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Porcine reproductive and respiratory syndrome virus: emergence of novel strains in Britain - SE0525

This research aims to identify novel strains of PRRSV associated with disease in pigs in Britain, with special emphasis placed on those associated with severe respiratory disease and/or high numbers of stillbirths and neonatal deaths. The emerging information on the evolution of PRRS in continental Europe is a disturbing one – there are reports of more severe disease and emergence of strains which are significantly different from those described from the early 1990s. In Britain, there are likewise reports of anomalies in serological testing, suggesting diversity and significant evolution (M. Donadeu, PIC, personal communication). Between 1991 and 1995, a MAFF-funded project revealed the extraordinary rapidity with which the UK strain was evolving (Drew et al 1997) but no studies have been carried out since that time. This project therefore aims to examine current strains, with a view to determining their diversity and to find out whether any new strains have been introduced from Europe or the US. The project also aims to refine tests currently used for serodiagnosis of disease, in the light of findings within this project.The knowledge that will emerge from this study will inform Defra and the pig industry of the strains of PRRSV currently in Britain and will aid clinicians and decision-makers concerning the potential efficacy of vaccines and will also allow refinements to enable more accurate diagnosis. Furthermore, evidence provided from this project will provide valuable data for risk assessments, allowing informed decision-making by Defra concerning the future policy on importation of meat and livestock from Accession States of the EU.The primary benefit of this work will be to develop more efficient markets (Defra objective 4) and the dissemination of knowledge gained will ultimately reduce suffering of animals (Defra Objective 8). A reduction in disease losses caused by this virus will ensure reasonably priced pork and beef (Defra Objective 10) which will directly assist the farming industry. This will also indirectly benefit the consumer by providing meat produced to a verifiable standard, at a competitive price.The association of PRRSV with respiratory disease and, more specifically, links with known opportunistic respiratory pathogens is well known. These secondary infections are controlled by administration of prophylactic and therapeutic antibiotics. This is of concern to the European Commission, whose Scientific Steering Committee has recommended a reduction of antibiotic use by disease preventive measures and removal of prophylactic antibiotic in feed. Also, the OIE International Standards on Antimicrobial Resistance advocates that antibiotics should be subject to prudent use by complying with the ethical obligation and economic need to keep animals in good health (Appendix 3.9.3, Objective 2), thereby reducing or eliminating the need for antibiotic use and that Regulatory Authorities have a responsibility to protect the environment from contamination with antimicrobials (Article, Section 9), also encouraging public-funded research to reduce such use (Section 15). This application, which will inform and allow more effective control of PRRSv, would therefore contribute to such reduction. This research also addresses one of Defra’s key aims for 2003-2006; the Science Directorate “Science and Innovation strategy for 2003-2006” states a requirement to identify and control risk factors associated with endemic non-zoonotic diseases and to examine new emerging diseases. Since it was first identified in 1991, PRRSV has grown in importance, such that it is now considered one of the major diseases of swine and the cause of significant economic loss, both directly, and indirectly, via its association with other viral and bacterial pathogens.
The exposure of the British pig herd to novel strains of PRRSV, both as a result of the evolution of existing strains and introduction of novel strains from Eastern Europe is increasingly likely. Novel strains have already been described in Accession countries and the drive to cut meat and production costs makes the likelihood of movements of pig products from such countries a real possibility. The scientific aims of this project are to obtain comprehensive information on the type(s) and diversity of strains of PRRSV circulating in the British pig herds in Britain and to asses the likely degree of protection from clinical disease afforded by a licensed live vaccine to PRRSV. The main objectives of the research will be:1. To establish the genetic sequence of ORF 7 of PRRS viral RNA from samples obtained from up to 100 clinical cases of respiratory and reproductive disorders in pig herds, and also from herds with other chronic or acute disease problems of unknown or complex aetiology. The sequences will be compared and their degree of diversity will be quantified.2. To obtain isolates of novel strains identified in Objective 1 and establish whether they are linked to any overt or novel disease. This will involve a more detailed analysis of selected regions of the viral genome. The isolates themselves will allow an assessment of diagnostic efficiency, forming part of Objective 3. Clinical investigations will provide an assessment of their ability to cause clinical disease. Where severe disease is observed by novel strains, we will plan to perform experimental infections, but these are outside the scope of this project.3. To measure the ability of currently used diagnostic tests to detect these viruses, and antibody induced by them. We will assess the ability of selected isolates to grow in different cell lines and will also measure reactivity of convalescent sera in homologous and heterologous antibody assays. We will also raise monospecific antisera using up to four diverse isolates and a vaccine, for use in future diagnosis.
Project Documents
• Final Report : Porcine reproductive and respiratory syndrome virus: emergence of novel strains in Britain   (3586k)
Time-Scale and Cost
From: 2005

To: 2008

Cost: £178,996
Contractor / Funded Organisations
Veterinary Laboratories Agency
Animal Diseases              
Animal Health              
Plants and Animals              
Veterinary Surveillance              
Fields of Study
Animal Health