Detection of virus particles resembling circovirus and porcine circovirus 2a (PCV2a) sequences in feces of dogs

Recombinant expression and characterization of Canine circovirus capsid protein for diagnosis

Canine circovirus (CanineCV) is a contagious virus that causes severe gastroenteritis, diarrhea, respiratory disease, and vasculitis, often resulting in fatality among infected dogs. In this study, a recombinant Capsid protein (rCap) of CanineCV was expressed in the Escherichia coli (E. coli) Rosetta (DE3) pLysS host cell, followed by affinity purification, and then analyzed by SDS-PAGE, revealing a molecular weight of approximately 31 kDa. The antigenicity of the CanineCV rCap protein was confirmed through recognition by a rabbit anti-CanineCV rCap protein polyclonal antibody (PoAb). Additionally, the reactivity and specificity of this PoAb were assessed using indirect enzyme-linked immunosorbent assay (ELISA) and Western blot analysis before applying in an immunohistochemistry (IHC), namely, immunoperoxidase detection. The immunoperoxidase assay using rabbit anti-CanineCV rCap protein PoAb demonstrated that the CanineCV Cap protein was predominantly located in immune cells, especially lymphocytes and macrophages, within the spleen, lung, tracheobronchial lymph nodes, small intestine, and kidney. Similarly, the Cap protein was also found in pneumocytes in the lung and renal tubular epithelial cells in the kidney. These findings reflected the biological activity and cell tropism of the virus. Therefore, the recombinant Cap protein and its PoAb could be used for the development of a valuable diagnostic tool for CanineCV detection.

First report on identification and genomic analysis of a novel porcine circovirus (porcine circovirus 4) in cats

Porcine circovirus type 4 (PCV4) is an emerging circovirus, which has been detected in domestic pigs across various provinces in China and Korea. In this study, we aimed to investigate whether cats are susceptible to PCV4. For this purpose, we collected 116 cat samples from animal hospitals in Sichuan Province, China, between 2021 and 2022. Using a SYBR Green-based real-time PCR assay, we detected PCV4 in 5 out of the 116 clinical samples, indicating a positive rate of 4.31% (5/116) and confirming the presence of PCV4 in cats from Sichuan Province, China. Moreover, we successfully sequenced and analyzed the complete genome of one PCV4 strain (SCGA-Cat) along with 60 reference sequences deposited in the GenBank database. SCGA-Cat exhibited high nucleotide homology (98.2-99.0%) with PCV4 strains from other species, including dogs, pigs, dairy cows, and fur animals. Notably, the SCGA-Cat strain from cats clustered closely with a PCV4 strain derived from a pig collected in Fujian Province, China. To the best of our knowledge, this study represents the first report on the molecular detection of PCV4 in cats worldwide, which prompted us to understand the genetic diversity and cross-species transmission of the ongoing PCV4 cases. However, further investigations are needed to explore the association between PCV4 infection and clinical syndromes in cats.

Virome of wild rats (Rattus norvegicus) captured far from pig farms in Jiangsu province of China reveals novel porcine circovirus type 2d (PCV2d) sequences

BACKGROUND

Porcine circovirus type 2 (PCV2) has caused great economic losses in the global pig industry. There have been published records of wild rats acting as the reservoirs of PCV2 (only PCV2a and PCV2b), but almost all of which were related to the PCV2-infected swine herds.

RESULTS

In this study, we carried out the detection, amplification, and characterization of novel PCV2 strains in wild rats that were captured far from pig farms. Nested PCR assay demonstrated that the kidney, heart, lung, liver, pancreas, and large and small intestines of rats were screened positive for PCV2. We subsequently sequenced two full genomes of PCV2 in positive sample pools, designated as js2021-Rt001 and js2021-Rt002. Genome sequence analysis indicated that they had the highest similarity to nucleotide sequences of porcine-origin PCV2 isolates in Vietnam. Phylogenetically, js2021-Rt001 and js2021-Rt002 were a part of the PCV2d genotype cluster, which is a predominant genotype circulating worldwide in recent years. The antibody recognition regions, immunodominant decoy epitope, and heparin sulfate binding motif of the two complete genome sequences coincided with those previously reported.

CONCLUSIONS

Our research reported the genomic characterization of two novel PCV2 strains (js2021-Rt001 and js2021-Rt002) and provided the first supported evidence that PCV2d could naturally infect wild rats in China. However, whether the newly identified strains have potential for circulating in nature in vertical and horizontal transmission or inter-species jumping between rats and pigs needs further research.

Canine circovirus: An emerging or an endemic undiagnosed enteritis virus?

Canine Circovirus (CanineCV) belongs to the family Circoviridae. It is an emerging virus described for the first time in 2011; since then, it has been detected in different countries and can be defined as worldwide distribution virus. CanineCV infects domestic and wild canids and is mainly related to hemorrhagic enteritis in canines. However, it has been identified in fecal samples from apparently healthy animals, where in most cases it is found in coinfection with other viral agents such as the canine parvovirus type-2 (CPV). The estimated prevalence/frequency of CanineCV has been variable in the populations and countries where it has been evaluated, reaching from 1 to 30%, and there are still many concepts to define the epidemiological characteristics of the virus. The molecular characterization and phylo-evolutive analyses that allow to postulate the wild origin and intercontinental distribution of the virus. This review focuses on the importance on continuing research and establish surveillance systems for this emerging virus.

The first dog-origin porcine circovirus type 4 complete genomic sequence have high homology with that of pig-derived strains

Introduction: Porcine circovirus 4 (PCV4) was discovered in 2019 and then proved to be pathogenic to piglets. Nevertheless, few studies were currently available about PCV4 infection in species other than pigs and there is no information about the prevalence of PCV4 in dogs. Methods: To fill this gap, 264 dog samples were collected from animal hospitals in the Southwest of China from 2021 to 2022 and screened for PCV4. Moreover, the complete genome of one PCV4 strain (SCABTC-Dog2022) were obtained successfully and shared a high identity (97.9-99.0%) with other PCV4 strains derived from pigs, dairy cows, raccoon dogs and foxes. The SCABTC-Dog2022 were analyzed together with 51 reference sequences. Results and Discussion: The detected results showed a low percentage of PCV-4 DNA (1.14%, 3/264), indicating that PCV4 could be identified in dogs in southwest China. Phylogenetic tree showed that SCABTC-Dog2022 strain derived from dog were clustered in a closed relative and geographically coherent branch with other PCV4 strains collected from four provinces (Sichuan, Fujian, Hunan and Inner Mongolia) of China. To our knowledge, it is the first detection of PCV4 in dogs globally. The association between PCV4 status and clinical syndromes in dogs deserves additional investigations.

First detection and full genomic analysis of Canine Circovirus in CPV-2 infected dogs in Colombia, South America

Canine Circovirus (CanineCV) is an emerging virus which since its first report in USA in 2012, it has been described worldwide. It was the second mammalian circovirus species identified in dogs and its role in canine enteritis is still being uncertain as much as its association in disease with the Canine Parvovirus-2 (CPV-2). Here, we aim to confirm for the first time the presence of CanineCV in Colombia and to develop phylogenetic evolutive analyses of CanineCV in CPV-2 positive animals. DNA from samples were extracted and PCR, full genome sequencing and phylogenetic analysis was performed to detect and characterize CanineCV. From a total of 30 CPV-2 positive samples, 16.6% (n = 5) were positives for CanineCV. Sequencing analysis of Colombian CanineCV wild-type strains displayed high identity to each other (99.5–99.7% nt; 99.7% aa). The full genome phylogenetic analysis confirmed that worldwide reported CanineCV strains were separated into four distinct genotypes in addition to a European origin of the South American CanineCV strains. This study demonstrated the importance of continue surveillance of emerging viruses in canine populations and confirm for the first time the circulation and origin of CanineCV in Colombia.

Porcine circoviruses: current status, knowledge gaps and challenges

Circoviruses (CV) include some of the smallest viruses known. They were named after their circularly arranged single-stranded DNA genome with a gene encoding a conserved replicase protein on the sense strand. Circoviruses are widely distributed in mammals, fish, avian species and even insects. In pigs, four different CVs have been identified and named with consecutive numbers based on the order of their discovery: Porcine circovirus 1 (PCV1), Porcine circovirus 2 (PCV2), Porcine circovirus 3 (PCV3) and most recently Porcine circovirus 4 (PCV4). PCVs are ubiquitous in global pig populations and uninfected herds are rarely found. It is generally accepted that PCV1 is non-pathogenic. In contrast, PCV2 is considered an important, economically challenging pathogen on a global scale with comprehensive vaccination schemes in place. The role of PCV3 is still controversial several years after its discovery. Propagation of PCV3 appears to be challenging and only one successful experimental infection model has been published to date. Similarly to PCV2, PCV3 is widespread and found in many pigs regardless of their health history, including high health herds. PCV4 has only recently been discovered and further information on this virus is required to understand its potential impact. This review summarizes current knowledge on CVs in pigs and aims to contrast and compare known facts on PCVs.

Detection of Antibodies Against Canine Circovirus in Naturally and Experimentally Infected Canines by Recombinant Capsid Enzyme-Linked Immunosorbent Assay

Canine circovirus (CanineCV), a new pathogen, was found to be associated with canine hemorrhagic diarrhea, vasculitis, granulomatous lymphadenitis, and acute gastroenteritis. Although CanineCV was highly positive rate in diarrhea cases, its pathogenicity remains controversial. In this study, the seroprevalence and associated risk factors of CanineCV infection among domestic dogs in northeastern China was investigated by an indirect enzyme-linked immunosorbent assay (iELISA) based on recombinant capsid protein. Results revealed the proposed iELISA had no cross-reactivity with other related pathogens, and yielded good diagnostic values. Then, to evaluate the rCap iELISA, this study applied it to detect antibodies against CanineCV in 1,047 clinical serum samples obtained from northeastern China in 2016–2017. Results showed the positive rates in the five cities of Jilin, Liaoning, and Heilongjiang provinces ranged from 22.22 to 42.29%. Statistical analysis shows a significant difference in age between dogs <3 months old with respect to the >1-year-old dogs (p = 0.005), that is, the CanineCV infection was more frequently identified from older dogs. In the artificially infected experiment, the dogs developed seroconversion after 9 or 12 days and the main way of virus excretion was through feces. More interestingly, among the 32 ELISA-positive serum samples, 34.75% samples tested positive for the CanineCV DNA by qPCR, far higher than that in ELISA-negative serum samples (5.26%, 2/38). This report is the first to demonstrate that CanineCV infection is common in the dog population in northeastern China. The results showed obvious differences in the positive rate associated with diarrhea, age, but not with different cities. This study also provide basis for evaluating the pathogenic potential of CanineCV. But, the pathogenicity, the relationship between antibody level and immune protection, and the harmful effects of this virus remain to be established.

Genomic characterization of a novel circovirus from a stranded Longman's beaked whale (Indopacetus pacificus)

Tissues from a juvenile Longman's beaked whale that stranded in Hawaii in 2010 were screened for viruses using a Next-Generation Sequencing (NGS) approach. From the NGS data, the full genome (1,849 bp) of a novel beaked whale circovirus (BWCV) was determined. Two open reading frames (ORF) were annotated, including ORF1 that encodes the capsid gene, ORF2 that encodes the replication-associated gene, and a 9-bp conserved nonamer on the apex of the open loop found in all circoviruses. Independent phylogenetic analyses based on amino acid sequence alignments of the two CV proteins supported the BWCV as a member of the genus Circovirus, branching as the sister species to the recently discovered canine circovirus. A sequence identity matrix generated from complete genome alignments revealed the BWCV displays between from 51.1 to 56.7% nucleotide identity to other circoviruses, which is lower than the 80% threshold proposed for species demarcation. Considering the genetic and phylogenetic analyses, we propose the formal species designation of beaked whale circovirus. An endpoint PCR assay targeting the BWCV genome confirmed the presence of the BWCV DNA in every tissue from which DNA was extracted, including spleen, muscle, left ventricle, left adrenal gland, liver, lung, cerebrum, cerebellum, and lymph node. An automated in situ hybridization assay utilizing RNAscope® technology and targeting the replication-associated gene resulted in labeling of individual cells morphologically resembling mononuclear leukocytes and cells of blood vessels in diaphragm, liver, lymph nodes, lung, pericardium, oral mucosa and tongue, adrenal gland, testis, aorta, intestine, stomach and heart. The clinical or pathologic significance of BWCV is undetermined, as are its host range, prevalence, and pathogenicity in cetaceans of Hawaiian waters and elsewhere.

Reservoirs of Porcine Circoviruses: A Mini Review

Porcine circovirus (PCV) is one of the smallest known DNA viruses in mammals. At present, PCVs are divided into three species, PCV1, PCV2, and PCV3. PCV1 and PCV2 were found in the 1970s and the 1990s, respectively, whereas PCV3 was discovered recently in 2016. PCV1 does not cause diseases in pigs. However, PCV3, similar to PCV2, is reported to be associated with several swine diseases, including porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCVs are very common in domestic pigs as well as wild boars. However, PCVs have been occasionally isolated from non-porcine animals, including ruminants (such as cattle, goats, wild chamois, and roe deers), rodents (such as NMRI mice, BALB/c mice, Black C57 mice, ICR mice, Mus musculus, and Rattus rattus), canines (such as dogs, minks, foxes, and raccoon dogs), insects (such as flies, mosquitoes, and ticks), and shellfish. Moreover, PCVs are frequently reported in biological products, including human vaccines, animal vaccines, porcine-derived commercial pepsin products, and many cell lines. PCVs are also abundant in the environment, including water samples and air samples. Interestingly, PCV1 and/or PCV2 antibody or antigen has also been detected in sera, stool samples and respiratory swab samples of human, revealing zoonotic potential of PCVs. Thus, PCVs inhabit many types of reservoirs. In this review, we summarize the reservoirs of PCVs, and this information would be helpful in understanding the natural circulating status and possible cross-species transmission of PCVs.

First detection and phylogenetic analysis of porcine circovirus type 2 in raccoon dogs

Background

Porcine circovirus type 2 (PCV2) is a major emerging virus of porcine circovirus-associated disease (PCVAD), which has brought huge economic losses to the global pig industry. Pigs are well known as the natural reservoir of PCV2. Recently, many researchers have revealed PCV2 could infect many other mammals like mice, calves, minks, dogs and goats. In 2018, our laboratory has admitted six cases of raccoon dogs from Qinhuangdao city of China, which were characterized by inappetence, lethargy, depression, abortion, and sterility.

Results

At last, six raccoon dog-origin PCV2 strains were isolated in this study. Pairwise-sequence comparisons demonstrated that the six raccoon dog-origin PCV2 strains shared a nucleotide similarity of 92.1–99.8% among 40 PCV2 representative strains. Phylogenetic analysis indicated these PCV2 isolates belonged to Chinese epidemic genotypes PCV2b and PCV2d. And aborted or sterile symptom was significantly associated with PCV2 infection in raccoon dogs by the chi-square test (χ² = 87.3, p < 0.001). The retrospective study revealed that raccoon dog-origin PCV2 strains shared 100% sequence similarity with the PCV2 stains isolated from pig farms around these raccoon dog farms, respectively.

Conclusion

In this study, the first supported evidence of PCV2 prevalence in raccoon dog farms of China was documented. PCV2 may be one of the most significant causative agents resulting in the reproductive failure of farmed raccoon dogs, implying that PCV2 could transmit from pigs to raccoon dogs. That indicated that PCV2 cross-species transmission will be a serious threat to China’s fur animal farming industry.

First detection and genetic analysis of fox-origin porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is a causative agent of porcine circovirus-associated disease (PCVAD), which is a serious problem in the swine industry worldwide. In recent years, nonporcine-origin PCV2 has attracted more and more attention of the researchers. This study reported on the first identification of PCV2 in farmed foxes with reproductive failure. Three fox-origin PCV2 strains were successfully isolated, sequenced, and designated as FoxHB1, FoxHB2, and FoxHB3 respectively. Pairwise-sequence comparisons of the complete genomes revealed that three fox-origin PCV2 strains had nucleotide identities varied from 91.9% to 99.7% with representative strains of PCV2 different genotypes. Meanwhile, phylogenetic analysis based on complete genomes of 44 PCV2 strains indicated that the fox-origin PCV2 strains belonged to Chinese epidemic genotypes PCV2b and PCV2d. These results provided the first supported evidence that PCV2 could infect foxes, implying that the cross-species transmission of PCV2 would be a big threat to Chinese fur animal-bearing industry.