Ecology, Evolution and Pathogenesis of Avian Influenza Viruses

Influenza A virus behoort tot de familie van Orthomyxoviridae. Infl uenza A virussen zijn onregelmatig gevormde virussen van ongeveer 120 nm groot. Het genoom van influenza A virussen is gesegmenteerd en bestaat uit negatief-strengs RNA. De acht gensegmenten coderen voor 11 verschillende eiwitten. Infl uenza A virussen worden onderverdeeld op basis van de oppervlakte eiwitten; hemagglutinine (HA, een eiwit dat zorg draagt voor de binding van het virus aan en binnendringen van de gastheercel) en neuraminidase (NA, een eiwit dat zorgt voor de efficiënte verspreiding na vermenigvuldiging van het virus). Er waren tot voor kort 15 verschillende subtypen van HA geïdentificeerd en 9 verschillende subtypen van NA. Dit leidt tot 135 potentiële subtype combinaties zoals H1N1, H3N2, H5N1 en H7N7. Aviaire influenza virussen zijn verder in te delen op grond van biologische eigenschappen: laag pathogene aviaire influenza virussen (LPAI), die geen tot milde ziekteverschijnselen veroorzaken en hoog pathogene aviare influenza virussen (HPAI), die massale sterfte onder pluimvee kunnen veroorzaken (ook bekend als vogelpest). Influenza A virus is voornamelijk bekend als veroorzaker van de drie pandemieën (wereldwijde uitbraken) van de afgelopen eeuw: de H1N1 Spaanse griep in 1918, de H2N2 Aziatische griep in 1957 en de H3N2 Hong Kong griep in 1968. Daarnaast is het ook bekend van de jaarlijks terugkerende griepepidemieën (lokale uitbraken) en van uitbraken van vogelpest. Hoewel het bekend is dat alle infl uenza A virussen hun oorsprong hebben in wilde vogels, is er weinig bekend over het voorkomen van aviaire influenza virussen in wilde vogels in Europa. Het onderzoek beschreven in dit proefschrift richtte zich in eerste instantie op het in kaart brengen van de complexe ecologie van aviaire influenza virussen in hun natuurlijke gastheer, de wilde vogels, en vervolgens op de veranderingen die ten grondslag liggen aan het vermogen van deze virussen om overgedragen te kunnen worden naar de mens. Hoofdstuk 1 geeft een algemene inleiding en een overzicht van de huidige kennis over het voorkomen van infl uenza A virussen in wilde vogels. Hierbij wordt ingegaan op de rol die verschillende vogelfamilies spelen in de ecologie van infl uenza A virussen zoals de Anseriformes (eenden, ganzen en zwanen) en Charadriformes (meeuwen, alken en steltlopers)

The molecular basis of the pathogenicity of the Dutch highly pathogenic human influenza A H7N7 viruses

During the highly pathogenic avian influenza (HPAI) H7N7 virus outbreak in The Netherlands in 2003, 88 infected persons suffered from mild illnesses, and 1 died of pneumonia. Here, we studied which of the 14 amino acid substitutions observed between the fatal case (FC) virus and a conjunctivitis case (CC) virus determined the differences in virus pathogenicity. In virus-attachment experiments, the CC and FC viruses revealed marked differences in binding to the lower respiratory tract of humans. In a mouse model, the hemagglutinin (HA) gene of the FC virus was a determinant of virus tissue distribution. The lysine at position 627 of basic polymerase 2 (PB2) of the FC virus was the major determinant of pathogenicity and tissue distribution. Thus, remarkable similarities were revealed between recent HPAI H5N1 and H7N7 viruses. We conclude that the influenza virus HA and PB2 genes should be the prime targets for molecular surveillance during outbreaks of zoonotic HPAI viruses

Avian influenza a virus in wild birds in highly urbanized areas

Avian influenza virus (AIV) surveillance studies in wild birds are usually conducted in rural areas and nature reserves. Less is known of avian influenza virus prevalence in wild birds located in densely populated urban areas, while these birds are more likely to be in close contact with humans. Influenza virus prevalence was investigated in 6059 wild birds sampled in cities in the Netherlands between 2006 and 2009, and compared with parallel AIV surveillance data from low urbanized areas in the Netherlands. Viral prevalence varied with the level of urbanization, with highest prevalence in low urbanized areas. Within cities virus was detected in 0.5% of birds, while seroprevalence exceeded 50%. Ring recoveries of urban wild birds sampled for virus detection demonstrated that most birds were sighted within the same city, while few were sighted in other cities or migrated up to 2659 km away from the sample location in the Netherlands. Here we show that urban birds were infected with AIVs and that urban birds were not separated completely from populations of long-distance migrants. The latter suggests that wild birds in cities may play a role in the introduction of AIVs into cities. Thus, urban bird populations should not be excluded as a human-animal interface for influenza viruses

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) Does Not Replicate in Syrian Hamsters

In 2012 a novel coronavirus, MERS-CoV, associated with severe respiratory disease emerged in the Arabian Peninsula. To date, 55 human cases have been reported, including 31 fatal cases. Several of the cases were likely a result of human-to-human transmission. The emergence of this novel coronavirus prompts the need for a small animal model to study the pathogenesis of this virus and to test the efficacy of potential intervention strategies. In this study we explored the use of Syrian hamsters as a small animal disease model, using intratracheal inoculation and inoculation via aerosol. Clinical signs of disease, virus replication, histological lesions, cytokine upregulation nor seroconversion were observed in any of the inoculated animals, indicating that MERS-CoV does not replicate in Syrian hamsters

Heterosubtypic Immunity to Influenza A Virus Infections in Mallards May Explain Existence of Multiple Virus Subtypes

Wild birds, particularly duck species, are the main reservoir of influenza A virus (IAV) in nature. However, knowledge of IAV infection dynamics in the wild bird reservoir, and the development of immune responses, are essentially absent. Importantly, a detailed understanding of how subtype diversity is generated and maintained is lacking. To address this, 18,679 samples from 7728 Mallard ducks captured between 2002 and 2009 at a single stopover site in Sweden were screened for IAV infections, and the resulting 1081 virus isolates were analyzed for patterns of immunity. We found support for development of homosubtypic hemagglutinin (HA) immunity during the peak of IAV infections in the fall. Moreover, re-infections with the same HA subtype and related prevalent HA subtypes were uncommon, suggesting the development of natural homosubtypic and heterosubtypic immunity (p-value = 0.02). Heterosubtypic immunity followed phylogenetic relatedness of HA subtypes, both at the level of HA clades (p-value = 0.04) and the level of HA groups (p-value = 0.05). In contrast, infection patterns did not support specific immunity for neuraminidase (NA) subtypes. For the H1 and H3 Clades, heterosubtypic immunity showed a clear temporal pattern and we estimated within-clade immunity to last at least 30 days. The strength and duration of heterosubtypic immunity has important implications for tran

Characterization of a novel influenza A virus hemagglutinin subtype (H16) obtained from black-headed gulls.

In wild aquatic birds and poultry around the world, influenza A viruses carrying 15 antigenic subtypes of hemagglutinin (HA) and 9 antigenic subtypes of neuraminidase (NA) have been described. Here we describe a previously unidentified antigenic subtype of HA (H16), detected in viruses circulating in black-headed gulls in Sweden. In agreement with established criteria for the definition of antigenic subtypes, hemagglutination inhibition assays and immunodiffusion assays failed to detect specific reactivity between H16 and the previously described subtypes H1 to H15. Genetically, H16 HA was found to be distantly related to H13 HA, a subtype also detected exclusively in shorebirds, and the amino acid composition of the putative receptor-binding site of H13 and H16 HAs was found to be distinct from that in HA subtypes circulating in ducks and geese. The H16 viruses contained NA genes that were similar to those of other Eurasian shorebirds but genetically distinct from N3 genes detected in other birds and geographical locations. The European gull viruses were further distinguishable fro

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

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

Airborne transmission of influenza A/H5N1 virus between ferrets

Highly pathogenic avian influenza A/H5N1 virus can cause morbidity and mortality in humans but thus far has not acquired the ability to be transmitted by aerosol or respiratory droplet ("airborne transmission") between humans. To address the concern that the virus could acquire this ability under natural conditions, we genetically modified A/H5N1 virus by site-directed mutagenesis and subsequent serial passage in ferrets. The genetically modified A/H5N1 virus acquired mutations during passage in ferrets, ultimately becoming airborne transmissible in ferrets. None of the recipient ferrets died after airborne infection with the mutant A/H5N1 viruses. Four amino acid substitutions in the host receptor-binding protein hemagglutinin, and one in the polymerase complex protein basic polymerase 2, were consistently present in airborne-transmitted viruses. The transmissible viruses were sensitive to the antiviral drug oseltamivir and reacted well with antisera raised against H5 influenza vaccine strains. Thus, avian A/H5N1 influenza viruses can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host and therefore constitute a risk for human pandemic influenza