not exclusive, binding of these virus strains to α2,6-linked SA. We introduced all previously described amino acid substitutions and combinations thereof into a single genetic background, influenza virus A/Indonesia/5/05 HA, and tested the receptor specificity of these 27 mutant viruses. The attachment pattern to ferret and human tissues of the upper and lower respiratory tract of viruses with α2,6-linked SA receptor preference was then determined and compared to the attachment pattern of a human influenza A virus (H3N2). At least three mutant viruses showed an attachment pattern to the human respiratory tract similar to that of the human H3N2 virus. Next, the replication efficiencies of these mutant viruses and the effects of three different neuraminidases on virus replication were determined. These data show that influenza virus A/Indonesia/5/05 potentially requires only a single amino acid substitution to acquire human receptor specificity, while at the same time remaining replication competent, thus suggesting that the pandemic threat posed by HPAI H5N1 is far from diminished.

Metagenomic analysis of the viral flora of pine marten and European badger feces

ABSTRACT A thorough understanding of the diversity of viruses in wildlife provides epidemiological baseline information about potential pathogens. Metagenomic analysis of the enteric viral flora revealed a new anellovirus and bocavirus species in pine martens and a new circovirus-like virus and geminivirus-related DNA virus in European badgers. In addition, sequences with homology to viruses from the families Paramyxo- and Picornaviridae were detected.

Vaccination against human influenza A/H3N2 virus prevents the induction of heterosubtypic immunity against lethal infection with avian influenza A/H5N1 virus.

Annual vaccination against seasonal influenza viruses is recommended for certain individuals that have a high risk for complications resulting from infection with these viruses. Recently it was recommended in a number of countries including the USA to vaccinate all healthy children between 6 and 59 months of age as well. However, vaccination of immunologically naïve subjects against seasonal influenza may prevent the induction of heterosubtypic immunity against potentially pandemic strains of an alternative subtype, otherwise induced by infection with the seasonal strains. Here we show in a mouse model that the induction of protective heterosubtypic immunity by infection with a human A/H3N2 influenza virus is prevented by effective vaccination against the A/H3N2 strain. Consequently, vaccinated mice were no longer protected against a lethal infection with an avian A/H5N1 influenza virus. As a result H3N2-vaccinated mice continued to loose body weight after A/H5N1 infection, had 100-fold higher lung virus titers on day 7 post infection and more severe histopathological changes than mice that were not protected by vaccination against A/H3N2 influenza. The lack of protection correlated with reduced virus-specific CD8+ T cell responses after A/H5N1 virus challenge infection. These findings may have implications for the general recommendation to vaccinate all healthy children against seasonal influenza in the light of the current pandemic threat caused by highly pathogenic avian A/H5N1 influenza viruses.

An orthopoxvirus-based vaccine reduces virus excretion after MERS-CoV infection in dromedary camels

Coronaviruses in the Middle East Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe acute respiratory illness and kills about a third of people infected. The virus is common in dromedary camels, which can be a source of human infections. In a survey for MERSCoV in over 1300 Saudi Arabian camels, Sabir et al. found that dromedaries share three coronavirus species with humans. Diverse MERS lineages in camels have caused human infections, which suggests that transfer among host species occurs quite easily. Haagmans et al. made a MERS-CoV vaccine for use in camels, using poxvirus as a vehicle. The vaccine significantly reduced virus excretion, which should help reduce the potential for transmission to humans, and conferred cross-immunity to camelpox infections. Science, this issue p. 81, p. 77 A camel vaccine against MERS coronavirus may reduce the risk of human infection and protect against camelpox too. Middle East respiratory syndrome coronavirus (MERS-CoV) infections have led to an ongoing outbreak in humans, which was fueled by multiple zoonotic MERS-CoV introductions from dromedary camels. In addition to the implementation of hygiene measures to limit further camel-to-human and human-to-human transmissions, vaccine-mediated reduction of MERS-CoV spread from the animal reservoir may be envisaged. Here we show that a modified vaccinia virus Ankara (MVA) vaccine expressing the MERS-CoV spike protein confers mucosal immunity in dromedary camels. Compared with results for control animals, we observed a significant reduction of excreted infectious virus and viral RNA transcripts in vaccinated animals upon MERS-CoV challenge. Protection correlated with the presence of serum neutralizing antibodies to MERS-CoV. Induction of MVA-specific antibodies that cross-neutralize camelpox virus would also provide protection against camelpox.

Adenosine Deaminase Acts as a Natural Antagonist for Dipeptidyl Peptidase 4 Mediated Entry of the Middle East Respiratory Syndrome Coronavirus

ABSTRACT Middle East respiratory syndrome coronavirus (MERS-CoV) replicates in cells of different species using dipeptidyl peptidase 4 (DPP4) as a functional receptor. Here we show the resistance of ferrets to MERS-CoV infection and inability of ferret DDP4 to bind MERS-CoV. Site-directed mutagenesis of amino acids variable in ferret DPP4 thus revealed the functional human DPP4 virus binding site. Adenosine deaminase (ADA), a DPP4 binding protein, competed for virus binding, acting as a natural antagonist for MERS-CoV infection.

Exacerbated innate host response to SARS-CoV in aged non-human primates

The emergence of viral respiratory pathogens with pandemic potential, such as severe acute respiratory syndrome coronavirus (SARS-CoV) and influenza A H5N1, urges the need for deciphering their pathogenesis to develop new intervention strategies. SARS-CoV infection causes acute lung injury (ALI) that may develop into life-threatening acute respiratory distress syndrome (ARDS) with advanced age correlating positively with adverse disease outcome. The molecular pathways, however, that cause virus-induced ALI/ARDS in aged individuals are ill-defined. Here, we show that SARS-CoV-infected aged macaques develop more severe pathology than young adult animals, even though viral replication levels are similar. Comprehensive genomic analyses indicate that aged macaques have a stronger host response to virus infection than young adult macaques, with an increase in differential expression of genes associated with inflammation, with NF-κB as central player, whereas expression of type I interferon (IFN)-β is reduced. Therapeutic treatment of SARS-CoV-infected aged macaques with type I IFN reduces pathology and diminishes pro-inflammatory gene expression, including interleukin-8 (IL-8) levels, without affecting virus replication in the lungs. Thus, ALI in SARS-CoV-infected aged macaques developed as a result of an exacerbated innate host response. The anti-inflammatory action of type I IFN reveals a potential intervention strategy for virus-induced ALI.

Early Upregulation of Acute Respiratory Distress Syndrome-Associated Cytokines Promotes Lethal Disease in an Aged-Mouse Model of Severe Acute Respiratory Syndrome Coronavirus Infection

ABSTRACT Several respiratory viruses, including influenza virus and severe acute respiratory syndrome coronavirus (SARS-CoV), produce more severe disease in the elderly, yet the molecular mechanisms governing age-related susceptibility remain poorly studied. Advanced age was significantly associated with increased SARS-related deaths, primarily due to the onset of early- and late-stage acute respiratory distress syndrome (ARDS) and pulmonary fibrosis. Infection of aged, but not young, mice with recombinant viruses bearing spike glycoproteins derived from early human or palm civet isolates resulted in death accompanied by pathological changes associated with ARDS. In aged mice, a greater number of differentially expressed genes were observed than in young mice, whose responses were significantly delayed. Differences between lethal and nonlethal virus phenotypes in aged mice could be attributed to differences in host response kinetics rather than virus kinetics. SARS-CoV infection induced a range of interferon, cytokine, and pulmonary wound-healing genes, as well as several genes associated with the onset of ARDS. Mice that died also showed unique transcriptional profiles of immune response, apoptosis, cell cycle control, and stress. Cytokines associated with ARDS were significantly upregulated in animals experiencing lung pathology and lethal disease, while the same animals experienced downregulation of the ACE2 receptor. These data suggest that the magnitude and kinetics of a disproportionately strong host innate immune response contributed to severe respiratory stress and lethality. Although the molecular mechanisms governing ARDS pathophysiology remain unknown in aged animals, these studies reveal a strategy for dissecting the genetic pathways by which SARS-CoV infection induces changes in the host response, leading to death.