Statutory and Exotic Viral Diseases
Trevor Drew Statutory and Exotic Viral Diseases Programme Manager
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. Underpinning these aims are extensive research and surveillance activities to support Defra and to link to wider issues associated with our role as an International Reference Laboratory.
Avian influenza testing at VLA Weybridge
Avian Influenza
The unprecedented global spread of H5N1 highly pathogenic avian influenza (HPAI) has resulted in VLA providing national and international support to the UK Government, FAO, OIE, WHO and EFSA (European Food Safety Authority). This support has encompassed our strategic research programme, that has focused on molecular epidemiology, virus pathogenesis, transmissibility, study of physical properties amongst influenza A viruses and population modelling. Advice on the epidemiology and risk assessment of H5 has been utilised by public health bodies developing human vaccine strategies and also provided information on the spread and sources of infection.
VLA senior virologist interviewed as part of the media interest in avian influenza
Molecular epidemiology of the H5N1 influenza viruses in avian populations in Europe, revealed that the virus continues to evolve and many sub-groupings, associated with infection in wild bird populations and poultry, were identified. The viruses undergo very little change whilst they are maintained exclusively in the wild bird reservoir, it is only when they move into poultry that appreciable differences in the virus are detected.
Infection dynamics of HPAI viruses in poultry indicates that the current H5N1 viruses have lower lethal and minimum infectious doses than recent HPAI viruses of the H7 subtype. The lethal dose was up to ten fold lower for chickens and turkeys.
Female mallard (Anas platyrhynchos)
The development and robust validation of new generation tests, with suitability for automation, has greatly contributed to early detection and diagnosis of notifiable avian influenza. This has enabled rapid application of control measures and helped prevent the spread of infection. This approach has been used in response to two AI incidents in the UK and provided extensive support to outbreaks in the EU and other countries. The data now forms part of an EU diagnostic manual for avian influenza.
VLA led an EU epidemiological working group that carried out a complete data analysis on the 2006 EU wild bird surveillance programme. The data confirmed the value of surveillance in dead wild migratory aquatic birds as an early indicator of the incursion of H5N1 HPAI into a region.
Newcastle Disease
During the year, Pigeon Paramyxovirus type-1 (PPMV1) was confirmed in a gamebird holding in Scotland. The virus caused mild infection in grey partridges (Perdix perdix) but the spread was very limited. The virus grouped genetically with other PPMV1s recently isolated in both the UK and Europe and was almost certainly derived from an infected pigeon loft above where the partridges were housed. This work has provided further evidence that game birds may play a significant role in the spread of ND.
As the International Reference Laboratory, we continue to receive viruses from multiple lineages associated with disease in poultry, particularly from Southern and Eastern Europe and from Africa highlighting the continued threat posed by this virus.
Kudu
(Tragelaphus strepsiceros)
Rabies and Wildlife Zoonoses
VLA has continued to act as the UK National Reference Laboratory for rabies and provided a global role to the World Health Organisation as a Communicable Disease Surveillance and Response Collaborating Centre.
In 2006, we were granted OIE status as a Reference Laboratory for rabies and 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. A molecular epidemiological study to investigate rabies epizootics in Kudu (Tragelaphus strepsiceros) was undertaken in collaboration with scientists at the Central Veterinary Laboratory in Windhoek, Namibia and at the University of Pretoria in South Africa. The epidemiological cycles of rabies virus circulating throughout the countries of southern Africa are complex, with a large number of vector species and the existence of at least two distinct biotypes of rabies virus, mongoose and canid. Different species appear to maintain their own cycles of infection eg. non-bite transmission as seen in the Kudu during the epizootics. The canid biotype is now highly established throughout southern Africa, which makes any control programme difficult to implement, due to the large variation in species and habitat.
VLA with the University of Liverpool UK and Blantyre, Malawi looked at a cohort of Malawian children with viral encephalitis. Three of the twenty-six children, originally clinically-diagnosed with cerebral malaria, were later confirmed as having rabies. This report demonstrated that rabies can be underreported in some countries.
Rabies in Bats
The finding of European bat lyssavirus type 2 (EBLV-2) in bats in Great Britain and the death of a bat worker from EBLV- 2 infection highlighted the significance of these viruses. In 2003, targeted surveillance for EBLVs was initiated throughout England and focused on two species of bat, Myotis daubentonii and Eptesicus serotinus. Blood samples were collected and of the 273 E.serotinus samples, the EBLV-2 neutralising antibody prevalence estimate was 1.0 - 4.1% and of the 363 M.daubentonii samples tested the EBLV-1 neutralising antibody prevalence was 0.001 - 1.6%. Oropharyngeal swabs were also collected and host RNA was found in saliva from 83% of the 733 swabs analysed. No cases of live lyssavirus infection or lyssavirus viral RNA were detected.
In September 2006, a bat variant of rabies virus EBLV-2 was isolated from a Daubenton’s bat found in Oxfordshire. This case represents the fifth isolation of EBLV-2 from a Daubenton’s bat in Great Britain.
West Nile Virus
Between 2001-2006, a total of 1,867 birds representing 128 species from all geographical areas of England, Wales and Scotland have been examined, but no evidence of West Nile Virus (WNV) infection has been detected. Surveillance for neurological disease in horses, including WNV and other emerging diseases such as Borna and Hendra viruses, is on-going. WNV infection, which is now notifiable in horses, has never been detected in animals that have exhibited neurological signs in the UK.
Classical Swine Fever (CSF)
CSF represents a major threat to the UK pig industry and as a National and OIE Reference Laboratory for the disease, surveillance and directed diagnostic testing is carried out to ensure rapid and efficient detection. We have participated in ring trials organised by the EU Community Reference Laboratory and have collaborated with the Onderstepoort Veterinary Institute, RSA, on the susceptibility of wildlife Suidae to CSF. Research projects focusing on the mechanisms by which the virus is able to suppress the natural immune reaction and the evaluation of strategies for vaccination and therapeutic approaches are in progress.
Viral Diseases of Other Species
As an OIE Reference Laboratory for Enzootic Bovine Leukosis (EBL), VLA is working to improve diagnostic tests and to ensure that newly emerging strains can be detected. Equine Infectious Anaemia (EIA) is another retrovirus disease, which previously had not occurred in the UK or Ireland for almost 30 years. In 2006, an outbreak was detected in Ireland and several horses had to be quarantined in the UK. VLA provided all of the testing associated with the clearance of horses under quarantine. VLA scientists have also been trained in Bluetongue diagnosis at IAH, as a contingency for possible outbreaks in the UK.