Pathogenesis and Why Viremia Matters

PCV2 pathogenesis is how the disease develops within the pig. Following exposure to the virus, PCV2 viremia (presence of PCV2 in the blood) starts building and circulating in the blood and is the initial step in the development of the disease in the pig. It can last up to 4 to 5 months post-infection, causing prolonged shedding and increased challenge to all of the pigs in the group.

Even low levels of PCV2 viremia can have a metabolic cost. A pig's energy and resources are directed to the immune system rather than growth, affecting average daily gain and feed efficiency.

Because PCV2 infects the cells of the pig's immune system, the impact goes beyond the direct infection. Preventing PCV2 viremia also helps reduce the risk of co-infection from porcine reproductive and respiratory syndrome (PRRS), Mycoplasma hyopneumoniae and swine influenza virus (SIV).

Controlling PCV2 disease by utilizing vaccines that are labeled to help prevent viremia is a highly effective approach because the cycle of the disease is broken and the damage caused by infection is limited or essentially eliminated. Circumvent G2 has an "aid in prevention of viremia" label claim. Merck Animal Health believes viremia is the most important measure of PCV2 vaccine efficacy, as prevention of viremia stops the infection early on in the disease process before tissue damage can occur.

Also important are subsequent claims on the label. Those vaccines that reduce virus shedding and reduce lymphoid infection caused by PCV2 help stem the impact of infection that occurs later in the disease progression. The "aid in reduction" label claims mean that the vaccine in vaccinates significantly reduced the severity of virus shedding and lymphoid infection compared to controls.

Learn more in the Understanding PCV2 Pathogenesis Tech Bulletin. Download PDF