Porcine Circovirus type 2 (PCV2) causes post-weaning multisystemic wasting syndrome (PMWS), which causes clinical signs usually in pigs 7-15 weeks of age. The 2004-2005 outbreak in eastern Canada affected older hogs, though. This outbreak may also be caused by a novel strain of PCV2. PCV2 is necessary for causing PMWS, but other co-factors are involved as well. These can include the presence of other diseases, immune functioning, and production practises. Most commercial pigs have low levels of PCV2 and remain healthy; those that do develop PMWS have very high levels of PCV2. Keeping PCV2 levels below the threshold could prevent PMWS. Vaccines are currently not available, but are being developed.