Avian Influenza: Impact of Virus-host Interactions on Pathogenesis and Ecology
Highly pathogenic avian influenza viruses (HPAIV) have acquired the unprecedented and alarming capacity to infect humans. By establishing a permanent ecological niche in wild birds, HPAIV will pose a continuous risk for poultry and fatal human infections, especially if these birds excrete HPAIV without showing any clinical signs of disease. These changes in the ecology of the disease and behaviour of the virus may create opportunities for a pandemic virus to emerge.
Attempts to avoid or contain HPAIV outbreaks have been largely unsuccessful. This can be directly linked to our lack of fundamental knowledge. Therefore, it is essential to increase our knowledge of the ecology and pathology of avian influenza virus infections in poultry and other species.
Full understanding of the ecology and pathogenesis of HPAIV requires a multi-disciplinary approach determining host-pathogen interactions and the role played by the host immune response. To this end, the FLUPATH consortium was established.
FLUPATH is composed of 13 partners, six of which are National Reference Laboratories for avian influenza. The consortium further includes five academic institutions and two institutions that specialise in animal science and health. The participants, with expertise in chicken genomics, micro array technology, pathology, receptors, innate immunity and chicken immunology will use multidisciplinary and complementary approaches to address key problems and unanswered questions with respect to the ecology and pathogenesis of avian influenza.
FLUPATH will provide knowledge and tools for new strategies which will be tailored for the control and management of avian influenza at the European and international level. This will limit the impact of the disease both in terms of human health and losses to the poultry industry. The accompanying reduction in animal slaughter and financial and economic losses will place a significantly lower demand on EU and Member States' budgets.[+] Read More
Lack of sufficient fundamental knowledge: avian influenza represents one of the major concerns for public health that has recently emerged from the animal reservoir. The increased relevance of avian influenza in the fields of animal and human health has highlighted the lack of scientific information on the disease. This has hampered the management of some of the recent crises, resulting in millions of dead animals, concern over loss of human lives and management of the virus's pandemic potential. For this reason, and for the devastating effects on the poultry industry, international organisations such as WHO, OIE and FAO have worked together and established a coordinated set of guidelines and action plans to combat the ongoing Asian epidemic.
Due to the low profile of avian influenza until 1997, a significant amount of information and the specific tools necessary to manage avian influenza epidemics adequately are lacking. This includes both the EU situation and the ongoing H5N1 crisis. Recent outbreaks of HPAI have affected avian species that are showing a reduced susceptibility to this virus. If HPAI infection of the wild bird host becomes compatible with normal behavioural patterns and migration, the result will be the development of an endemic cycle in wild birds. The consequences of such a situation are unpredictable and potentially very dangerous.
Retrospective analysis of recent outbreaks has permitted the identification of weak points in the management system that represent areas of uncertainty for which improvement is required. Several of these weak points can be directly linked to our lack of fundamental knowledge about the importance of both viral as well as host factors in determining the outcome of infection. Therefore, it is essential to increase our effort to enhance our knowledge about the ecology and pathology of avian influenza virus infections in poultry and other species.
This proposal aims to generate data on significant issues linked to AI outbreak management on which scientific knowledge is currently lacking. These issues are all related to virus-host interactions. Four major tasks (work packages) have been identified which address the objectives of task 3 of the EU call SSP5-B INFLUENZA: ecology and pathogenesis of avian influenza infections:
Work Package 1 (WP1) addresses the issue of pathogen-host interactions and virulence determinants at the molecular level. Little is know about the host-response following infection with viruses that differ in virulence and gene constellation. The contribution of specific viral genes - or gene sequences - to pathogenesis, host- and tissue-tropism as well as their role in interference with host defence mechanisms will be examined in vivo in different species in animal experiments as well as in vitro using professional antigen presenting cells such as dendritic cells and macrophages (see also WP4 below). State-of-the-art technology such as gene-expression profiling using DNA micro-arrays and identification of differentially expressed genes using gene libraries obtained by suppression subtractive hybridisation (SSH), will be used to identify specific host genes which are involved in the reaction to infection by specific avian influenza virus genotypes. The involvement and importance of viral genes as well as host genes will be evaluated by cross-validation and in vitro experiments.
Work Package 2 (WP2) is mainly concerned with studying the ecology and pathology of different avian influenza strains in different host species. These studies will evaluate and compare host-pathogen interactions of different HPAI and LPAI viruses. These evaluations include histopathological descriptions of virus infection, quantification of viral loads in different organs and tissues by real-time RT-PCR and confocal immunohistochemistry. Apart from chickens, specific attention will be given to water birds such as ducks (mallard) which seem to be clinically less susceptible to highly pathogenic avian influenza and therefore are implicated in transmission of the virus. Furthermore, experiments on pigs will be conducted in order to assess their role in maintenance and transmission of avian influenza since pigs may serve as a 'mixing vessel' for avian and human viruses. The significance of several adaptive mutations such as the NS1 truncations and lys 627 PB2 mutations will be examined in a chicken and mouse model system using either natural isolates or specific mutants generated by means of reverse genetics. Finally, the capacity of avian influenza to cross the species barrier will be examined by using mammalian-adapted viruses.
Work Package 3 (WP3) will address the issue of virus-receptor interactions with the goal of determining the role of receptor specificity and neuraminidase activity of avian viruses in interspecies transmission, pathogenicity and emergence of potentially new pandemic strains. Different receptor phenotypes might provide the virus with an enhanced potential for interspecies transmission to pigs and humans. Molecular mechanisms for avian-to-avian, avian-to-pig and avian-to-human transmission will be studied by using different cells and tissues including tracheal explants from chickens, turkeys and ducks, and cultures of human airway epithelium.
Work Package 4 (WP4) is concerned with the identification of virulence factors that determine avian influenza virus pathogenesis and transmissibility, focusing on the interaction of HPAI and LPAI viruses with the innate immune system. These studies will analyse the requirements of the virus to adapt to its host and to interact with the different cellular compartments of the innate defence system, in particular dendritic cells (DC), macrophages (MF) and natural killer (NK) cells. The role of the HA protein in eliciting in vivo and in vitro cytokine responses will also be investigated.
The FLUPATH proposal will improve our understanding of the origins of HPAIV, the patterns of its evolution, and its behaviour in avian and mammalian species. Work on currently circulating viruses will allow us to track changes in the present situation and thus issue precise warnings, should the threat of a pandemic increase.
It is anticipated that this approach will permit a more complete understanding of the immunological, cell biological and molecular basis of the threat posed by HPAIV such as the current H5N1. Essential information on critical viral and host factors, which determine the transmissibility of the virus to mammals, will be determined. This knowledge will clearly be of high value when implemented in novel strategies to combat avian influenza.
FLUPATH will ultimately provide knowledge and tools for new strategies which will be tailored for the control and management of AI at both a European and international level. This should result in a noticeable reduction in the impact that this disease has had in the past.