Data from 187 finishing herds shows that PCV2 is nearly universally present as an active infection in finishing herds, often at moderate to high levels of viremia in the presence of anti-capsid antibodies. PCV2a and PCV2b genotypes were widely distributed, with one or the other usually in different pigs on the same site, but as a dual infection nearly 10% of the time. Average viral titer was the same in animals infected with PCV2a, or PCV2b or both genotypes. Unexpectedly, PCV1 was essentially absent from swine, contrary to statements often found in the literature. The findings suggest that all of the conditions attributed to PCV-AD, including virulent genotypes and high viral titers, were commonly observed in the U.S. swine herd in 2006, and that anti-PCV immune responses also were present. Thus, it is surprising that PCV-AD was not more prevalent until recent times, and that capsid-based vaccines provide effective protection against PCV-AD. It appears that PCV2 by itself does not cause PCV-AD, but that it plays a role that has not yet been figured out.
Contact information: Michael Murtaugh, Department of Veterinary and Biomedical Sciences, University of Minnesota, 1971 Commonwealth Avenue, St. Paul, MN 55108. Phone: 612 625 6735, fax 612 625 5203. email: email@example.com