Porcine circoviruses--small but powerful.

When porcine circovirus type 1 (PCV1) was isolated more than 40 years ago as a non-pathogenic contaminant of a porcine kidney cell line, enthusiasm and curiosity kept within reasonable limits. Virologists became more interested, when a second variant was isolated and termed PCV2, because PCV2 is linked to postweaning multisystemic wasting disease (PMWS), a new emerging multifactorial disease in swine. Both PCV1 and PCV2 are small and rather simply organized and express only few proteins. Therefore, it was expected that the factor(s) triggering PMWS should be easily identified, but more than one decade of PCV research has not yet singled out a molecule inducing the disease onset. Unravelling the molecular features of PCV and the channels through which the virus interacts with its host are key to manage, prevent and treat PMWS and other PCV-associated diseases. Since we have learned many aspects of the molecular biology of PCV in the last years, it is time for a résumé!