USA – PCV4, a relatively new strain of Porcine circovirus-associated disease, has been detected in the USA, posing a significant challenge to swine health and pork production worldwide.
Known types like PCV2 and PCV3 have been extensively documented worldwide. However, the new player in this landscape, PCV4, has only been detected in China, Mongolia, South Korea, Thailand, and Malaysia.
This discovery marks a critical development in understanding porcine circovirus and its impact on the swine industry.
The detection of PCV4 in U.S. clinical samples was part of a study funded by the Swine Health Information Center and conducted by researchers at Iowa State University’s Veterinary Diagnostic Laboratory (VDL).
The samples, collected between June and September 2023, provide the first insight into the prevalence and tissue distribution of PCV4 within the U.S. and its potential role in swine disease and production losses.
Dr Pablo Pineyro’s research team examined 512 porcine samples, including lung, faeces, spleen, serum, lymphoid, and fetal tissue. PCV4 was detected in 8.6% of these samples, with the highest detection rates found in lymphoid tissue (17.2%).
The virus was most commonly identified in nursery to finishing aged pigs exhibiting respiratory and enteric disease.
Notably, co-infection with other pathogens, such as PCV2, PCV3, and various bacterial species, was frequently observed, complicating the clinical picture and highlighting the complex interplay between different porcine circoviruses.
The study also delved into PCV4’s molecular characteristics, with two complete ORF2 sequences obtained from U.S. samples showing high nucleotide identity with strains previously identified in Spain and South Korea.
This suggests a potential global dissemination of PCV4 strains, raising concerns about its spread and impact beyond the U.S.
Despite its detection, the pathogenesis of PCV4 remains poorly understood. The study found that while PCV4 was present in various tissues, it was notably absent in fetal samples, contrasting with reports from other countries where PCV4 has been detected in aborted fetuses.
This difference points to potential variations in tissue tropism and clinical presentation between PCV4 and its counterparts, PCV2 and PCV3.
The research underscores the need for further studies to assess the prevalence of PCV4, its role in coinfections, and its potential economic impact on the swine industry.
With PCV4 frequently co-detected alongside other pathogens, the study suggests that PCV4 may contribute to disease pathogenesis in conjunction with other viruses and bacteria, particularly in cases of respiratory and enteric diseases.
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