Statutory and Exotic Viral Diseases
Avian influenza virus
The aim of the Statutory and Exotic Viral Diseases Programme is to provide Defra and other institutes and agencies with an early warning system and an expert consultancy and diagnostic service for statutory and exotic virus diseases of animals, including those that may affect human health. Underpinning these aims are extensive surveillance and research activities to support Defra and also link to wider issues, associated with our role as an International Reference Laboratory for a number of viral diseases.
Rabies and Wildlife Zoonoses
Programme Manager
VLA is the UK National Reference Laboratory for rabies also providing a global role to the World Health Organisation as a Communicable Disease Surveillance and Response Collaborating Centre for the characterisation of rabies and rabiesrelated viruses. These activities have led to numerous international collaborations to further understand the holistic nature of rabies and to prevent incursions of the virus into the UK.
Global epidemiology of classical rabies virus
Our collection of rabies virus isolates from different countries has been further expanded by the acquisition of from wildlife, from domestic animals and from two human cases. Arctic regions including Greenland, Canada and Alaska has provided evidence of the movement of rabies across borders. Rabies is an increasing problem in China and working with the Chinese Academy of Sciences in Beijing, we reported the number of dog-mediated rabies cases and how this has led to a concomitant high human mortality, affecting people principally living in poor, rural communities.
Human cases of rabies imported to the UK
A human case of rabies was diagnosed in a female patient returning from a holiday in Goa, India. It represented a case of fatal ‘paralytic’ rabies, acquired in a rabiesendemic country following a dog bite in the absence of pre- or post-exposure prophylaxis against rabies.
(Myotis daubentonii)
Rabies in bats
Targeted surveillance of rabies in bats has been increased and although an antibody prevalence level of 3 - 8% of European Bat Lyssavirus (EBLV-2) in M.daubentonii and one bat with antibodies to EBLV-1 in E.serotinus was detected, no cases of live lyssavirus infection or lyssavirus viral RNA have been detected.
Surveillance of West Nile Virus in birds
Surveillance has also been carried out on avian species, mainly corvids and passerines, for the presence of viral RNA to West Nile Fever Virus. Using validated PCR methods there were no reported positive WNV cases in birds tested in 2005.
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Mammalian Virology
Classical Swine Fever Virus (CSFV)
CSFV is still a major threat to the UK pig industry, as demonstrated by the recent outbreak in Germany and the extension of the outbreaks in the new EU accession member states. As an OIE Reference Laboratory, we carry out confirmatory diagnostic testing for many countries (including most recently South Africa) and have participated in ring trials organised by the EU Community Reference Lab (CRL). A CSF specific, real time PCR has been developed and evaluated and is now included in our portfolio of UKAS ISO 17025 accredited tests.
In collaboration with IAH, we have further elucidated the role viral proteins play in suppressing the most immediate, innate immune reaction. Further studies were implemented to identify opportunities to silence the virus during infection by small interfering RiboNucleic Acid (siRNA) and to analyse the safety of vaccination.
Other exotic viral diseases of pigs
VLA acts as an EU recognised national laboratory for both Aujeszky’s disease and porcine encephalomyelitis. We also monitor for the American strain of PRRS. Currently, the UK is free of these diseases but many European and other countries are not.
Viral diseases of other species
Whilst the UK is free of Enzootic Bovine Leukosis (EBL) and Equine Viral Arteritis (EVA) they are still widely present throughout the EU. As an OIE Reference Laboratory, VLA is working to improve molecular tests and to ensure that any newly emerging strains can be detected.
Avian Virology
Avian Influenza
During 2005, VLA as the OIE, FAO and EU community reference laboratory (CRL) received 387 isolates for identification and confirmatory diagnosis and 128 were influenza A viruses. An increased proportion of H5N1 viruses reflected the continued global spread including the first incursions into Europe. We have increasingly been involved in the investigation of many associated outbreaks through the provision of confirmatory diagnosis and direct support by a variety of means to infected ‘third’ countries.
The majority of reports of H5N1 involved the detection or isolation of virus from wild birds that had been found dead. Molecular epidemiology, based on sequence analyses of the haemagglutinin gene revealed high homogeneity amongst all these viruses which were also very closely related to the viruses present in eastern and central Asia. One mechanism of virus spread to Europe was by migratory wild birds that were found positive in many countries with no associated outbreaks in poultry, providing the first definitive evidence for the involvement of wild birds in the epidemiology of highly pathogenic avian influenza (HPAI). Further infection of wild birds through exposure to infected ‘backyard’ poultry in eastern Europe appears probable. In our role as the CRL, we have provided advice, guidance and direction in developing these evolving programmes, that have been modified to obtain greater focus based on risk for the detection of H5 or H7 positive domestic and wild birds. Through our statutory functions as a national reference laboratory for AI we diagnosed the first recorded instance of H5N1 HPAI virus in a consignment of birds from Asia held in a UK quarantine station, which highlighted the risk of introduction through the trade in captive birds. The virus found, although distinct, was closely related to other H5N1 viruses identified in Europe.
The preliminary results of a collaborative project, with several institutes and funded by BBSRC, into the infection dynamics of HPAI viruses, indicated that a lower infectious dose of virus is required to infect turkeys compared to chickens. Furthermore, although the trajectory of virus shedding appears similar between both species, it is elevated approximately ten-fold in turkeys. Some marked variability between individual chickens in terms of the virus shedding profile was detected, indicating that some birds may be more influential for virus transmission within a flock.
A European ring trial coordinated by VLA, provided critical data for supporting the development of a testing strategy that included the use of molecular diagnostics. Significant progress has been made in the development, validation and application of real-time RT-PCRs using clinical specimens and two assays, based on the detection of influenza A viruses and H5 specific viruses have been adapted for routine screening. A lateral flow device has also been looked at for possible on-farm use.
A novel protocol has been developed to enable the rescue of avian viruses, generated by reverse genetics within embryonated fowl eggs to study the individual mutations in viral genes for their influence on virulence, host range and transmissibility.
Newcastle Disease Virus (NDV)
As the OIE, FAO and EU reference laboratory, VLA received 179 isolates of avian paramyxoviruses for identification and confirmatory diagnosis. During 2005, the first UK outbreak of NDv since 1997 was reported on a pheasant farm in Surrey. The affected premises was depopulated, cleansed and disinfected and there was no reported spread of the disease. The source of the outbreak was most probably through a consignment of pheasants imported from France.
The infection spread relatively slowly through the farm and induced generally mild clinical symptoms. The virus was characterised as gene lineage 5b and was closely related to other viruses isolated from NDv outbreaks in poultry in Europe during the last year. This lineage had been reported from the Far East and an isolated case in the Middle East.
The identification of genetic markers for virulence form part of our statutory testing to characterise the pathogenicity of virus and a new system has been designed using the application of real time RT-PCR technology for pathotyping NDV isolates. Preliminary results using over 100 virus isolates with broad heterogeneity have been tested and high correlation with gold standard invivo tests has been achieved.
Avian meta pneumovirus (aMPV) and infectious bronchitis virus (IBV)
A real-time RT-PCR has been developed for the detection of aMPV and avian coronavirus including IBV, which can detect and discriminate between aMPV subtypes A, B and C. In addition, a further test was designed to detect a broad range of avian coronaviruses and was successfully applied to a range reference strains.
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| Rabies and Wildlife Zoonoses |
| Mammalian Virology |
| Avian Virology |