SHIC-Supported PCV3 Clinical Sign and Pathology Investigation Informs Case Definition Work

A SHIC-funded report evaluating diagnostic data on porcine circovirus type 3 obtained during 2016-2018 by the University of Minnesota Veterinary Diagnostic Lab has been posted. Under the direction of Dr. Albert Rovira, the study objectives were to determine associations between PCV3 presence and quantity with lesions and clinical signs. Results showed PCV3 may cause death in fetuses, myocarditis, and systemic vasculitis in pigs. This data is helping to contribute to an ongoing SHIC-funded study to determine an applicable US case definition.

PCV3 was first identified in the US in 2016, associated with cases of systemic disease and reproductive disorders. Multiple studies performed after its discovery showed PCV3 is widespread and has been present in the US pig herd for decades. It can be found in multiple tissues and samples, as well as in pigs with clinical disease and in healthy pigs. Overall, the role of PCV3 in causing disease is poorly defined.

In the newly posted Rovira study, the relationship between PCV3 antigen and clinical disease was investigated based on a large dataset of diagnostic cases. PCV3 was detected in approximately 20% of pigs with tissues submitted to the UMN diagnostic laboratory. Samples with the highest PCV3 quantity were detected in fetal lesions of myocarditis and systemic vasculitis. Although no significant associations were identified between PCV3 antigen detection with the clinical description on VDL submissions, there was a significant association between PCV3 presence and heart vasculitis/perivasculitis. In PCV3-positive pigs, higher viral loads were significantly associated with pigs having myocarditis, heart vasculitis/perivasculitis, kidney vasculitis/perivasculitis and dermatitis. 

Following publication of the Rovira study, SHIC updated its PCV3 Fact Sheet. In it, PCV3 is categorized as an emerging pathogen of swine with potential economic importance. It has been associated with signs similar to those caused by PCV2, including subclinical infections. Overall, PCV3 has been associated with neurological disease, reproductive failure, respiratory disease, enteric disease, and porcine dermatitis and nephropathy syndrome.

Both PCV2 and PCV3 are spread through vertical and horizontal transmission. Virus is shed in most secretions and excretions of infected pigs. Direct contact is the transmission route of most significance but spread can also occur via fomites and ingestion. PCV3 has been found in both 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%. A few studies have shown that prevalence is highest in piglets/weaners and decreases with age, but PCV3 has been detected in pigs of all ages.

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. Paul Sundberg at psundberg@swinehealth.org.