Uk Phocine Distemper Virus Epizootic
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UK PHOCINE DISTEMPER VIRUS EPIZOOTIC INVESTIGATION REPORT 2002/2003 Final Report Conducted for the Department for Environment, Food and Rural Affairs (Defra) Collaborative investigation co-ordinated by the Institute of Zoology The Zoological Society of London Regent’s Park London NW1 4RY England Compiled by: Becki Lawson MA VetMB MSc MRCVS Paul D. Jepson BVMS PhD MRCVS Contract start date: 13th August 2002 Contract end date: 31st August 2003 Phocine Distemper Virus Epizootic Investigation 2002/2003 Phocine Distemper Virus Epizootic Investigation 2002/2003 2 Contents • Preface 5 • Executive Summary 6 • Introduction 7 • Overview of Morbilliviruses in Marine Mammals 7 • Aim of Investigation 11 • Objectives of the Investigation 11 • Materials and Methods 12 Project Organisation and Response Plan 12 Opportunistic Reporting of Dead Seals 12 Systematic Reporting of Dead Seals 13 Data Recording 15 Pathological Investigations 16 Serological Investigations (Feline herpesvirus/Toxoplasma) 19 Carcass Disposal 20 Information Distribution 21 Aerial Census Surveys and Population Estimates 22 Quantification of Regional Seal Mortality 23 • Results 24 Monitoring of UK seal mortality 24 Pathological Investigations 27 Patterns of PDV exposure in UK seals 32 Patterns of UK Seal Mortality 36 Quantification of Seal Mortality (Aerial Survey) 40 Comparative epidemiology of 1988 and 2002 PDV epizootics 43 Opportunistic Reporting of Dead Seals (National Seal Hotline) 46 Systematic Reporting of Dead Seals 46 Information Distribution and Media Management 48 • Discussion 51 Epidemiology of the 2002 UK PDV Epizootic 52 Comparison of the 1988 and 2002 PDV Epizootic Epidemiology 53 Pathological Investigations 54 Molecular Diagnostic Testing 56 Opportunistic Reporting 56 Systematic Reporting 57 Carcass Disposal 58 • Recommendations for the Investigation of Future Wildlife Epizootics 60 • Investigation Outputs 62 • Parallel Research 62 • Future Research 62 • Cited References/Bibliography 64 • Appendices 1. Organisation Contact Directory 1.1 Collaborators and Participating Organisations 1.2 Other Related Organisations 1.3 English Local Authority Details 2. Defra Website Information Phocine Distemper Virus Epizootic Investigation 2002/2003 3 2.1 Defra News Release 2.2 Seals and Phocine Distemper Virus (PDV) 2.3 Suggested Disposal Options for Seal Carcasses 2.4 Do you own land on the coast? Letter providing guidelines to private landowners along the coast 2.5 Frequently asked questions about Phocine Distemper Virus 2.6 Options for a vaccination program 2.8 Public health guidance note issued by the Scottish Centre for Inspection and Environmental Health 3. Volunteer Guidelines 4. Post mortem examination protocol and report pro forma 5. Media and Information Dissemination 5.1 Zoology Society of London Press Release 5.2 - 5.3 Zoological Society of London Interview and Coverage Log 5.4 Greenland Interactive National Seal Hotline Call Log 5.5 Example of UK PDV Status Report 6. Images 7. Systematic Reporting - Volunteer Appeal Appraisal Phocine Distemper Virus Epizootic Investigation 2002/2003 4 • Preface Following the re-emergence of phocine distemper virus (PDV) in European common seals (Phoca vitulina) in May 2002, it was evident that a pan-European outbreak of the same viral disease that killed approximately 18,000 seals in 1988 was likely to re-occur. The devastating consequences of the 1988 epizootic resulted in one of the largest and most high profile epizootics affecting indigenous wildlife species in the UK. In August 2002 the UK Government (Defra) elected to fund a large-scale national collaborative research project. The principal aims of the investigation were to investigate the impact of the 2002 PDV epizootic on UK seal populations, advise Government on the most appropriate response to the disease outbreak, and to rapidly disseminate information to all interested parties including the general public. Organisation of the investigation involved liaison between governmental bodies, research and academic institutions, local authorities, animal rescue charities, non-governmental organisations, commercial groups and members of the public. The co-ordination of this multidisciplinary project relied on close and continual collaboration between all parties. A preliminary report, submitted to Defra in September 2003, gave particular emphasis to the methodology and management of the investigation coupled with an appraisal of its successes and limitations to date. Information on lessons learnt will be of use for investigation of future disease outbreaks affecting marine mammals and other free-ranging wildlife species. This final version of this report also incorporates a review of morbilliviruses in marine mammals, the full suite of diagnostic and histopathological test results from the investigation, and population estimates derived from aerial census surveys enabling the most accurate predictions of the impact of the 2002 PDV epizootic on UK common and grey seal (Halichoerus grypus) populations. Phocine Distemper Virus Epizootic Investigation 2002/2003 5 • Executive Summary Approximately 18,000 common seals (Phoca vitulina) and 500 grey seals (Halichoerus grypus) died during the 1988 European phocine distemper virus (PDV) epizootic. Most seal populations subsequently recovered to pre-epizootic levels. In May 2002 a second European PDV epizootic began on Anholt Island in the Kattegat, the same location where the 1988 epizootic was initiated. In August 2002, following the spread of the epizootic into the North Sea and Waddensea, the UK Government funded a national collaborative research project to investigate the impact of the PDV epizootic on UK seal populations. Shortly afterwards the first case of PDV infection in the UK was confirmed in a common seal, examined by RSPCA veterinarians, that had been found in The Wash in July 2002. Reports of dead seals were obtained opportunistically through a National Seal Hotline telephone number, from Local Authorities and via a network of volunteers systematically monitoring stretches of UK coastline. This enabled the identification of spatial and temporal trends in seal mortality. The National Seal Hotline also forwarded any reports of sick live seals to the RSPCA and Scottish SPCA. Seal carcasses were retrieved or examined in situ using standardised necropsy techniques to monitor the spread of the virus and to facilitate the archiving of tissue samples for research purposes. PDV infection was confirmed by specialist laboratories using reverse-transcriptase polymerase chain reaction (RT-PCR) and/or immunohistochemistry. Weekly Status Reports were collated and posted on the Sea Mammal Research Unit (SMRU) website, and a recorded message was hosted on the National Seal Hotline, enabling the latest information on seal strandings and post mortem investigation results to be rapidly placed within the public domain. Epizootic common seal mortality increased rapidly within The Wash to reach a peak in mid-September followed by a gradual decline to background levels of mortality by November/December 2002. Molecular testing confirmed PDV infection in 69/77 (90%) of common seals examined from The Wash between July and October inclusive, most of which had gross and microscopic lesions consistent with fatal phocine distemper. Pre and post-epizootic aerial surveys indicated that 13-18% of The Wash common seal population died; significantly lower than during the 1988 PDV epizootic. Based on carcass counts and aerial survey data there was no perceptible increase in common or grey seal mortality in Scotland, Wales or Northern Ireland. PDV infection was confirmed in 12/27 (44%) of common and 9/42 (21%) of grey seals in Scotland examined between September 2002 and January 2003, but only 6 common seals from Scotland were diagnosed to have died due to phocine distemper. Two cases of PDV infection were confirmed in seals from Northern Ireland but no cases were reported from colonies in Wales, Shetland or Cornwall. No cases of fatal distemper were diagnosed in any UK grey seals. Concerns that PDV could over- winter in UK seals and induce subsequent epizootic-type mortality in Scottish common seals in the summer of 2003 during periods of high seal haul-out density proved unfounded. Reasons for the lower common seal mortality rates in Scotland are incompletely understood, although epidemiological factors such as lower seal haul-out densities during periods of viral exposure, lower pollutant levels, and increased genetic resistance due to historical PDV exposure have been suggested. Epidemiological modelling incorporating movement probabilities between colonies may assist in addressing these uncertainties and in predicting the frequencies and impacts of future PDV epizootics on European seal populations. Phocine Distemper Virus Epizootic Investigation 2002/2003 6 • Introduction During 1988 a major epizootic of phocine distemper caused the death of approximately 18,000 common, or harbour, seals (Phoca vitulina) and 500 grey seals (Halichoerus grypus) in European waters. The epizootic, caused by phocine distemper virus (PDV), began in the Kattegat and spread over several months to infect seals in the Baltic, Waddensea, North Sea and Irish Sea. Considerable scientific research was conducted in 1988-1989 in the UK and in other parts of Europe to initially identify the cause of the 1988 die-off and to assess the epidemiological impact of the PDV epizootic on UK and European seals. Within the UK, the greatest declines in common seal populations occurred