This disease causes illness in piglets, with clinical signs including progressive loss of body condition, visibly enlarged lymph nodes, difficulty in breathing, and sometimes diarrhea, pale skin, and jaundice.

[1] For example, concurrent infection with porcine parvovirus or PRRS virus, or immunostimulation lead to increased replication of PCV-2 and more severe disease in PCV-2-infected pigs.

Porcine circovirus type 1 (PCV1) was first identified in 1974 and was recognized as a non-disease-causing agent that frequently occurred in laboratory tissue cultures.

[8] Many pigs affected by the circovirus also seem to develop secondary bacterial infections, like Glässer disease (Haemophilus parasuis), pulmonary pasteurellosis, colibacilosis, salmonellosis and others.

[9] Postmortem lesions occur in multiple organs, especially in lymphoid tissues and lung, giving rise to the term "multisystemic".