Effects of duck circovirus on immune function and secondary infection of Avian Pathogenic Escherichia coli

Characterization of an Emerging Recombinant Duck Circovirus in Northern Vietnam, 2023-2024

This study aimed to characterize the duck circovirus circulating in Northern Vietnam based on complete genome sequences. Between 2023 and 2025, 45 pooled tissue samples were collected from nine duck flocks in several provinces in Northern Vietnam. Of the 45 samples tested, 16 (35.56%) were positive for the DuCV genome, as determined using conventional polymerase chain reaction. Nine representative strains were selected for viral genome sequencing. The results indicated that the complete Vietnamese DuCV genomes were from 1992 to 1995 bp in length, and the degree of nucleotide identity shared among them ranged from 96.88% to 99.84%. Phylogenetic analysis of the complete genomes showed that the nine Vietnamese DuCV strains belonged to genotype I, subgenotypes Ia (two strains), Ib (four strains), and Ic (three strains). These viral strains were genetically related to viruses reported in China from 2019 to 2023. Recombination events occurred on the Cap gene sequences of three Vietnamese DuCV strains (Vietnam/VNUA-102/2023, Vietnam/VNUA-225/2023, and Vietnam/VNUA-318/2024). One positive selection was detected on the Rep protein sequence.

Epidemiological investigation and analysis of the genetic evolution of duck circovirus in China, 2022

Duck circovirus (DuCV) infection is an immunosuppressive disease that affects ducks and causes severe damage to their immune system. To elucidate the epidemiological characteristics of DuCV infection in China, a total of 2944 waterfowl samples were collected from 17 provinces from January to October 2022, and 612 DuCV-positive samples were identified. A descriptive statistical analysis was subsequently conducted. Furthermore, 51 near-full-length DuCV genome sequences were obtained, and molecular genetic evolution and recombinant analyses were performed. Geographically, Fujian Province had the highest rate of DuCV positivity (54.8%), followed by the Guangxi Zhuang Autonomous Region (30.4%). The rate of DuCV positivity was highest in samples from 21-40-day-old ducklings, accounting for 66.5% of the total positive samples. The most common pathogen involved in mixed infections with DuCV was parvovirus or Riemerella anatipestifer. Genetic and evolutionary analyses of the full genome sequences of 51 DuCV strains revealed that DuCV-1b and DuCV-2c were the most prevalent strains in China. Genetic recombination analysis suggested that the major parental sequences involved in the recombination of DuCV strains in ducks are present in Anhui, Sichuan, Shandong, and Guangxi. In addition, DuCV recombination events have occurred between strains with different genotypes or strains isolated from different countries. In summary, the DuCV epidemic in China is complex. There are two main co-circulating genotypes, those of the DuCV-1b and DuCV-2c strains, and coinfection of DuCV with other pathogens is a very common phenomenon in clinical practice. There is an urgent demand for vaccines against DuCV, and the protective efficacy of these vaccines against different DuCV genotypes needs to be carefully evaluated.

Study on the infection characteristics and pathogenesis of duck circovirus 1 in Cherry Valley meat ducks

Duck circovirus (DuCV) infected multiple breeds of ducks and was widespread in duck factories worldwide. Infected ducks exhibited feathering disorder, growth retardation and immunosuppression, which lead to secondary infection with other pathogens easily. But till now, there has been little research on the study of DuCV due to the absence of appropriate cultural measures. This study developed an animal model to investigate the pathogenesis of DuCV-1 in vivo by infecting 84 one-day-old Cherry Valley meat ducklings. At 1, 3, 7, 14, 21, 28 and 35 days post-infection (DPI), six Cherry Valley meat ducks were randomly chosen to detect some indexes. The results showed that ducks infected with DuCV-1 exhibited depression, feather disorders and gained weight slowly. DuCV-1 was detected in serum, cloacal swabs, and throat swabs at 1 DPI and sustained during the experimental period. The contents of calcium, phosphorus and lymphocytes decreased while alanine aminotransferase and total bilirubin increased in the serum of sick ducks. DuCV-1 was detectable in all organs and caused multiple local lesions. The virus was initially detected in the liver and the organ with the highest viral titer was the thymus. Besides, immune organ indexes were significantly decreased. These results demonstrated that DuCV-1 could be transmitted horizontally and cause infection persistently. It possesses broad tissue tropism, damaging immune organs and potentially inducing immune suppression. This study could provide references for future research on the pathogenic mechanism of DuCV.

CRISPR/Cas12a and recombinase polymerase amplification-based rapid on-site nucleic acid detection of duck circovirus

BACKGROUND

Duck circovirus (DuCV) infections commonly induce immunosuppression and secondary infections in ducks, resulting in significant economic losses in the duck breeding industry. Currently, effective vaccines and treatments for DuCV have been lacking. Therefore, rapid, specific, and sensitive detection methods are crucial for preventing and controlling DuCV.

METHODS

A lateral flow strip (LFS) detection method was developed using recombinase polymerase amplification (RPA) and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 12a (Cas12a). The RPA-CRISPR/Cas12a-LFS targeted the DuCV replication protein (Rep) and was operated at 37 ℃ and allowed for visual interpretation without requiring sophisticated equipment.

RESULTS

The results revealed that the reaction time of RPA-CRISPR/Cas12a-LFS is only 45 min. This method achieved a low detection limit of 2.6 gene copies. Importantly, this method demonstrated high specificity and no cross-reactivity with six other avian viruses. In a study involving 97 waterfowl samples, the Rep RPA-CRISPR/Cas12a-LFS showed 100% consistency and agreement with real-time quantitative polymerase chain reaction.

CONCLUSION

These findings underscored the potential of this user-friendly, rapid, sensitive, and accurate detection method for on-site DuCV detection.

Epidemiological Investigation and Genetic Analysis of Duck Circovirus in Korea from 2013 to 2022

Duck circovirus (DuCV) infections cause immunosuppression in ducks, potentially leading to significant economic losses for the duck farming industry. This study investigates the prevalence, genetic characteristics, and evolutionary trends of DuCV in Korea between 2013 and 2022. Samples from 184 farms across seven provinces were analyzed using polymerase chain reaction (PCR). The overall DuCV infection rate was 29.4% (54/184), with Jeollanam-do showing the highest prevalence (37.5%, 15/40). Ducks aged 3-6 weeks were most susceptible to infection, while ducklings younger than one week were rarely infected. Whole-genome sequencing was performed on 24 positive samples with phylogenetic analysis revealing that DuCV-1b is the predominant subtype in Korea (23/24 strains). Notably, a Korean DuCV-1a subtype strain was identified for the first time, showing close genetic relatedness to Chinese DuCV 1a strains. Novel subtype-specific amino acid variations in ORF1 and ORF2 were statistically analyzed and classified. Recombination analysis suggested some Korean DuCV-1b strains may have resulted from recombination events involving strains from different countries. This comprehensive study provides crucial insights into the current prevalence, genetic diversity, and evolutionary dynamics of DuCV in Korea, offering valuable data for developing effective control strategies and understanding the global epidemiology of this economically important avian pathogen.

High Prevalence of a Novel Circovirus in the European Hedgehog (Erinaceus europaeus), a Common Species in Decline

Hedgehog (Erinaceus europaeus) declines in western Europe have been associated with the emergence of Hedgehog diphtheric disease (HDD), with a probable multifactorial, yet unidentified etiology. We used metagenomic sequencing of cell-free DNA (cfDNA) in hedgehog blood to identify possible causes of HDD. We detected a novel circovirus species in the European hedgehog, providing the first record of a circovirus within the mammalian order Eulipotyphla. The novel circovirus genome exhibits the characteristic circovirus structure, including a functional replicase (REP) and capsid (CAP) gene. Phylogenetic analysis placed all four detected genomes in a monophyletic clade, most closely related to sequences isolated from dogs. Subsequent PCR-based screening of 188 hedgehog liver samples demonstrated a high prevalence (61%) of this circovirus in hedgehogs brought to wildlife rescue centers, however, without any significant association with HDD. Since circoviruses are well known to interfere with host immunity across mammalian and avian taxa, the high level of circovirus detection in hedgehogs warrants further research into the role of this novel virus in hedgehog health.

Duck circovirus regulates the expression of duck CLDN2 protein by activating the MAPK-ERK pathway to affect its adhesion and infection

Duck circovirus (DuCV) is widely recognized as a prominent virus in China's duck farming industry, known for its ability to cause persistent infections and significant immunosuppression, which can lead to an increased susceptibility to secondary infections, posing a significant threat to the duck industry. Moreover, clinical evidence also indicates the potential vertical transmission of the virus through duck embryos to subsequent generations of ducklings. However, the limited availability of suitable cell lines for in vitro cultivation of DuCV has hindered further investigation into the molecular mechanisms underlying its infection and pathogenicity. In this study, we observed that oral DuCV infection in female breeding ducks can lead to oviduct, ovarian, and follicular infections. Subsequently, the infection can be transmitted to the fertilized eggs, resulting in the emergence of virus-carrying ducklings upon hatching. In contrast, the reproductive organs of male breeding ducks were unaffected by the virus, thus confirming that vertical transmission of DuCV primarily occurs through infection in female breeding ducks. By analyzing transcriptome sequencing data from the oviduct, we focused on claudin-2, a gene encoding the tight junction protein CLDN2 located on the cell membrane, which showed significantly increased expression in DuCV-infected oviducts of female breeding ducks. Notably, CLDN2 was confirmed to interact with the unique structural protein of DuCV, namely capsid protein (Cap), through a series of experimental approaches including co-immunoprecipitation (co-IP), GST pull-down, immunofluorescence, and adhesion-blocking assays. Furthermore, we demonstrated that the Cap protein binds to the extracellular loop structural domains EL1 and EL2 of CLDN2. Subsequently, by constructing a series of truncated bodies of the CLDN2 promoter region, we identified the transcription factor SP5 for CLDN2. Moreover, we found that DuCV infection triggers the activation of the MAPK-ERK signaling pathway in DEF cells and ducks, leading to an upregulation of SP5 and CLDN2 expression. This process ultimately leads to the transportation of mature CLDN2 to the cell surface, thereby facilitating increased virus adherence to the target organs. In conclusion, we discovered that DuCV utilizes host CLDN2 proteins to enhance adhesion and infection in oviducts and other target organs. Furthermore, we elucidated the signaling pathways involved in the interaction between DuCV Cap proteins and CLDN2, which provides valuable insights into the molecular mechanism underlying DuCV's infection and vertical transmission.

IMPORTANCE

Although duck circovirus (DuCV) poses a widespread infection and a serious hazard to the duck industry, the molecular mechanisms underlying DuCV infection and transmission remain elusive. We initially demonstrated vertical transmission of DuCV through female breeding ducks by simulating natural infection. Furthermore, a differentially expressed membrane protein CLDN2 was identified on the DuCV-infected oviduct of female ducks, and its extracellular loop structural domains EL1 and EL2 were identified as the interaction sites of DuCV Cap proteins. Moreover, the binding of DuCV Cap to CLDN2 triggered the intracellular MAPK-ERK pathway and activated the downstream transcription factor SP5. Importantly, we demonstrated that intracellular Cap also interacts with SP5, leading to upregulation of CLDN2 transcription and facilitating enhanced adherence of DuCV to target tissue, thereby promoting viral infection and transmission. Our study sheds light on the molecular mechanisms underlying vertical transmission of DuCV, highlighting CLDN2 as a promising target for drug development against DuCV infection.

Molecular genotyping and subgenotyping of duck circovirus at duck farms in Thailand

Background and Aim

Ducks worldwide are infected with duck circovirus (DuCV), which causes feather abnormality, emaciation, and poor growth performance. DuCV is similar to other circoviruses that induce immunosuppression due to the occurrence of the bursae of Fabricius (BF) and spleen atrophies. In Thailand, retarded ducks with feather losses were submitted for disease investigation. The ducks presented low body weight gain, had small BF and spleens, and were consistent with duck-infected DuCV. Our study investigated the possibility of DuCV infection in duck flocks in Thailand. We also analyzed the genetic characteristics of the virus.

Materials and Methods

BF and spleen samples were collected from affected meat and layer ducks from six farms thought to have been infected with DuCV. These tissues were then subjected to histopathological examination and molecular identification using conventional polymerase chain reaction and nucleotide sequencing. To identify DuCV, phylogenetic trees were generated using MEGA version X software. Samples of tissues or swabs were collected to determine whether coinfections with bacteria and viruses existed.

Results

Phylogenetic analysis using the entire genome (1995-1996 bp) and cap gene (762 bp) revealed that the DuCV isolates circulating in Thailand belonged to DuCV genotype I, which was further subdivided into two sub-genotypes: sub-genotype I b and an unclassified sub-genotype based on reference sub-genotypes. Thai isolates have variations in 10 amino acid residues in the capsid protein. Ducks infected with Thai DuCV were also coinfected with Riemerella anatipestifer, Escherichia coli, Pasteurella multocida, duck viral enteritis, and duck Tembusu virus, which is consistent with previous DuCV infection studies.

Conclusion

Six DuCVs from ducks who were previously found to have feather loss, were underweight, had growth retardation, and had poor body condition were identified in this study as belonging to genotype I and constituting at least two sub-genotypes. Due to the immunosuppressive effects of DuCV, coinfection of bacterial and viral pathogens was typically observed in Thai DuCV-infected ducks.

Feeding live yeast (Saccharomyces cerevisiae) improved performance of mid-lactation dairy cows by altering ruminal bacterial communities and functions of serum antioxidation and immune responses

BACKGROUND

The utilization of live yeast (Saccharomyces cerevisiae, YE) in dairy cows is gaining traction in dairy production as a potential strategy to improve feed efficiency and milk yield. However, the effects of YE on dairy cow performance remain inconsistent across studies, leaving the underlying mechanisms unclear. Hence, the primary aim of this study was to investigate the impact of YE supplementation on lactation performance, ruminal microbiota composition and fermentation patterns, as well as serum antioxidant capacity and immune functions in dairy cows.

RESULTS

Supplementation with YE (20 g/d/head) resulted in enhancements in dairy cow's dry matter intake (DMI) (P = 0.016), as well as increased yields of milk (P = 0.002) and its components, including solids (P = 0.003), fat (P = 0.014), protein (P = 0.002), and lactose (P = 0.001) yields. The addition of YE led to significant increases in the concentrations of ammonia nitrogen (NH3-N) (P = 0.023), acetate (P = 0.005), propionate (P = 0.025), valerate (P = 0.003), and total volatile fatty acids (VFAs) (P < 0.001) in rumen fermentation parameters. The analysis of 16s rRNA gene sequencing data revealed that the administration of YE resulted in a rise in the relative abundances of three primary genera including Ruminococcus_2 (P = 0.010), Rikenellaceae_RC9_gut_group (P = 0.009), and Ruminococcaceae_NK4A214_group (P = 0.054) at the genus level. Furthermore, this increase was accompanied with an enriched pathway related to amino acid metabolism. Additionally, enhanced serum antioxidative (P < 0.05) and immune functionalities (P < 0.05) were also observed in the YE group.

CONCLUSIONS

In addition to improving milk performance, YE supplementation also induced changes in ruminal bacterial community composition and fermentation, while enhancing serum antioxidative and immunological responses during the mid-lactation stage. These findings suggest that YE may exert beneficial effects on both rumen and blood metabolism in mid-lactation dairy cows.

From obscurity to urgency: a comprehensive analysis of the rising threat of duck circovirus

Duck circovirus (DuCV) is a small, nonenveloped, single-stranded DNA virus with immunosuppressive effects on ducks that leads to slow growth and elevated mortality following mixed infections. Its infection manifests as feather loss, slow growth, swelling of respiratory tissue, and damage to immune organs in ducks. Although single infections with DuCV do not cause noticeable clinical symptoms, its ability to compromise the immune system and facilitate infections caused by other pathogens poses a serious threat to duck farming. Given the prevalence of this disease and the increasing infection rates in recent years, which have resulted in significant economic losses in duck farming and related sectors, research and control of DuCV infection have become especially important. The aim of this review is to provide a summary of the current understanding of DuCV, serving as a reference for subsequent research and effective control of the virus. We focus mainly on the genetics and molecular biology, epidemiology, clinical symptoms, and pathology of DuCV. Additionally, topics such as the isolation and culture of the virus, vaccines and antiviral therapies, diagnostics, and preventative measures are discussed.

Molecular Detection and Genetic Characterization of Vertically Transmitted Viruses in Ducks

To investigate the distribution and genetic variation in four vertically transmitted duck pathogens, including duck hepatitis B virus (DHBV), duck circovirus (DuCV), duck hepatitis A virus 3 (DHAV-3), and avian reoviruses (ARV), we conducted an epidemiology study using PCR and RT-PCR assays on a duck population. We found that DHBV was the most prevalent virus (69.74%), followed by DuCV (39.48%), and then ARV (19.92%) and DHAV-3 (8.49%). Among the 271 duck samples, two, three or four viruses were detected in the same samples, indicating that the coinfection of vertical transmission agents is common in ducks. The genetic analysis results showed that all four identified DuCV strains belonged to genotype 1, the DHAV-3 strain was closely clustered with previously identified strains from China, and the ARV stain was clustered under genotype 1. These indicate that different viral strains are circulating among the ducks. Our findings will improve the knowledge of the evolution of DuCV, DHAV-3, and ARV, and help choose suitable strains for vaccination.

Development and application of a multiplex qPCR assay for the detection of duck circovirus, duck Tembusu virus, Muscovy duck reovirus, and new duck reovirus

A multiplex qPCR assay was developed to simultaneously detect duck circovirus (DuCV), duck Tembusu virus (DTMUV), Muscovy duck reovirus (MDRV), and novel duck reovirus (NDRV), but it did not amplify other viruses, including duck virus enteritis (DVE), infectious bursal disease virus (IBDV), avian reovirus (ARV), H5 avian influenza virus (H5 AIV), H7 avian influenza virus (H7 AIV), H9 avian influenza virus (H9 AIV), Newcastle disease virus (NDV), and Muscovy duck parvovirus (MDPV), and the detection limit for DuCV, DTMUV, MDRV, and NDRV was 1.51 × 10¹ copies/μL. The intra- and interassay coefficients of variation were less than 1.54% in the repeatability test with standard plasmid concentrations of 1.51 × 10⁷, 1.51 × 10⁵, and 1.51 × 10³ copies/μL. The developed multiple qPCR assay was used to examine 404 clinical samples to verify its practicability. The positivity rates for DuCV, DTMUV, MDRV, and NDRV were 26.0%, 9.9%, 4.0%, and 4.7%, respectively, and the mixed infection rates for DuCV + DTMUV, DuCV + MDRV, DuCV + NDRV, MDRV + NDRV, DTMUV + MDRV, and DTMUV + NDRV were 2.7%, 1.2%, 1.2%, 1.0%, 0.5%, and 0.7%, respectively.

Evaluation of the antiviral effect of four plant polysaccharides against duck circovirus

Recently, outbreaks of duck circovirus (DuCV) are frequently occurring worldwide due to secondary infections caused by post infection-induced immunosuppression. Due to a lack of preventive drugs and vaccines, the waterfowl industry losses are ever increasing. In this study, we extracted Astragalus polysaccharides (APS), pine pollen polysaccharides (PPPS), Aloe vera polysaccharides (AVE), and Ficus carica polysaccharides (FCPS) from Astragalus, pine pollen, aloe, and F. carica leaves, respectively. We randomly divided 150 one-day-old Cherry Valley ducks into five groups, which were inoculated with the DuCV solution and orally administered APS, PPPS, AVE, FCPS, and phosphate buffer saline (PBS), respectively. We collected the duck immune organs and serum samples at 8, 16, 24, 32, 40, and 48 days post-infection (dpi). Using clinical symptom analysis, molecular biology experiments, and serological experiments, we proved that plant polysaccharides could (a) improve the duck immunity, (b) reduce the viral load, and (c) mitigate DuCV-induced damage to immune organs, with both APS and PPPS having significant effects. Moreover, we detected viral load and cytokines within the first 8 dpi. Since the body's innate immunity could inhibit viral replication within five days of virus infection, 1-5 dpi was the best treatment time. Among the four polysaccharides showing in vitro anti-apoptotic activity, APS and PPPS significantly inhibited the DuCV infection-induced apoptosis of peripheral blood lymphocytes. Overall, since our findings show APS and PPPS having significant anti-DuCV effects both in vivo and in vitro, they can be promising candidates for preventing DuCV infection in ducks.

Canine Circovirus Suppresses the Type I Interferon Response and Protein Expression but Promotes CPV-2 Replication

Canine circovirus (CanineCV) is an emerging virus in canines. Since the first strain of CanineCV was reported in 2012, CanineCV infection has shown a trend toward becoming a global epidemic. CanineCV infection often occurs with coinfection with other pathogens that may aggravate the symptoms of disease in affected dogs. Currently, CanineCV has not been successfully isolated by laboratories, resulting in a lack of clarity regarding its physicochemical properties, replication process, and pathogenic characteristics. To address this knowledge gap, the following results were obtained in this study. First, a CanineCV strain was rescued in F81 cells using infectious clone plasmids. Second, the Rep protein produced by the viral packaging rescue process was found to be associated with cytopathic effects. Additionally, the Rep protein and CanineCV inhibited the activation of the type I interferon (IFN-I) promoter, blocking subsequent expression of interferon-stimulated genes (ISGs). Furthermore, Rep was found to broadly inhibit host protein expression. We speculate that in CanineCV and canine parvovirus type 2 (CPV-2) coinfection cases, CanineCV promotes CPV-2 replication by inducing immunosuppression, which may increase the severity of clinical symptoms.

Novel Circoviruses from Birds Share Common Evolutionary Roots with Fish Origin Circoviruses

Circoviruses occur in a variety of animal species and are common pathogens of mammalian and avian hosts. In our study internal organ samples of wild birds were processed for screening of circoviral sequences. Two novel viruses were identified and characterized in specimens of a little bittern and a European bee-eater that suffered from wing injuries, were weakened, had liver or kidney failures, and finally succumbed at a rescue station. The 1935 nt and 1960 nt long viral DNA genomes exhibited a genomic structure typical for circoviruses and were predicted to encode replication-associated protein in the viral strand, and a capsid protein in the complementary strand of the replicative intermediate DNA form. The genome of the newly described viruses showed 37.6% pairwise identity with each other and ≤41.5% identity with circovirus sequences, and shared a common branch with fish, human and Weddel seal circoviruses in the phylogenetic tree, implying evolutionary relationship among the ancestors of these viruses. Based on the results the little bittern and European bee-eater circoviruses represent two distinct species of the Circovirus genus, Circoviridae family.