SHIC Updates PCV3 Fact Sheet and Pursues Case Definition

The Swine Heath Information Center has updated its porcine circovirus 3 Fact Sheet and begun a project with Iowa State University and the University of Minnesota to investigate historical submissions, tests, and tissues, with their available clinical signalment, to help lead to an applicable US case definition. An analysis of historical submission tests/clinical signs at UMN has already been done and will add to the case definition development. The laboratory analyses will help lead to standardized diagnostic criteria and when the case definition is finalized, on-farm epidemiological work will begin later in 2022.

PCV3 is an emerging pathogen of swine with potential economic importance, per SHIC’s updated PCV3 Fact Sheet. It has been associated with signs similar to those caused by PCV2. However, many infections seem to be subclinical, and PCV3 pathogenicity studies have had mixed results. PCV 3 has been associated with neurological disease, reproductive failure, respiratory disease, enteric disease, and porcine dermatitis and nephropathy syndrome. However, only a few studies have demonstrated the presence of PCV3 in lesions.

Both PCV2 and PCV3 spread through vertical and horizontal transmission. Virus is shed in most secretions and excretions. Direct contact is the route of most significance but spread can also occur via fomites and ingestion. PCV3 is found in wild and domestic pigs. Antibodies to PCV3 have been detected in dogs, cattle, and mice. PCV3-positive mosquitoes have been found. Wild ruminants and ticks may also be reservoirs.

PCV3 is found in many swine-producing regions of the world. Epidemiological studies have found that infection is widespread, with prevalence up to 100%. Little is known about the course of natural infection. A few studies have shown that prevalence is highest in piglets/weaners and decreases with age, but PCV3 has been detected in pigs up to 23 weeks of age.

PCV3 belongs to the family Circoviridae. Members are very small, non-enveloped viruses with a circular, covalently closed, single-stranded DNA genome. While there are four recognized circoviruses of swine, designated PCV1–4, PCV3 is distinctly different from other PCVs and is closely related to canine and bat circoviruses.

PCV1 was identified in 1974 as a contaminant in a pig kidney cell line. In 1997, PCV2 was recognized as the cause of a novel wasting disease affecting Canadian pigs. In 2016, PCV3 was detected in tissues from sows from North Carolina that died acutely with PDNS-like clinical signs and aborted fetuses. PCV4 was discovered in samples from pigs with respiratory disease, enteric disease, and PDNS in China in 2019.

SHIC, launched by the National Pork Board in 2015 solely with Pork Checkoff funding, continues to focus efforts on prevention, preparedness, and response to novel and emerging swine disease for the benefit of US swine health. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. SHIC is funded by America’s pork producers to fulfill its mission to protect and enhance the health of the US swine herd. For more information, visit http://www.swinehealth.org or contact Dr. Sundberg at psundberg@swinehealth.org.