First detection and genomic analysis of canine circovirus in a dog with hemorrhagic diarrhea in South Korea: a case report

Article information

Korean J Vet Res. 2025;65.e24

Publication date (electronic) : 2025 December 31

doi : https://doi.org/10.14405/kjvr.20250029

Seulgi Hwang^1,†, Thu Ha Nguyen^2,†, Mahmoud Soliman³, You-Chan Bae⁴, Kwang-Soo Lyoo⁵, Hayoung Ryu¹, Seongwon Heo¹, Hyeona Bae¹, Kyoung-Oh Cho^2,, DoHyeon Yu^1,

¹College of Veterinary Medicine, Gyeongsang National University, Jinju 52828, Korea

²Host-Directed Antiviral Research Center, Chonnam National University, Gwangju 61186, Korea

³Department of Pathology & Clinical Pathology, Faculty of Veterinary Medicine, Assiut University, Assiut 71515, Egypt

⁴Animal Disease Diagnostic Division, Animal and Plant Quarantine Agency, Gimcheon 39660, Korea

⁵Department of Veterinary Nursing, College of Health Sciences, Wonkwang University, Iksan 54538, Korea

^*Corresponding author: Kyoung-Oh Cho Host-Directed Antiviral Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, Korea Tel: +82-62-530-2845 E-mail: choko@jnu.ac.kr

^*DoHyeon Yu College of Veterinary Medicine, Gyeongsang National University, 501 Jinju-daero, Jinju 52828, Korea Tel: +82-55-772-2368 E-mail: yudh@gnu.ac.kr

†These authors have contributed equally to this work and share the first authorship.

Received 2025 July 7; Revised 2025 November 7; Accepted 2025 November 29.

Canine circovirus (CanineCV) belongs to the genus Circovirus in the family Circoviridae. Circoviruses are small, non-enveloped viruses containing circular, single-stranded deoxyribonucleic acid (DNA) genome [1–3]. CanineCV was first detected in the serum of several dogs in the United States in 2012 [4], and has since been reported in the United States, Taiwan, China, Vietnam, Turkey, Iran, and Colombia [1,2,5–7].

The clinical signs associated with CanineCV infection in dogs include severe hemorrhagic gastroenteritis, vasculitis, and granulomatous lymphadenitis [5]. However, owing to reports on circovirus detection in samples from clinically healthy dogs, the pathogenesis and epidemiology of CanineCVs remain unclear [2,5,6,8].

This report describes the first detection and genomic classification of CanineCV strain in a dog with hemorrhagic diarrhea in South Korea.

A 5-year-old male Golden Retriever presented with acute diarrhea that lasted for 3 weeks; it appeared watery and bloody. Hematological analysis revealed moderate anemia, with a packed cell volume of 24% (reference range [ref.], 35%–55%), a reticulocytosis (19,800/μL), and neutrophilic leukocytosis (60.34 × 10³/μL; ref., 5.05–16.76 × 10³/μL) with a left shift (band neutrophils, 20,998 cells/μL) at initial presentation. Hypoalbuminemia (1.2 g/dL; ref., 2.3–4 g/dL) and hypoglobulinemia (2.1 g/dL; ref., 2.5–4.5 g/dL) suggested protein-losing enteropathy. The Canine Diarrhea RealPCR Panel from IDEXX Laboratories detected CanineCV, Campylobacter jejuni, and the Clostridium perfringens alpha-toxin gene. Despite symptomatic treatment with antibiotics, analgesics, and gastrointestinal protectants, the dog’s symptoms worsened, leading to humane euthanasia.

On necropsy, multiple severe suffusive and ecchymotic hemorrhages were observed throughout the skin and subcutaneous tissues. The intestinal mucosa showed moderate diffuse thickening with multiple hemorrhagic foci (Fig. 1A); however, the gastric mucosa remained relatively intact. The mesenteric lymph nodes were severely enlarged and contained cheese-like material (Fig. 1B and C). The lungs showed multiple severe, locally extensive areas of congestion throughout the lobes, where lung collapse had failed (Supplementary Fig. S1A). All liver lobes were brown and enlarged, indicating steatosis (Supplementary Fig. S1B). Both kidneys exhibited severe diffuse deep cortical pallor and medullary congestion (Supplementary Fig. S1C).

Fig. 1.

Gross and histopathological findings in a dog with Korean canine circoviral infection. (A) Jejunum. Moderate diffuse thickness of the jejunal mucosa. (B, C) Mesenteric lymph node (LN). Severely enlarged LN (B) with central cheese-like material on the cut surface (C). (A–C) Scale bars = 1 cm. (D, E) Jejunal mucosa. Severe diffuse infiltration of histiocytic lymphoid cells (D) with neutrophils, lymphocytes, and multinucleated giant cells (arrows), resulting in the disappearance of normal villous and crypt structures (arrowhead). (F, G) Jejunal submucosa. Severe diffuse infiltration with histiocytic lymphoid cells (F) and fibrinoid necrosis (arrow) (G). (H, I) The cortex of the mesenteric LN. Severe infiltration with histiocytes (H, low magnification; I, high magnification). (J, K) The medulla of the mesenteric LN. Severe diffuse coagulative necrosis of the lymphoid cells (J, low magnification; K, high magnification). (L) Mesenteric LN. Granulomatous lesion consisting mainly of histiocytes. Note the amphophilic intracytoplasmic inclusion bodies in the histiocyte. (D–L) Hematoxylin and eosin stain. Scale bars: D, F, H, J = 300 μm; E, G, I, K = 150 μm; L = 100 μm.

Formalin-fixed tissue samples were routinely processed for hematoxylin and eosin staining (3-μm sections). Microscopically, the mucosa and submucosa of the small intestine showed severe diffuse infiltration with histiocytic lymphoid cells, neutrophils, lymphocytes, and multinucleated giant cells, resulting in the disappearance of normal villous and crypt structures (Fig. 1D–G). Furthermore, fibrinoid necrosis of the blood vessels, characterized by the deposition of eosinophilic amorphous material in the vessel wall, known as fibrinoid vasculitis, was observed throughout the small intestine (Fig. 1G). In the mesenteric lymph nodes, the cortex exhibited multiple severe, locally extensive proliferations of histiocytic cells, along with a few lymphoid and erythroblast cells (Fig. 1H and I). The medulla contained coagulative necrotic cells (Fig. 1J and K). Some of the histiocytic cells in the granulomatous lesions contained round, intracytoplasmic, amphophilic inclusion bodies (Fig. 1L), which are strongly suggestive of CanineCV infection. The lungs showed multiple severe hemorrhages and areas of congestion, along with fibrinous and edematous exudates, as well as severe infiltration of alveolar macrophages into the alveolar lumen, where a thrombotic embolus had formed (Supplementary Fig. S1D and E). Severe, diffuse hepatocytic swelling with large lipid droplets was observed throughout the hepatic lobe (Supplementary Fig. S1F and G). The kidneys exhibited moderate diffuse glomerulonephritis and thrombotic emboli in the outer cortex, leading to severe tubular degeneration and inner cortical necrosis (Supplementary Fig. S1H and I).

The small intestine, mesenteric lymph nodes, and fecal samples were collected during the necropsy and used to extract RNA and DNA [5,7,9,10]. To consolidate the causes of viral enteritis examined above, we performed polymerase chain reaction (PCR), reverse transcription (RT)-PCR, or nested PCR targeting CanineCV, canine parvovirus, norovirus, coronavirus, distemper, rotavirus A, and astrovirus using their specific primer pairs (Supplementary Table S1) [6,11–15]. As a negative control and to avoid the amplicon carryover, we used distilled water. In this trial, only CanineCV was amplified in the jejunum, mesenteric lymph node, and fecal sample, but not in the negative control, by PCR (Fig. 2A) using a primer pair specific to the partial region flanking the CanineCV replicase and capsid.

Fig. 2.

Molecular detection and characterization of Korean canine circovirus (CanineCV). (A) Detection of Korean CanineCV in the jejunum, mesenteric lymph node (LN), and fecal sample using polymerase chain reaction (PCR) with a primer pair specific to the partial region flanking the CanineCV replicase and capsid (1,756 bp). (B) Amplification of full-length capsid gene (810 bp) of Korean CanineCV from the jejunum and mesenteric LN using PCR with a primer pair specific to the CanineCV capsid. (C) Phylogenetic analysis of the full-length nucleotide sequence of Korean CanineCV with others.

For genomic characterization, the full-length capsid gene was amplified using its specific primer pair (Supplementary Table S1), cloned, and sequenced (Fig. 2B). Sequences were aligned with other reference strains (Supplementary Table S2) using Multiple Sequence Alignment by CLUSTALW [16] and compared with those of other known circoviruses [6,11–16]. Phylogenetic analysis of the full-length sequence of the Korean CanineCV capsid gene with other reference strains (Supplementary Tables S2) was performed using the neighbor-joining phylogenetic tree (1,000 bootstrap replicates) constructed using MEGA 11 software [17]. The full-length sequence of the Korean CanineCV (Canine CV Kr/Jinju/2021) capsid gene has been deposited in GenBank under the accession number (PX460959).

The full-length nucleotide and amino acid sequences of the capsid gene shared the highest homology with CanineCVs (85.1%–92.0% of the nucleotide sequences and 91.5%–94.4% of the amino acid sequences) (Table 1). In particular, Korean CanineCV showed 92.0% nucleotide sequence and 94.4% amino acid sequence homology with the UCD3-478 strain of the United States among CanineCVs. The present case also showed higher nucleotide and amino acid sequence homology with fox circoviruses of the same canine family than with circoviruses of other species (Table 1). Phylogenetic analysis of the complete nucleotide sequence of the capsid gene showed that Korean CanineCV belongs to type 4, and is closely related to the American UCD3-478 strain (Fig. 2C) [4,6,18]. In this case, only limited organ and tissue samples could be collected with the owner's permission, which prevented further examination of the bacteria identified by IDEXX Laboratories and their role in the development of the intestinal lesion.

Table 1.

Comparison of the full-length capsid gene sequences of Korean canine circovirus with other strains

CanineCVs have been reported in many countries [1]. To our knowledge, this is the first report of CanineCV-associated hemorrhagic diarrhea in South Korea, confirmed using genomic analysis.

CanineCV infects domestic and wild canids and is primarily associated with hemorrhagic enteritis in dogs [1]. The virus is not only detected in the fecal samples of apparently healthy dogs but is also frequently identified in co-infections with other pathogens [1–3,5,6,8]; PCR of fecal samples has identified CanineCV in dogs with diarrhea (11.3%–32.4%) and healthy dogs (6.9%–28.4%). Moreover, 68%–81.69% of dogs with diarrhea are coinfected with one or more other pathogens [5,8]. Therefore, the role of CanineCV as a primary pathogen or co-infecting agent in canine gastrointestinal diseases remains unclear. Coinfection with C. jejuni and the alpha-toxins of C. perfringens was also detected.

Coinfection of porcine circoviruses (PCVs) with other pathogens has been documented in pigs. PCV2 primarily targets the lymphoid tissues in pigs, destroying the lymphoid follicle structure and replacing depleted lymphocytes with histiocytic cells. As a result, PCV2 infection causes severe immunosuppression in pigs, increasing their vulnerability to secondary infections [19]. PCV2-induced post-weaning multisystemic wasting syndrome is often associated with coinfection by bacterial pathogens, especially Salmonella typhimurium, which can cause watery or occasionally bloody diarrhea [20]. Thus, CanineCV may induce immunosuppression, facilitating secondary bacterial infections.

Histopathological lesions were consistent with previous CanineCV reports. Li et al. [5] described fibrinonecrotizing vasculitis involving multiple organs, including the intestine, along with histiocytic drainage or granulomatous lymphadenitis in the Peyer’s patches and lymph nodes. In their study, cytoplasmic viral inclusions within histiocytes in the lymph nodes were identified using electron microscopy [5]. Fibrinoid vasculitis was also evident in our patient and accompanied by severe diffuse infiltration of histiocytic lymphoid cells into the intestinal lesions. Granulomatous lymphadenitis was observed in the mesenteric lymph nodes, characterized by histiocytic cells containing round, intracytoplasmic, amphophilic inclusion bodies. These findings are similar to those observed in pigs infected with PCV2, which is characterized by lymphocyte depletion, histiocytic infiltration, intracytoplasmic inclusion bodies, and multinucleated giant cells in lymphoid tissues [21]. These histopathological changes are thought to contribute to immunosuppression and increase susceptibility to secondary infections. Additionally, multiplex PCR analysis detected the C. perfringens alpha-toxin gene and the C. jejuni. C. jejuni can cause clinical signs ranging from asymptomatic carriage to diarrhea containing blood and mucus, often accompanied by mild-to-moderate lymphoplasmacytic enterocolitis. C. perfringens is associated with acute mucosal necrosis and neutrophilic infiltration [22]. While these pathogens may cause chronic inflammation, the presence of numerous intracytoplasmic inclusion bodies within the histiocytic cells of the mesenteric lymph nodes remains a strongly suggestive finding of CanineCV infection. Since the primary driver of enteric pathology in this single case (CanineCV vs. co-pathogens) is unknown, further detailed studies are needed.

Circoviruses are known to undergo frequent recombination between different genotypes and strains. However, the presence of potential recombination in this study was not performed, and this represents a limitation that should be considered when interpreting the phylogenetic relationships of the Korean capsid sequence.

This case report presents the first histopathological and molecular detection of CanineCV in South Korea. The findings underscore the importance of genomic surveillance of emerging pathogens and highlight the potential role of CanineCV as a co-infecting agent in canine gastrointestinal diseases. Further studies are required to elucidate the pathogenic mechanisms, epidemiological distribution, and clinical significance of CanineCV, to facilitate the development of preventive and therapeutic strategies. Clinicians should be aware that CanineCV could be a differential diagnosis in dogs with hemorrhagic diarrhea in South Korea.