Genetic diversity of porcine circovirus type 2 and implications for detection and control

• Porcine circovirus type 2 [PCV2] is an economically important swine pathogen.
• Recently, several new PCV2 strains and recombinants have emerged.
• Mutation and recombination play a role in viral evolution.
• Vaccine induced selection pressure may also drive evolution.
• Updating current PCV2 vaccines will likely improve immunity and reduce selection pressure.

Porcine circovirus type 2 (PCV2) is the etiological agent of post- weaning multi-systemic wasting syndrome (PMWS), an economically important disease of swine. Severe wasting and lymphadenopathy are typical signs of PMWS. Effective vaccines against PCV2 and reliable diagnostic tests are available. Since PCV2's discovery in the mid-90s and the introduction of commercial vaccines, several new recombinant strains and variants with genetic mutations have emerged. Two noteworthy changes include; a major type switching event that resulted in the previously predominant PCV2a genotype being replaced by PCV2b, and the recent emergence of a mutant PCV2b with a capsid protein containing an additional lysine. The mutant PCV2b exhibits increased virulence and is spreading rapidly in various regions of the world. This article provides an overview of the recent molecular epidemiology in the context of the current methods for the detection and prevention of PCV2, emphasizing the need for updated PCV2 vaccines.