PCV2 Vaccines

May 4, 2010

Update on Use of PCV2 Vaccines

PCVAD outbreaks emerged in North America during 2005-2006. The main PCV2 subtype isolated from these outbreaks changed from predominately PCV2a prior to 2005 to predominately PCV2b after 2006. PCV2b was not observed in North America prior to 2005. PCV2 vaccination was introduced in 2006 and it is estimated that nearly 99% of all growing pigs in the U.S. are now vaccinated with a commercial vaccine for PCV2. Two of the three commercial vaccines used are based on an open-reading-frame 2 (ORF2) protein expressed in the baculovirus system (BIVI, Intervet-Schering-Plough) whereas one vaccine (FDAH/Pfizer) is based on a chimeric PCV1-2 virus (ORF1 from PCV1 and ORF2 from PCV2). All three vaccines are killed and all are based on PCV2a.

Recently a chimeric PCV1-2a isolate was identified by PCR in Canadian pig tissue homogenates (Gagnon et al., 2010). This has raised concern about the possibility that this isolate originated in the FDAH/Pfizer Suvaxyn PCV2 vaccine.  As a precautionary measure, Pfizer Animal Health has taken action to temporarily remove the vaccine from the market to further investigate this possibility.  As the industry and profession work through this process it is important to consider some history and information that may not be widely known.  The FDAH/Pfizer product is based on a chimeric virus which means it is part PCV1 and part PCV2.  It was constructed in this manner originally so that it could be used as a modified live vaccine thereby giving it the non-virulent characteristics of PCV1 and the antigenic portion (ORF2) of PCV2 to provide broad cross-protection.  All studies to date have demonstrated that the live PCV1-2 chimeric version of the current FDAH/Pfizer killed vaccine is safe in pigs and induces protection against PCV2 (Fenaux et al., 2004; Gillespie et al., 2008; Segales et al., 2009). 

New Tests at ISU VDL to Answer Your Diagnostic Questions

The ISU VDL has a full menu of PCV diagnostic assays to assist in answering your questions.  A list of those assays and how they can be used is as follows:

• PCV1 real-time PCR: This assay is designed to detect the non-pathogenic PCV1.
• Quantitative PCV2 real-time PCR: This assay is based on PCV2 ORF1 which is highly conserved among PCV2 strains. It will pick up all different subtypes of PCV2 without differentiation.
• Quantitative PCV2a/b multiplex real-time PCR: This assay is based on the signature motif located in PCV2 ORF2. By using this assay it is possible to determine if PCV2a, PCV2b or a mixed PCV2a and PCV2b infection is present.
• Quantitative PCV1-2 real-time PCR: This assay targets the overlapping region of the chimeric PCV1-2 virus and is specific for PCV1-2. It will not cross-react with PCV1 or PCV2.

References

Fenaux M, Opriessnig T, Halbur PG, Elvinger F, Meng XJ.  A chimeric porcine circovirus (PCV) with the immunogenic capsid gene of the pathogenic PCV type 2 (PCV2) cloned into the genomic backbone of the nonpathogenic PCV1 induces protective immunity against PCV2 infection in pigs. Journal of Virology. 78:6297-6303, 2004.

Gagnon CA, Music N, Fontaine G, Tremblay D, Harel J.  Emergence of a new type of porcine circovirus in swine (PCV): A type 1 and type 2 PCV recombinant. Vet Microbiology (2010) doi:10.1016/j.vetmic2009.09.072.

Gillespie J, Juhan NM, DiCristina J, Key KF, Ramamoorthy S, Meng XJ.  A genetically engineered chimeric vaccine against porcine circovirus type 2 (PCV2) is genetically stable in vitro and in vivo.  Vaccine 26:4231-6, 2008.

Segales J, Urniza A, Alegre A, Bru T, Crisci E, Nofrarias M, Lopez-Soria S, Balasch M, Sibila M, Xu Z, Chu H-J, Fraile L, Plana-Duran J.  A genetically engineered chimeric vaccine against porcine circovirus type 2 (PCV2) improves clinical, pathological and virological outcomes in postweaning multisystemic wasting syndrome affected farms.  Vaccine 27:7313-7321, 2009.