Control of Porcine Circovirus Disease (PCVD)
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Research partners: The Queen’s University of Belfast, Merial SAS (France), Ghent University, Danish Institute for Food and Veterinary Research, Institute of Virology and Immunoprophylaxis (Switzerland), University of Saskatchewan, Robert Kochinstitut (Germany), Royal Veterinary and Agricultural University (Denmark), Sverige Lantbruksuniversitet (Sweden), ID-Lelystad (Netherlands), Devenish Nutrition Ltd, Centre de Recerca en Sanitat Animal (Spain), BPEX, Agence Française de Sécurité Sanitaire des Aliments, Danish Bacon and Meat Council, Veterinary Research Institute (Czech Republic), National Veterinary Research Institute (Poland), Kosice University of Veterinary Medicine (Slovakia), Szent Istvan University (Hungary), Croatian Veterinary Institute
Sponsors: EU Framework 6
Project duration: 2004 - 2009
The objective of this project is to generate scientifically sound information on the causes and the early development of Porcine Circovirus Diseases (PCVDs). This information will be used to develop control measures that will have a positive impact on the health and welfare of pigs.
Many pig farmers know only too well the major impact of PMWS on the health and welfare of their pigs and the serious consequences of it for farm profitability. PMWS is caused by infection with Porcine Circovirus 2 (PCV2), but the virus alone is not enough to create problems in a herd. Factors such as management and feeding also play a part in disease development. This project established an EU-led multidisciplinary consortium containing expertise in epidemiology, pig genetics, pig nutrition, pathology, molecular biology, immunology, vaccinology, bacteriology and PCV virology to generate scientifically sound information on the aetiology and early pathogenesis of porcine circovirus diseases (PCVDs).
PCV2 genotypes
The EU Consortium has developed a scientific definition for PCV2 genotypes in order to standardize nomenclature. The methodology is based on the proportion of nucleotide sites at which two sequences being compared are different. Using this system, three genotypes can be defined based on sequences in the GenBank database.
A study on PCVDs in Sweden, in 2005, suggested that a particular genogroup (SG3) was usually associated with PMWS occurrence, while others (SG1 and SG2) were usually not. In Canada, a restriction fragment length polymorphism (RFLP) pattern (321-like) of PCV2 was associated with severe disease outbreaks, while the RFLP pattern 422-like was linked to sporadic occurrence of PCVD. Further studies on potential pathogenicity differences among PCV2 isolates by the EU Consortium on PCVDs in Denmark and Spain also support such differences.
Resistance and susceptibility to PMWS
Other observations have indicated that part of the explanation for why some pigs are more severely affected by the virus than others could be an inheritable natural resistance or an inheritable increased susceptibility to PCV2.
The heritability of PMWS susceptibility is being investigated and aims to identify genes that influence PMWS susceptibility. The ultimate goal is to develop a genetic test to be used for selection of PMWS resistant breeding animals and thereby minimize or eliminate the problems with PMWS in pig breeding and production. Work is ongoing but it is already clear that at least one gene seems to have quite a big effect on disease development. A good candidate gene has been identified but it is still too early to say how central this gene is for the development of PMWS, and also whether it is important in all pigs or just in some populations. For the same reason it cannot yet be said if this gene can form the basis for a genetic test that can be useful in selection of breeding animals. This research project has, nevertheless, looked at PMWS from a new angle that, together with other results in this EU research program, has given us a new and unique viewpoint in the quest to understand PMWS better.
PCV2 and the foetus
Researchers in Belgium have shown that different PCV2 strains replicate to similar high titres in different foetal organs and induce comparable gross pathological lesions. They have demonstrated that the clinical outcome of a PCV2 infection at 55 days of gestation is independent of the genotype and the clinical origin of the PCV2 strain. Indications that PCV2 may spread to non-inoculated foetuses were not found.
PMWS Transmission
Transmission studies in Denmark have shown that it is possible to transmit PMWS from pigs originating from PMWS-affected herds to pigs from a PMWS non-affected herd over short distance without direct contact. Another study concluded that PMWS can be transmitted to healthy pigs after mingling with pigs from PMWS affected herds. As PMWS seems to be transmitted from pig to pig both by close contact and by the airborne route pigs with clinical symptoms of PMWS should be removed from healthy pigs, mingling of pigs with PMWS and healthy pigs should be avoided and biosecurity measures should be taken to avoid the spread of PMWS.
Further information
Further information can be found on the project website ( www.pcvd.net ) and there is also a PCVD Discussion forum that is operated jointly with the PigSite (www.thepigsite.com).