A study on porcine circovirus type 3 (PCV3) funded by the Swine Health Information Center (SHIC) mined diagnostic data obtained by the University of Minnesota Veterinary Diagnostic Lab (UMN VDL) during the last two years to identify associations between the presence of PCV3 and its viral load, and specific lesions and clinical conditions. Results from this study suggest PCV3 may cause death in fetuses and myocarditis and systemic vasculitis in pigs. PCV3 was discovered in 2016 in the US, associated with cases of systemic disease and reproductive disorders. Multiple studies performed during the last two years have shown that this virus is widespread and has been around for decades. It can be found in multiple tissues and samples, in pigs with multiple clinical conditions and in healthy pigs. However, a lack of precise information on the relevance of this virus and its potential to cause disease in pigs existed.
PCV3 results, clinical signs, and information on the lesions for each pig were retrieved from the UMN VDL lab information management system, submission forms, and diagnostic reports. PCV3 frequency in pigs with different clinical signs ranged from 12% to 27%. No significant associations were observed between clinical signs and the presence of PCV3. In PCV3-positive pigs, no clinical signs were significantly associated with having a higher load of PCV3. PCV3 frequency in pigs with different lesions ranged from 0% to 62%.
Even though this study did not identify any significant associations with clinical signs, the lesion that had a significant association between its presence and PCV3 infection was heart vasculitis/perivasculitis. In PCV3-positive pigs, higher viral loads were significantly associated with pigs with myocarditis, heart vasculitis/perivasculitis, kidney vasculitis/perivasculitis and dermatitis.
And the presence of PCV3 in 20% of cases involving fetuses is remarkable. The samples with the highest PCV3 concentration in this study were from fetal tissues and lesions of myocarditis and systemic vasculitis were associated with the presence or the amount of PCV3 in these tissues. The lack of significant results for other lesions does not exclude the possibility of a real association and may be due to confounding factors or limited data.
In summary, this study provides an objective view of the relationship between PCV3 and disease, based on a large dataset of diagnostic cases. PCV3 is a very common virus that circulates in healthy populations and can be detected in around 20% of the pigs submitted to the diagnostic laboratory. Therefore, it is important to differentiate when PCV3 plays a significant role and when it does not. The results from this study support previous studies that suggested that PCV3 may cause death in fetuses and myocarditis and systemic vasculitis in pigs.
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