PCV2 is associated with a wide variety of combinations of clinical disease that include reproductive failure, porcine dermatitis and nephropathy syndrome (PDNS), respiratory and systemic disease. The discovery of PCV3 virus in cases that clinically resembled PCV2 has lead to some widespread surveillance activity. One of the findings has been that the PCV3 virus is much more widespread than first suspected. The virus was found in many herds that have not had evidence of circovirus disease. In order to truly say that PCV3 is causing clinical disease and is not just an “innocent bystander” it is necessary to demonstrate that the affected pig is showing clinical signs of the disease, the pathological lesions are present microscopically and that the virus can be identified within the affected tissues.
The investigators in this study documented thirty-six field cases that were submitted from multiple production systems, numerous sites and varied geographic locations. They were able to demonstrate PCV3 virus within affected tissues by using an “in situ hybridization” test in fetuses with myocarditis, weak-born neonatal piglets with encephalitis and myocarditis, from cases of porcine dermatitis and nephropathy syndrome, and in weaned pigs with systemic periarteritis. PCV3 was detected by PCR in numerous fetuses and perinatal piglets at high viral loads. Samples from all cases in this study were assayed and found negative for PCV2 by PCR. Metagenomic sequencing was performed on a subset of reproductive cases, consisting of sixteen fetuses/fetal sample pools. PCV3 was identified in all pools and it was the only virus identified in fourteen pools.
Take Home Message
These particular clinical cases appear to be associated with PCV3 infection.
Thankfully, clinical disease associated with PCV3 is not occurring on a frequent basis. We will however need to monitor this closely as PCV2 started with a “wimper and not a bang!”
Submitted by Clint Lichty, DVM
Ref: Arruda B, Piñeyro P, Derscheid R, Hause B, Byers E, Dion K, Long D, Sievers C, Tangen J, Williams T, Schwartz K.PCV3-associated disease in the United States swine herd.Emerg Microbes Infect. 2019;8(1):684-698. doi: 10.1080/22221751.2019.1613176.