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Research on Porcine Circovirus-Associated Diseases

by 5m Editor
12 August 2009, at 12:00am

A review of current projects researching Porcine Circovirus-Associated Disease (PCVAD) from the BPEX Annual Technical Report 2008-2009.

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.

The 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 standardise 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.

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 minimise or eliminate the problems with PMWS in pig breeding and production. Work is on-going 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 programme, 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.

August 2009