company news about A novel porcine circovirus, PCV5, has been discovered! It is closely associated with respiratory and diarrheal diseases.

On October 8, 2025, a team from the College of Animal Science at South China Agricultural University published their latest research in the internationally renowned microbiology journal *Microbiology Spectrum*, identifying and systematically analyzing a novel porcine circovirus—PCV5—closely associated with respiratory diseases, diarrhea, and reproductive disorders in pigs.

Research Highlights

* **Novel Virus:** PCV5 shows low homology (only 26.2%) with known PCV1–PCV4 in terms of genomic structure, Rep, and Cap protein sequences. Phylogenetic analysis indicates it does not belong to the Circoviridae family but is most closely related to seal fecal-associated circoviruses.

* **Wide Prevalence:** In 70 pig farms across five southern provinces of my country, PCV5 was detected in 24.3% of the farms, and serological testing showed that 66.84% of pigs carried PCV5 antibodies.

* **Strong Pathogenicity:** PCV5 viral load is positively correlated with disease severity, with high viral loads observed in the gut and brain tissue, suggesting its potential ability to cross the blood-brain barrier.

• Technological Breakthrough: The research team successfully established an in vitro culture system for PCV5, purified viral particles with a diameter of approximately 20 nm, and developed a highly sensitive ELISA detection method by utilizing truncated Cap proteins to self-assemble into virus-like particles.

This research, jointly funded by the Guangdong Provincial Agricultural Breeding Technology Innovation Project and the National Key Research and Development Program, saw the research team complete the epidemiological survey, genome analysis, in vitro culture, and pathogenicity analysis of PCV5 after more than two years of systematic research. The findings provide crucial data for a deeper understanding of the evolution and pathogenic mechanisms of CRESS DNA viruses.

Introduction

Porcine circoviruses (PCVs) have long been a significant pathogen in swine diseases globally. PCV2, PCV3, and PCV4 are known to cause severe losses, including immunosuppression, dermatitis-nephropathy, and reproductive disorders. This study indicates that existing circovirus control systems in pig farms are facing new challenges.

Research Results

1. Epidemiological Characteristics:

From October 2021 to June 2023, the research team conducted monitoring in 70 pig farms across five provinces: Guangdong, Guangxi, Hunan, Yunnan, and Hainan. PCV5 positivity was detected in 17 pig farms. Serological surveys showed that 66.84% of the pig herds had PCV5 antibodies, with a positive rate as high as 71.37% in sows.

Figure 1. Geographical distribution and genome structure of PCV5

(A) The blue area represents the region where PCV5 was monitored, and the red circles indicate the locations of pig farms confirmed to be infected with PCV5. A total of 17 pig farms in Guangxi, Guangdong, Hunan, Yunnan, and Hainan provinces tested positive for PCV5. (B) PCV5 has a single-stranded circular genome (2904 nt), including the Cap gene (1182 nt), the Rep gene (1056 nt), and a stem-loop structure (stem: 9 nt, loop: 17 nt).

2. Genome and Evolutionary Characteristics:

The PCV5 genome is 2904 nt in length, containing longer Cap (1182 nt) and Rep (1056 nt) gene regions and extended stem-loop structures. Its Rep and Cap proteins share only 26.2% and 20.8% amino acid homology with known PCV family members, respectively. Evolutionarily, it is most closely related to sea lion-associated circovirus (FSfaCV). The Cap protein similarity between 12 PCV5 strains and FSfaCV ranges from 89.1% to 99.2%.

Figure 2. Subcellular localization of PCV5 Cap and Rep

Figure 3. Genetic relationships between PCV5 strains and PCV1, PCV2, PCV3, PCV4, PCLV, and several human circoviruses.

The amino acid sequence identity of the Rep (A) and Cap (B) sequences of 12 PCV5 strains with other circoviruses. Black asterisks represent PCV1, PCV2, PCV3, PCV4, and PCLV, and blue circles represent the FSfaCV strain (accession number KF246569.1).

Figure 4. Phylogenetic tree constructed based on the amino acid sequence of the Rep protein of CRESS DNA virus.

PCV5 strains are marked with red circles, and black circles represent five porcine circoviruses: PCV1, PCV2, PCV3, PCV4, and PCLV.

3. Biochemical and morphological characteristics:

The PCV5 Rep protein possesses the typical endonuclease, oligomerization, and helicase domains of CRESS DNA viruses, and exhibits ATPase activity; the virus particles are non-enveloped icosahedral, approximately 20 nm in diameter, and the truncated Cap protein can self-assemble into virus-like particles.

Figure 5. Soluble expression of PCV5 Rep and determination of ATPase activity

(A) Structural comparison of PCV5 Rep and PCV2 Rep. Blue, cyan, yellow, and orange represent extremely high, reliable, low, and extremely low predicted local distance difference test (pLDDT) scores, respectively (pLDDT range 0-100, reflecting residue confidence distribution). N and C represent the N-terminus and C-terminus of the protein, respectively.
(B) Electrophoresis results of the full-length PCV5 Rep. M is the protein molecular weight marker. Lane 1 is the sample before induction, lane 2 is the sample after induction, lane 3 is the supernatant sample after induction, and lane 4 is the precipitate sample after induction.
(C) PCV5 Rep Stable expression of NΔ118 in the PGEX-GST plasmid prokaryotic system; lane 1: sample before induction; lane 2: precipitate after induction; lane 3: nickel column permeation buffer; lanes 4-6: 30mM, 50mM, and 300mM imidazole elution buffers, respectively; (D) Protein concentration and electrophoresis results after molecular sieve purification; (E) ATPase activity assay of PCV5 Rep NΔ118.

4. Evidence of Pathogenicity:

PCV5 is associated with respiratory disease, diarrhea, and reproductive disorders in piglets and can cause porcine circovirus-associated disease (PCVAD). It widely infects multiple organs, including the heart, liver, spleen, lungs, kidneys, brain, and intestines, and can cross the blood-brain barrier; viral copy number is closely related to disease severity, with the most significant damage occurring in the ileum. Mice infected with PCV5 show no clinical symptoms and the virus is undetectable, making them unsuitable as a PCV5 disease model.

Figure 6. CT values ​​of PCV5 virus in organs of 12 piglets

Summary

This study not only confirmed the existence and pathogenicity of PCV5 for the first time, but also broke the existing classification framework of porcine circoviruses, providing a new perspective for the study of the diversity of CRESS DNA viruses. The high prevalence and widespread pathogenicity of PCV5 in South China pose new challenges to the current prevention and control system for porcine circovirus disease, and also lay the foundation for the development of targeted diagnostic reagents and vaccines.

Future research will further clarify the transmission routes of PCV5, the risk of cross-species infection, and the co-infection mechanisms with other pathogens, providing theoretical support for the formulation of scientific prevention and control strategies.