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Pathogenesis and the immune response to influenza in farmed anseriformes - SE0782

Description
Wild aquatic birds provide the primary reservoir for all avian influenza (AI) viruses and have been implicated in the spread of influenza to domestic poultry, with some strains causing outbreaks of highly pathogenic avian influenza (HPAI). In recent years there have also been transmissions of AI viruses to humans raising concerns over the potential for the emergence of pandemic strains. For these reasons Defra and the European Community have recognised that it is important to assess influenza virus circulation in aquatic birds through virological and serological surveillance studies.

However, at present there is only limited information in the scientific literature about the serological response of ducks or other waterfowl following infection with HPAI viruses and there are no validated diagnostic tests (sensitivity and specificity values are not available). Such technical gaps should be filled as quickly as possible to improve the efficiency of surveillance measures.

Ducks can be infected with HPAI viruses without showing signs of disease. This may be of great concern because these viruses could become widespread in the host population without raising alarm and thus present a risk of transmission to other classes of poultry that have greater economic significance e.g. chickens and turkeys.

Studies by Alexander et al [1 and 2] compared the pathogenicity of HPAI and LPAI H5 and H7 avian influenza viruses for ducks, chickens, turkeys and quail when inoculated by various routes including intramuscula, intranasal and to in contact birds. These studies demonstrated the refractory nature of ducks for HPAI and also highlighted the ability of such birds to be infected an excreting virues which are extremely pathogenic for galliform birds. However, viral load in the tissues was not measured and serological investigations were limited to haemagglutination inhibition tests on sera collected twenty one days post infection. The virus load in the tissues of ducks infected by one of five avian influenza viruses was determined over a time-course by Wood et al. [3], but no molecular techniques were employed and no serology was done.

Viruses of the ‘Asian’ H5N1 lineages are reported to have resulted in mortalities for wild waterfowl domestic duck flocks and wild migratory birds. Several studies have examined the replication of viruses from these lineages in ducks [4-6]. However, these studies have not made comparisons with viruses from the Eurasian lineage.

The purpose of this project is to determine, the trajectory of virus shedding, immunological responses and routes/rates of transmission for different strains of HPAI virus. Such information will allow an assessment of the risk that AI infection in farmed ducks poses to other sectors of the poultry industry. Control measures can then be devised and implemented in an informed way. To date the lack of immunological data in particular has presented difficulties in developing a validated approach to conducting reliable AI surveillance in ducks EU wide.

Ducks will be infected with HPAI viruses selected to represent all the current Eurasian phylogenetic lineages and also with low pathogenicity avian influenza viruses (LPAI) to give baseline data which will allow comparison with the infection model previously developed for AI infections in chickens and turkeys. The immune response and the evaluation of shedding will be determined over an extended period of time in order to ascertain the role of these birds as silent reservoirs of infection.

Briefly, one group of birds will be challege infected, then placed in contact with a second uninfected group. Buccal and cloacal swabs will be collected daily for determination of virus load by real time RT-PCR. Blood samples will be collected weekly and seroconversion will be measured by haemagglutination inhibition tests (HAI) for H5 or H7 antigen or Blocking ELISA for the nuclear protein (NP). Similar experiments will use vaccinated/previously infected (with LPAI) birds instead of naive birds, to determine the effect of vaccination/previous infection on the transmission parameters. Such experiments will provide data that are required for detailed epidemiological outbreak analyses, will provide an insight into the efficacy of control strategies and thus support the decision making processes of competent authorities.

In addition, pen-side tests for AI antigen detection on farm will be developed. This will be done at CSL in collaboration with VLA and other members of the EU FLUAID project consortium. The objective is to develop a rapid and sensitive test which is able to identify positive flocks and generate information on whether the virus is of the H5 or H7 subtype. The platform will be an immunchromatographic assay in a lateral flow device.

Objective
1. Define laboratory approaches and optimise methodology as required.

2. Investigate the pathogenesis, dynamics of virus shedding and transmission of HPAI (x5) viruses in ducks.

3. Investigate protective antibody levels and the efficacy of vaccination on the transmission of AI in ducks.
Project Documents
• Final Report : Pathogenesis and the immune response to influenza in farmed anseriforms   (1615k)
Time-Scale and Cost
From: 2006

To: 2010

Cost: £355,746
Contractor / Funded Organisations
Veterinary Laboratories Agency
Keywords
Animal Diseases              
Animal Health              
Immunity              
Influenza              
Pathogenesis              
Plants and Animals              
Fields of Study
Animal Health