Presence of antibodies reacting with porcine circovirus in sera of humans, mice, and cattle

First Molecular Detection and Genetic Analysis of a Novel Porcine Circovirus (Porcine Circovirus 4) in Dogs in the World

A novel circovirus species was identified in farmed pigs and designated porcine circovirus 4 (PCV4); it has recently been proved to be pathogenic to piglets. However, little is known about its cross-species transmission, and there is no evidence of PCV4 in dogs. A total of 217 fecal samples were collected from diarrheal dogs in Henan Province, China, and tested for the presence of PCV4 using a real-time PCR assay. Among the 217 samples, the total positivity rate for PCV4 was 5.99% (13/217 samples), with rates of 7.44% and 4.17% in 2020 and 2021, respectively. PCV4 was detected in dogs in 6 of 10 cities, demonstrating that PCV4 could be detected in dogs in Henan Province, China. One PCV4 strain (HN-Dog) was sequenced in this study and shared high levels of identity (97.9% to 99.6%) with reference strains at the genome level. Phylogenetic analysis based on complete genome sequences of HN-Dog and 42 reference strains showed that the HN-Dog strain was closely related to 3 PCV4 reference strains (from pig, raccoon dog, and fox) but differed genetically from other viruses in the genus Circovirus. Three genotypes, i.e., PCV4a, PCV4b, and PCV4c, were confirmed by phylogenetic analysis of complete genome sequences of 42 PCV4 strains, and one amino acid variation in Rep protein (V239L) and three amino acid variations in Cap protein (N27S, R28G, and M212L) were considered conserved genotype-specific molecular markers. In conclusion, the present study is the first to report the discovery of the PCV4 genome in dogs, and the association between PCV4 infection and diarrhea warrants further study. IMPORTANCE This study is the first to report the presence of PCV4 in dogs worldwide, and the first complete genome sequence was obtained from a dog affected with diarrhea. Three genotypes of PCV4 strains (PCV4a, PCV4b, and PCV4c) were determined, as supported by specific amino acid markers (V239L for open reading frame 1 [ORF1] and N27S R28G and M212L for ORF2). These findings help us understand the current status of intestinal infections in pet dogs in Henan Province, China, and also prompted us to accelerate research on the pathogenesis, epidemiology, and cross-species transmission of PCV4.

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 complete genome analysis of porcine circovirus-like virus P1 and porcine circovirus-2 in yak in China

Porcine circovirus-like virus P1, like porcine circovirus type 2 (PCV2), is a potential pathogen of post-weaning multisystemic wasting syndrome in swine. Yaks are a valuable species and an iconic symbol of the Tibet Plateau which is the highest and largest plateau in the world. In this study, a total of 105 yak diarrheal samples, collected from 13 farms in Linzhi in the Tibet Plateau from January 2019 to December 2021, that were screened for P1 and PCV2 by polymerase chain reaction, 10.48% (n = 11) were positive for P1, 4.76% (n = 5) for PCV2, and 5.71% (n = 6) were positive for coinfection of P1 and PCV2. In addition, the whole genomes of eight P1 strains and eight PCV2 strains were sequenced. Alignment of deduced amino acid sequences of P1 ORF1 and PCV2 ORF2 gene revealed that ON012566 had one unique amino acid mutation at residues 137 (T to P). This mutation has important implication for the study of virus virulence, tissue tropism, and immune response. Phylogenetic analysis shows that the yak-origin P1 strains in this study with cattle-origin P1 reference strains were grouped into one cluster. The yak-origin PCV2 (ON012566) and a buffalo-origin PCV2 (KM116514) reference strain clustered in the same branch in the PCV2b regions. Meanwhile, the remaining PCV2 strains and buffalo-origin PCV2 reference strain (ON012565) clustered in the PCV2d regions. To summarize, to our knowledge, this is the first report on the molecular prevalence and genome characteristics of P1 and PCV2 in yaks in the world and will contribute to further study of the molecular epidemiology, source, and evolution of P1 and PCV2 strains.

Cross-species transmission of an emerging porcine circovirus (PCV4): First molecular detection and retrospective investigation in dairy cows

Porcine circovirus 4 (PCV4), a novel porcine circovirus identified in pigs, has recently been proved to be pathogenic to piglets. However, little is known about its cross-species transmission, and demonstration of PCV4 in dairy cows is lacking. To explore whether the PCV4 genome exists in dairy cows, 1170 fecal samples were collected from dairy farms in 7 cities in Henan Province of China during 2012-2021, and screened by qPCR for the presence of PCVs (PCV2-PCV4). The detection results showed that the positive rate of PCV4 in dairy cows was 2.22 % (26/1170), but all fecal samples were negative for PCV2 and PCV3. Three full-length and five partial genomes of PCV4 strains were acquired, of which two PCV4 strains (NY2012-DC and XC2013-DC) were achieved from 2012 and 2013, indicating that PCV4 has been circulating in dairy cows in Henan Province of China for at least 10 years. The three PCV4 strains sequenced in this study shared high identity (97.5-99.5 %) with reference strains at the genome level. In phylogenetic analysis, three genotypes (PCV4a, PCV4b and PCV4c) were temporarily confirmed by analyzing 44 strains, and one amino acid variation in Rep (V239L) and three amino acid variations in Cap (N27S, R28G and M212L) were considered as a conserved genotype specific molecular marker. Analyzed from three perspectives (cross-time, cross-species and transboundary), the high nucleotide homology of PCV4 strains indicated the PCV4 evolutionary rate might be slow. Overall, this study was the first to report the detection of PCV4 in dairy cows and conducted a long-term retrospective investigation of PCV4 in Henan Province of China, which has important implications for understanding the genetic diversity and cross-species transmission of the ongoing PCV4 cases.

Efficient application of a baculovirus-silkworm larvae expression system for obtaining porcine circovirus type 2 virus-like particles for a vaccine

Porcine circovirus type 2 (PCV2) is a major pathogen associated with swine diseases. It is the smallest single-stranded DNA virus, and its genome contains four major open reading frames (ORFs). ORF2 encodes the major structural protein Cap, which can self-assemble into virus-like particles (VLPs) in vitro and contains the primary antigenic determinants. In this study, we developed a high-efficiency method for obtaining VLPs and optimized the purification conditions. In this method, we expressed the protein Cap with a 6× His tag using baculovirus-infected silkworm larvae as well as the E. coli BL21(DE3) prokaryotic expression system. The PCV2 Cap proteins produced by the silkworm larvae and E. coli BL21(DE3) were purified. Cap proteins purified from silkworm larvae self-assembled into VLPs in vitro, while the Cap proteins purified from bacteria were unable to self-assemble. Transmission electron microscopy confirmed the self-assembly of VLPs. The immunogenicity of the VLPs produced using the baculovirus system was demonstrated using an enzyme-linked immunosorbent assay (ELISA). Furthermore, the purification process was optimized. The results demonstrated that the expression system using baculovirus-infected silkworm larvae is a good choice for obtaining VLPs of PCV2 and has potential for the development of a low-cost and efficient vaccine.

Risk Assessment for Use of a Porcine Circovirus-Contaminated Reagent in a Barrier Maintained Rodent Colony

A proposal for the use of porcine pancreatic elastase (PPE) to develop a mouse model of pulmonary emphysema raised concerns about introducing contaminating porcine viruses into our barrier facility. Porcine Circovirus (PCV) is a known contaminant of vaccines and cell cultures that have been exposed to porcine-derived reagents. Endemic infection of PCV3 in laboratory mice has been reported, and some evidence supports natural PCV infection in wild mice. PPE samples from 2 different vendors tested positive for DNA from both PCV2 and 3. To allow model development with these reagents to proceed, we developed a protocol that would meet scientific objectives, minimize exposure of mice, and provide information on the potential for the virus to spread. Five d after BALB/c mice received intralaryngeal administration of PPE, lungs were harvested and analyzed for evidence of disease. Tissues from other major organs were submitted to test for disseminated PCV2 and 3 DNA. Similarly, tissues (including lungs) from direct contact nude sentinel mice were analyzed for the presence of the virus. To evaluate the possibility of endemic PCV2/3 infection, we also surveyed non-porcine reagent exposed mice on other studies. PCV2 and 3 was not detected in any of the tissues submitted. Although this study provided no evidence of infection and transmission of PCV2/3 from the contaminated PPE sample over the 5 d study, further work is needed to understand the risks and impact of introducing PCV contaminated cells or reagents into barrier maintained rodent colonies.

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.

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.

Pathogen elimination and prevention within a regulated, Designated Pathogen Free, closed pig herd for long-term breeding and production of xenotransplantation materials

BACKGROUND

We established a Source Animal (barrier) Facility (SAF) for generating designated pathogen-free (DPF) pigs to serve as donors of viable organs, tissues, or cells for xenotransplantation into clinical patients. This facility was populated with caesarian derived, colostrum deprived (CDCD) piglets, from sows of conventional-specific (or specified) pathogen-free (SPF) health status in six cohorts over a 10-month period. In all cases, CDCD piglets fulfilled DPF status including negativity for porcine circovirus (PCV), a particularly environmentally robust and difficult to inactivate virus which at the time of SAF population was epidemic in the US commercial swine production industry. Two outbreaks of PCV infection were subsequently detected during sentinel testing. The first occurred several weeks after PCV-negative animals were moved under quarantine from the nursery into an animal holding room. The apparent origin of PCV was newly installed stainless steel penning, which was not sufficiently degreased thereby protecting viral particles from disinfection. The second outbreak was apparently transmitted via employee activities in the Caesarian-section suite adjacent to the barrier facility. In both cases, PCV was contained in the animal holding room where it was diagnosed making a complete facility depopulation-repopulation unnecessary.

METHOD

Infectious PCV was eliminated during both outbreaks by the following: euthanizing infected animals, disposing of all removable items from the affected animal holding room, extensive cleaning with detergents and degreasing agents, sterilization of equipment and rooms with chlorine dioxide, vaporized hydrogen peroxide, and potassium peroxymonosulfate, and for the second outbreak also glutaraldehyde/quaternary ammonium. Impact on other barrier animals throughout the process was monitored by frequent PCV diagnostic testing.

RESULT

After close monitoring for 6 months indicating PCV absence from all rooms and animals, herd animals were removed from quarantine status.

CONCLUSION

Ten years after PCV clearance following the second outbreak, due to strict adherence to biosecurity protocols and based on ongoing sentinel diagnostic monitoring (currently monthly), the herd remains DPF including PCV negative.

Surveillance for respiratory and diarrheal pathogens at the human-pig interface in Sarawak, Malaysia

BACKGROUND

The large livestock operations and dense human population of Southeast Asia are considered a hot-spot for emerging viruses.

OBJECTIVES

To determine if the pathogens adenovirus (ADV), coronavirus (CoV), encephalomyocarditis virus (EMCV), enterovirus (EV), influenza A-D (IAV, IBV, ICV, and IDV), porcine circovirus 2 (PCV2), and porcine rotaviruses A and C (RVA and RVC), are aerosolized at the animal-interface, and if humans working in these environments are carrying these viruses in their nasal airways.

STUDY

This cross-sectional study took place in Sarawak, Malaysia among 11 pig farms, 2 abattoirs, and 3 animal markets in June and July of 2017. Pig feces, pig oral secretions, bioaerosols, and worker nasal wash samples were collected and analyzed via rPCR and rRT-PCR for respiratory and diarrheal viruses.

RESULTS

In all, 55 pig fecal, 49 pig oral or water, 45 bioaerosol, and 78 worker nasal wash samples were collected across 16 sites. PCV2 was detected in 21 pig fecal, 43 pig oral or water, 3 bioaerosol, and 4 worker nasal wash samples. In addition, one or more bioaerosol or pig samples were positive for EV, IAV, and RVC, and one or more worker samples were positive for ADV, CoV, IBV, and IDV.

CONCLUSIONS

This study demonstrates that nucleic acids from a number of targeted viruses were present in pig oral secretions and pig fecal samples, and that several viruses were detected in bioaerosol samples or in the nasal passages of humans with occupational exposure to pigs. These results demonstrate the need for future research in strengthening viral surveillance at the human-animal interface, specifically through expanded bioaerosol sampling efforts and a seroepidemiological study of individuals with exposure to pigs in this region for PCV2 infection.

Phylogenetic analysis of two goat-origin PCV2 isolates in China

Complete genome characterization of non-porcine origin Porcine circovirus type 2 (PCV2) was first described in 2014 in China. In the present study, we first identified PCV2 nucleotides in goat samples and the prevalence of PCV2 in goat was 6.15%. However, only two new strains, Goat2014-4 and Goat2014-5, could be completely sequenced. The genome of the strain Goat2014-4, which collected from the goat infected with PPRV, contains 1766 nt; strain Goat2014-5, which originated from a healthy goat, is comprised of 1767 nt. The results showed that they shared the highest nucleotide identity with BDH and the lowest similarity with DK1980PMWSfree strain and they belonged only to genotype PCV2d. Meanwhile, they shared higher homology with porcine-origin PCV2 strains than others. Moreover, a detailed analysis of the capsid amino acid sequences revealed that there were distinct differences for goat2014-4 (708 bp) and goat2014-5 (705 bp); strain Goat2014-4 showed an elongation of two amino acids, and strains Goat2014-5 showed an elongation of one amino acid compared with other reference strains. This is the first report of the genetic analysis of goat-origin PCV2 isolates. It also provides an additional supported evidence for cross-species transmission of PCV2.

Porcine Circoviruses and Xenotransplantation

Allotransplantation and xenotransplantation may be associated with the transmission of pathogens from the donor to the recipient. Whereas in the case of allotransplantation the transmitted microorganisms and their pathogenic effect are well characterized, the possible influence of porcine microorganisms on humans is mostly unknown. Porcine circoviruses (PCVs) are common in pig breeds and they belong to porcine microorganisms that still have not been fully addressed in terms of evaluating the potential risk of xenotransplantation using pig cells, tissues, and organs. Two types of PCVs are known: porcine circovirus (PCV) 1 and PCV2. Whereas PCV1 is apathogenic in pigs, PCV2 may induce severe pig diseases. Although most pigs are subclinically infected, we do not know whether this infection impairs pig transplant functionality, particularly because PCV2 is immunosuppressive. In addition, vaccination against PCV2 is able to prevent diseases, but in most cases not transmission of the virus. Therefore, PCV2 has to be eliminated to obtain xenotransplants from uninfected healthy animals. Although there is evidence that PCV2 does not infect—at least immunocompetent—humans, animals should be screened using sensitive methods to ensure virus elimination by selection, Cesarean delivery, vaccination, or embryo transfer.

Porcine circovirus type 2 activates PI3K/Akt and p38 MAPK pathways to promote interleukin-10 production in macrophages via Cap interaction of gC1qR

Porcine circovirus type 2 (PCV2) infection caused PCV2-associated diseases (PCVAD) is one of the major emerging immunosuppression diseases in pig industry. In this study, we investigated how PCV2 inoculation increases interleukin (IL)-10 expression in porcine alveolar macrophages (PAMs). PCV2 inoculation significantly upregulated IL-10 expression compared with PCV1. Upon initial PCV2 inoculation, PI3K/Akt cooperated with NF-κB pathways to promote IL-10 transcription via p50, CREB and Ap1 transcription factors, whereas inhibition of PI3K/Akt activation blocked Ap1 and CREB binding to the il10 promoter, and decreased the binding level of NF-κB1 p50 with il10 promoter, leading to great reduction in early IL-10 transcription. In the later phase of inoculation, PCV2 further activated p38 MAPK and ERK pathways to enhance IL-10 production by promoting Sp1 binding to the il10 promoter. For PCV2-induced IL-10 production in macrophages, PCV2 capsid protein Cap, but not the replicase Rep or ORF3, was the critical component. Cap activated PI3K/Akt, p38 MAPK, and ERK signaling pathways to enhance IL-10 expression. In the whole process, gC1qR mediated PCV2-induced PI3K/Akt and p38 MAPK activation to enhance IL-10 induction by interaction with Cap. Depletion of gC1qR blocked PI3K/Akt and p38 MAPK activation, resulting in significant decrease in IL-10 production in PCV2-inoculated cells. Thus, gC1qR might be a critical functional receptor for PCV2-induced IL-10 production. Taken together, these data demonstrated that Cap protein binding with host gC1qR induction of PI3K/Akt and p38 MAPK signalings activation is a critical process in enhancing PCV2-induced IL-10 production in porcine alveolar macrophages.

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

During routine electron microscopy of fecal samples from diarrheic dogs dated from 2000 virus particles resembling circovirus in shape and size were detected in two samples (V2177/00; V3374/00). Polymerase chain reaction (PCR) using primers specific for porcine circovirus type 2 (PCV2) amplified DNA recovered from both samples. Sequencing of PCR amplificates (V2177/00) obtained with PCV2-specific primer pairs revealed a genome size of 1768 bp. The nucleotide sequence was highly similar (98% nucleotide identity) to the PCV2a reference sequence.

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Electron microscopy has revealed circoviruses in two fecal samples of diarrheic dogs.

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PCV2-specific PCR amplified DNA extracted from the samples.

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By sequencing one sample a genome size of 1768 bp and a nucleotide sequence identity of 98% to PCV2a were achieved.

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This is the first time that PCV2 has been reported in dogs.

Circovirus transport proceeds via direct interaction of the cytoplasmic dynein IC1 subunit with the viral capsid protein

Microtubule transport of circovirus from the periphery of the cell to the nucleus is essential for viral replication in early infection. How the microtubule is recruited to the viral cargo remains unclear. In this study, we observed that circovirus trafficking is dependent on microtubule polymerization and that incoming circovirus particles colocalize with cytoplasmic dynein and endosomes. However, circovirus binding to dynein was independent of the presence of microtubular α-tubulin and translocation of cytoplasmic dynein into the nucleus. The circovirus capsid (Cap) subunit enhanced microtubular acetylation and directly interacted with intermediate chain 1 (IC1) of dynein. N-terminal residues 42 to 100 of the Cap viral protein were required for efficient binding to the dynein IC1 subunit and for retrograde transport. Knockdown of IC1 decreased virus transport and replication. These results demonstrate that Cap is a direct ligand of the cytoplasmic dynein IC1 subunit and an inducer of microtubule α-tubulin acetylation. Furthermore, Cap recruits the host dynein/microtubule machinery to facilitate transport toward the nucleus by an endosomal mechanism distinct from that used for physiological dynein cargo.

IMPORTANCE

Incoming viral particles hijack the intracellular trafficking machinery of the host in order to migrate from the cell surface to the replication sites. Better knowledge of the interaction between viruses and virus proteins and the intracellular trafficking machinery may provide new targets for antiviral therapies. Currently, little is known about the molecular mechanisms of circovirus transport. Here, we report that circovirus particles enter early endosomes and utilize the microtubule-associated molecular motor dynein to travel along microtubules. The circovirus capsid subunit enhances microtubular acetylation, and N-terminal residues 42 to 100 directly interact with the dynein IC1 subunit during retrograde transport. These findings highlight a mechanism whereby circoviruses recruit dynein for transport to the nucleus via the dynein/microtubule machinery.

First molecular detection of porcine circovirus type 2 in bovids in China

For the worldwide pig industries, porcine circovirus type 2 (PCV2) is an economically important pathogen. At present, the prevalence of PCV2 is common in Chinese swine herds. However, there is little information on PCV2 prevalence in non-porcine animals in China, such as bovids. Therefore, the goal of this study is to obtain the firsthand prevalence data of PCV2 in bovids in China. Two hundred and eighty serum and muscle samples from dairy cows (n = 180), buffalo (n = 50), and yellow cattle (n = 50) were analyzed by PCR. The detection results show that PCV2 infections (16 %, 8/50) only exist in buffaloes. In addition, there are different PCV2 viral DNAs identified by differential PCR in the same buffalo sample. Nucleotide sequencing and phylogenetic analysis results based on partial ORF1 and ORF2 sequences suggest that PCV2 strains have genetic diversity in buffaloes and they are divided into three different genotypes (PCV2b, PCV2d, and PCV2e, respectively). Moreover, to our knowledge, the PCV2d and PCV2e genotypes have not been previously reported in bovids. Through this study, the firsthand data of PCV2 prevalence in bovids in China was documented.

Susceptibility of calves to porcine circovirus-2 (PCV2)

Circoviruses are known to infect pigs and birds and cause severe diseases with various clinical signs. Porcine circovirus-2 (PCV2), associated with severe economic losses, was detected in rodents, mosquitoes, cattle, and in calves affected with bovine neonatal pancytopenia (BNP). However, molecular and serological investigations on circovirus infections in cattle revealed inconsistent results. The aim of the study was to investigate the susceptibility and immune response of calves to experimental PCV2 inoculation. Animals were either intravenously inoculated with tissue-culture grown PCV2, with bone marrow from PCV2 positive and negative calves or immunized with a commercial inactivated PCV2 vaccine. The results showed that the animals inoculated with tissue-culture grown PCV2 and with PCV2 positive bone marrow displayed clinical signs including lymph node swelling, reddening of oral and ocular mucosa, and diarrhoea 7-18 days post inoculation (p.i.). PCV2-specific antibodies were detected in the tissue-culture grown PCV2-infected animals and in the PCV2-immunized animals from day 11 and 7 p.i. onwards, respectively, but were absent in both bone marrow inoculated groups. PCV2 was detected by real-time quantitative PCR only in blood samples of the tissue-culture grown PCV2-infected animals and in various tissues (e.g. spleen, lymph nodes, thymus), with high copy numbers in blood between day 4 (5.16log10 genomic copy number/ml) and 46 (5.33log10 genomic copy number/ml) p.i. In conclusion, the seroconversion and the detection of PCV2 in lymphoid tissues for more than five weeks p.i. revealed that host susceptibility of PCV2 is not solely restricted to pigs.

The serological evidence in humans supports a negligible risk of zoonotic infection from porcine circovirus type 2

There are two porcine circovirus (PCV) genotypes, PCV-1 and PCV-2. In pigs, PCV-1 infection is asymptomatic but PCV-2 infection can cause severe respiratory disease and other pathology. Although humans ingest PCV-contaminated foods and are exposed to PCV through other sources, the potential of PCV-2 as a zoonotic agent in humans and other species has not been fully explored. Here, four recombinant proteins derived from the PCV-2 capsid gene were examined as antigens using the Luciferase Immunoprecipitation System (LIPS) assay for serological analysis of PCV-2 infection. PCV-2-CAP-Δ1 was the optimum recombinant protein in the LIPS assay with a sensitivity of 93% and specificity of 100% using porcine samples. Testing of healthy human blood donors, equine and bovine serum samples failed to demonstrate the presence of anti-PCV-2 antibodies. Additionally, analysis of two high-risk human groups, cystic fibrosis patients taking porcine derived oral supplements and type I diabetes patients who had undergone porcine islet cell transplantation, showed no evidence of anti-PCV-2 antibodies. These results extend the extensively demonstrated use of LIPS as a robust approach for identifying humoral responses and provide evidence that PCV-2 is likely not infectious in humans.

Isolation and genetic characterization of human coronavirus NL63 in primary human renal proximal tubular epithelial cells obtained from a commercial supplier, and confirmation of its replication in two different types of human primary kidney cells

Background

Cryopreserved primary human renal proximal tubule epithelial cells (RPTEC) were obtained from a commercial supplier for studies of Simian virus 40 (SV40). Within twelve hrs after cell cultures were initiated, cytoplasmic vacuoles appeared in many of the RPTEC. The RPTEC henceforth deteriorated rapidly. Since SV40 induces the formation of cytoplasmic vacuoles, this batch of RPTEC was rejected for the SV40 study. Nevertheless, we sought the likely cause(s) of the deterioration of the RPTEC as part of our technology development efforts.

Methods

Adventitious viruses in the RPTEC were isolated and/or detected and identified by isolation in various indicator cell lines, observation of cytopathology, an immunoflurorescence assay, electron microscopy, PCR, and sequencing.

Results

Cytomegalovirus (CMV) was detected in some RPTEC by cytology, an immunofluorescence assay, and PCR. Human Herpesvirus 6B was detected by PCR of DNA extracted from the RPTEC, but was not isolated. Human coronavirus NL63 was isolated and identified by RT-PCR and sequencing, and its replication in a fresh batch of RPTEC and another type of primary human kidney cells was confirmed.

Conclusions

At least 3 different adventitious viruses were present in the batch of contaminated RPTEC. Whereas we are unable to determine whether the original RPTEC were pre-infected prior to their separation from other kidney cells, or had gotten contaminated with HCoV-NL63 from an ill laboratory worker during their preparation for commercial sale, our findings are a reminder that human-derived biologicals should always be considered as potential sources of infectious agents. Importantly, HCoV-NL63 replicates to high titers in some primary human kidney cells.

In vivo characterization of chimeric PCV DNA clones containing heterogeneous capsid protein nuclear localization signals (NLS)

Background

PCV ORF2 capsid protein was predicted to contribute to the control of replication via an interaction between the Cap and Rep proteins in the nucleoplasm. We previously showed that the nuclear localization signal (NLS) on the capsid protein plays an accessory role in the replication of PCV in vitro. To further evaluate the in vivo characteristics of NLS-chimeric PCV DNA clones, BALB/C mice were inoculated intranasally and intraperitoneally with the DNA clones.

Results

As expected, no gross lesions were detected during the study of the inoculated animals. The chimeric PCV12-, PCV1-NLS2- and PCV2-NLS1-inoculated animals had significantly fewer and less severe histopathological lesions in lymphoid tissues than the PCV2-inoculated animals (P < 0.05). PCV12 induced a specific antibody response against PCV2 ORF2 comparable to that induced by wild-type PCV2 but demonstrated a shorter period of viremia and much lower level of virus loads in sera than those in PCV2-inoculated mice. Remarkably, the PCV2-NLS1 and PCV1-NLS2 chimeras replicated in inoculated mice and induced specific antibody responses but failed to produce viral antigens in the lymph nodes or a detectable viremia.

Conclusions

The chimeric PCV2-NLS1 and PCV1-NLS2 demonstrated a lower replication level as compared with wild type of PCV2 or PCV1 in vivo, suggesting that ORF2 NLSs played an accessory role in PCV replication. The chimeric PCV12 is a good candidate for vaccination against PCV2 infection.

Development of an immunochromatographic strip for the detection of antibodies against Porcine circovirus-2

A rapid (<5 min) immunochromatographic strip using a colloidal gold–labeled antigen probe was successfully developed and applied for the detection of Porcine circovirus-2 (PCV-2) antibodies in swine. Recombinant Cap protein truncated nuclear localization signal of PCV-2, was expressed and labeled with colloidal gold. This conjugate was dispensed on a conjugate pad as the detector. Staphylococcal protein A and purified porcine anti–PCV-2 antibodies were blotted on a nitrocellulose membrane for the test and control lines, respectively. Sensitivity and specificity of this strip test was evaluated using PCV-2 antisera as well as other sera from pigs infected with a variety of swine viruses. For the validation of this strip test, 500 clinical swine serum samples were assessed both by the strip and a commercial enzyme-linked immunosorbent assay (ELISA) kit. The agreement between the immunochromatographic strip and ELISA kit was 94.00%. This strip possesses high sensitivity and specificity and may be useful as a candidate for rapid diagnosis of PCV-2 antibodies in the field.

Circoviruses: immunosuppressive threats to avian species: a review

Circoviruses are small, non-enveloped, icosahedral viruses that are unique among animal viruses in having circular, single-stranded DNA genomes. Their genomes are also the smallest possessed by animal viruses. The circovirus family currently comprises three members, chicken anaemia virus, porcine circovirus, and psittacine beak and feather disease virus, with pigeon circovirus being classified as a tentative member. Infections with each of the four circoviruses are associated with potentially fatal diseases in which virus-induced damage to lymphoid tissue and immunosuppression are common features. Experience with other animal virus families suggests that additional animal species will be infected by, as yet undiscovered, circoviruses and that these may display similar tissue tropism and disease-causing potential. Recent reports describing the association of circovirus-like viruses with immunodeficiency-related diseases of geese and southern black-backed gulls suggest that circovirus infections of avian species may be more common than previously recognized, and prompt the question of whether novel circoviruses infect poultry to cause clinical and/or subclinical diseases that may be economically important. This review has three purposes. First, it is designed to summarize the currently available information about the classified circoviruses and viruses that are regarded as circovirus-like. Second, it aims to alert the readership to the possibility that other avian species, including commercial poultry, may be infected with novel circoviruses. Finally, possible methods for discovering novel circoviruses and for controlling infections by such viruses are suggested.

A novel porcine circovirus-like agent P1 is associated with wasting syndromes in pigs

A novel porcine pathogen tentatively named P1, which was obtained from the sera of the pigs exhibiting clinical signs of postweaning multisystemic wasting syndrome (PMWS) experimentally caused the classical clinic signs and pathologic lesions of the disease in pigs by direct in vivo injection with P1 DNA plasmids. Twenty colostrum-fed (CF) pigs that were free of PCV2 and P1 at 1 month of age were randomly designated equally to two groups. Group 1 pigs were each injected with 400 µg of the cloned P1 plasmid DNA into the superficial inguinal lymph nodes and Group 2 were injected with same amount of the empty pSK vector DNA and served as controls. Viremias were positively detected in 8 of 10 P1 infected pigs from 14–21 days post-inoculation (dpi). The 8 infected animals showed pallor of skin and diarrhea. Gross lesions in the pigs euthanized on 35 dpi were similarly characterized by encephalemia, haemorrhage of the bladder mucosa, haemorrhage of the superficial inguinal lymph nodes, lung atrophy and haemorrhage. Histopathological lesions were arteriectasis and telangiectasia of the cavitas subarachnoidealis, interstitial pneumonia, mild atrophy of the cardiac muscle cells, histiocytic hyperplasia of the follicles in the tonsils, and haemorrhage of the inguinal lymph nodes. P1 DNA and antigens were confirmed by PCR and immunohistochemistry in the tissues and organs of the infected pigs, including the pancreas, bladders, testicles/ovaries, brains, lungs and liver. There were no obvious clinical signs and pathological lesions in the control pigs. This study demonstrated that P1 infection is one of the important pathologic agents on pig farms.

Rapidly expanding genetic diversity and host range of the Circoviridae viral family and other Rep encoding small circular ssDNA genomes

The genomes of numerous circoviruses and distantly related circular ssDNA viruses encoding a rolling circle replication initiator protein (Rep) have been characterized from the tissues of mammals, fish, insects, plants (geminivirus and nanovirus), in human and animal feces, in an algae cell, and in diverse environmental samples. We review the genome organization, phylogenetic relationships and initial prevalence studies of cycloviruses, a proposed new genus in the Circoviridae family. Viral fossil rep sequences were also recently identified integrated on the chromosomes of mammals, frogs, lancelets, crustaceans, mites, gastropods, roundworms, placozoans, hydrozoans, protozoans, land plants, fungi, algae, and phytoplasma bacterias and their plasmids, reflecting the very wide past host range of rep bearing viruses. An ancient origin for viruses with Rep-encoding small circular ssDNA genomes, predating the diversification of eukaryotes, is discussed. The cellular hosts and pathogenicity of many recently described rep-containing circular ssDNA genomes remain to be determined. Future studies of the virome of single cell and multi-cellular eukaryotes are likely to further extend the known diversity and host-range of small rep-containing circular ssDNA viral genomes.

Emerging and re-emerging swine viruses

In the past two decades or so, a number of viruses have emerged in the global swine population. Some, such as porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2), cause economically important diseases in pigs, whereas others such as porcine torque teno virus (TTV), now known as Torque teno sus virus (TTSuV), porcine bocavirus (PBoV) and related novel parvoviruses, porcine kobuvirus, porcine toroviruses (PToV) and porcine lymphotropic herpesviruses (PLHV), are mostly subclinical in swine herds. Although some emerging swine viruses such as swine hepatitis E virus (swine HEV), porcine endogenous retrovirus (PERV) and porcine sapovirus (porcine SaV) may have a limited clinical implication in swine health, they do pose a potential public health concern in humans due to zoonotic (swine HEV) or potential zoonotic (porcine SaV) and xenozoonotic (PERV, PLHV) risks. Other emerging viruses such as Nipah virus, Bungowannah virus and Menangle virus not only cause diseases in pigs but some also pose important zoonotic threat to humans. This article focuses on emerging and re-emerging swine viruses that have a limited or uncertain clinical and economic impact on pig health. The transmission, epidemiology and pathogenic potential of these viruses are discussed. In addition, the two economically important emerging viruses, PRRSV and PCV2, are also briefly discussed to identify important knowledge gaps.

Evaluation of the human host range of bovine and porcine viruses that may contaminate bovine serum and porcine trypsin used in the manufacture of biological products

Current U.S. requirements for testing cell substrates used in production of human biological products for contamination with bovine and porcine viruses are U.S. Department of Agriculture (USDA) 9CFR tests for bovine serum or porcine trypsin. 9CFR requires testing of bovine serum for seven specific viruses in six families (immunofluorescence) and at least 2 additional families non-specifically (cytopathicity and hemadsorption). 9CFR testing of porcine trypsin is for porcine parvovirus. Recent contaminations suggest these tests may not be sufficient. Assay sensitivity was not the issue for these contaminations that were caused by viruses/virus families not represented in the 9CFR screen. A detailed literature search was undertaken to determine which viruses that infect cattle or swine or bovine or porcine cells in culture also have human host range [ability to infect humans or human cells in culture] and to predict their detection by the currently used 9CFR procedures. There are more viruses of potential risk to biological products manufactured using bovine or porcine raw materials than are likely to be detected by 9CFR testing procedures; even within families, not all members would necessarily be detected. Testing gaps and alternative methodologies should be evaluated to continue to ensure safe, high quality human biologicals.

Coreplication of the major genotype group members of porcine circovirus type 2 as a prerequisite to coevolution may explain the variable disease manifestations

A member of the family Circoviridae, porcine circovirus type 2 (PCV2), is associated with postweaning multisystemic wasting syndrome (PMWS), a recent emerging disease worldwide. PCV2 is also found in clinically asymptomatic animals. This paradoxical finding makes the syndrome etiology challenging. We developed new assays to study PCV2 with links to syndrome etiology. For analysis, we used PCV2-infected tissues from subclinically infected and diseased piglets. We compared antigen- and PCV2 DNA-derived signals for tissue localization and intensity. Oligonucleotides were designed to the signature motif of the PCV2 capsid open reading frame to discriminate experimentally between PCV2 genotype groups by PCR, in situ hybridization (ISH), and fluorescence in situ hybridization (FISH). Unexpectedly, all PCV2-infected animals carried both PCV2a and PCV2b genotype group members. Using confocal microscopy, genotype single-cell infections and cell superinfections were visible. Additionally, we discriminated replicative DNA from total PCV2 DNA isoforms with FISH. This aided in our inquiry into cellular genotype-specific replication. Importantly, single-genotype-group replication was not observed. In infected cells with replicating virus, both genotype groups were equally present. These findings suggest PCV2 genotype group members relaxed replication regulation requirements and may even point to PCV2 replication cooperativity in vivo. These observations explain the readily seen PCV2 DNA recombinations and the high overall PCV2 genome plasticity. Hence, we suggest a novel mechanism of syndrome etiology that consists of a continuously changing PCV2 genome pool in hosts and pig herds, posing a constant challenge to the individual maturing immune system.

Epidemiology and horizontal transmission of porcine circovirus type 2 (PCV2)

Porcine circovirus type 2 (PCV2) is a small, non-enveloped, circular, single-stranded DNA virus of economic importance in the swine industry worldwide. Based on the sequence analyses of PCV2 strains, isolates can be divided into five subtypes (PCV2a–e). PCV2 is an ubiquitous virus based on serological and viremia data from countries worldwide. In addition, PCV2 DNA was discovered in archived samples prior to the first recognition of clinical disease. Recently, a worldwide shift in PCV2 subtype from PCV2a to PCV2b occurred. PCV2 DNA can be detected in fecal, nasal, oral and tonsillar swabs as well as in urine and feces from both naturally and experimentally infected pigs. PCV2 DNA can be detected early in the infectious process and persists for extended periods of time. The effectiveness of disinfectants for reducing PCV2in vitrois variable and PCV2 is very stable in the pig environment. Limited data exist on the horizontal transmission of PCV2. Direct transmission of PCV2 between experimentally or naturally infected animals and naïve animals has been documented and the incorporation of clinical or subclinically infected animals into a population represents a risk to the herd. Indirect transmission through the oral, aerosol or vaccine routes is likely a lesser risk for the transmission of PCV2 in most swine populations but may be worth evaluating in high heath herds. The objective of this review was to discuss data on the epidemiology and horizontal transmission of PCV2.

Analysis of porcine circovirus type 1 detected in Rotarix vaccine

A metagenomic analysis of live human vaccines has recently demonstrated the presence of porcine circovirus type 1 (PCV1) DNA in the paediatric vaccine Rotarix used in the prevention of acute gastroenteritis. Using real-time PCR for PCV1, titres of PCV1 DNA in several batches of Rotarix were found to be in the order of 6-7 log(10) copies per dose. Pre-treatment of the reconstituted vaccine with the nuclease Benzonase, followed by extraction of nucleic acid and quantification of PCV1 DNA by real-time PCR, revealed that there was no loss of PCV1 DNA titre compared to untreated controls, suggesting that the porcine viral DNA was present in the vaccine in an encapsidated form. PCV1 permissive PS cells, human HEK293 and Vero cells, used for vaccine production, were infected with Rotarix or PCV1, respectively, and subjected to immune fluorescence and RT-PCR. Viral genomes were present in Rotarix-incubated as well as PCV1-infected cells, while viral transcription was seen only in PCV1-infected cells. Similarly, PCV1-specific protein expression was observed in PCV1-infected cells, but not in cells treated with Rotarix. Passaging of the supernatant indicated productive infection in PCV1-infected PS cells, but not in HEK293 and Vero cells or in any cell line incubated with Rotarix. PCV1 DNA present in Rotarix was protected from Benzonase digestion; however, PCV1 was not recognized in immune electron microscopy and unable to infect PS, HEK293 or Vero cells, suggesting that the high amount of PCV1 DNA present in Rotarix does not reflect a corresponding proportion of biologically active virus particles.

Viral nucleic acids in live-attenuated vaccines: detection of minority variants and an adventitious virus

Metagenomics and a panmicrobial microarray were used to examine eight live-attenuated viral vaccines. Viral nucleic acids in trivalent oral poliovirus (OPV), rubella, measles, yellow fever, varicella-zoster, multivalent measles/mumps/rubella, and two rotavirus live vaccines were partially purified, randomly amplified, and pyrosequenced. Over half a million sequence reads were generated covering from 20 to 99% of the attenuated viral genomes at depths reaching up to 8,000 reads per nucleotides. Mutations and minority variants, relative to vaccine strains, not known to affect attenuation were detected in OPV, mumps virus, and varicella-zoster virus. The anticipated detection of endogenous retroviral sequences from the producer avian and primate cells was confirmed. Avian leukosis virus (ALV), previously shown to be noninfectious for humans, was present as RNA in viral particles, while simian retrovirus (SRV) was present as genetically defective DNA. Rotarix, an orally administered rotavirus vaccine, contained porcine circovirus-1 (PCV1), a highly prevalent nonpathogenic pig virus, which has not been shown to be infectious in humans. Hybridization of vaccine nucleic acids to a panmicrobial microarray confirmed the presence of endogenous retroviral and PCV1 nucleic acids. Deep sequencing and microarrays can therefore detect attenuated virus sequence changes, minority variants, and adventitious viruses and help maintain the current safety record of live-attenuated viral vaccines.

Multiple diverse circoviruses infect farm animals and are commonly found in human and chimpanzee feces

Circoviruses are known to infect birds and pigs and can cause a wide range of severe symptoms with significant economic impact. Using viral metagenomics, we identified circovirus-like DNA sequences and characterized 15 circular viral DNA genomes in stool samples from humans in Pakistan, Nigeria, Tunisia, and the United States and from wild chimpanzees. Distinct genomic features and phylogenetic analysis indicate that some viral genomes were part of a previously unrecognized genus in the Circoviridae family we tentatively named "Cyclovirus" whose genetic diversity is comparable to that of all the known species in the Circovirus genus. Circoviridae detection in the stools of U.S. adults was limited to porcine circoviruses which were also found in most U.S. pork products. To determine whether the divergent cycloviruses found in non-U.S. human stools were of dietary origin, we genetically compared them to the cycloviruses in muscle tissue samples of commonly eaten farm animals in Pakistan and Nigeria. Limited genetic overlap between cycloviruses in human stool samples and local cow, goat, sheep, camel, and chicken meat samples indicated that the majority of the 25 Cyclovirus species identified might be human viruses. We show that the genetic diversity of small circular DNA viral genomes in various mammals, including humans, is significantly larger than previously recognized, and frequent exposure through meat consumption and contact with animal or human feces provides ample opportunities for cyclovirus transmission. Determining the role of cycloviruses, found in 7 to 17% of non-U.S. human stools and 3 to 55% of non-U.S. meat samples tested, in both human and animal diseases is now facilitated by knowledge of their genomes.

Porcine circovirus type 2 and porcine circovirus-associated disease

Porcine circovirus type 2 (PCV2) belongs to the viral family Circoviridae and to the genus Circovirus. Circoviruses are small, single-stranded nonenveloped DNA viruses that have an unsegmented circular genome. PCV2 is the primary causative agent of several syndromes collectively known as porcine circovirus-associated disease (PCVAD). Many of the syndromes associated with PCVAD are a result of coinfection with PCV2 virus and other agents such as Mycoplasma and porcine reproductive and respiratory syndrome virus. PCV2 infection is present in every major swine-producing country in the world, and the number of identified cases of PCVAD is rapidly increasing. In the United States, the disease has cost producers an average of 3-4 dollars per pig with peak losses ranging up to 20 dollars per pig. The importance of this disease has stimulated investigations aimed at identifying risk factors associated with infection and minimizing these risks through modified management practices and development of vaccination strategies. This paper provides an overview of current knowledge relating to PCV2 and PCVAD with an emphasis on information relevant to the swine veterinarian.

Protective immunity against porcine circovirus 2 in mice induced by a gene-based combination vaccination

BACKGROUND

Porcine circovirus type 2 (PCV2) is the primary cause of an emerging swine disease, postweaning multisystemic wasting syndrome, that is responsible for economic losses. To develop an effective vaccine for PCV2, we evaluated a heterologous prime-boost vaccine approach, using a gene gun-mediated naked DNA vector as a priming and modified vaccinia virus ankara (MVA) as a booster, in Balb/c mice.

METHODS

Three open reading frames (ORF) of PCV2 viral samples from infected pigs were amplified, and gene gun-mediated DNA priming vaccination was performed followed by boosts with MVA vectors expressing the same ORFs of PCV2. After vaccination, mice were challenged with PCV2 virus, and virus titers in the lungs and lymph nodes were measured.

RESULTS

The combination of ORF-2 and -3 in this gene-based vaccine strategy resulted in high antibody titers and virus neutralization activity in serum, reduced PCV2 virus load, and reduced levels of apoptosis in the lungs. No cross-reaction was observed between ORF-1 and -2, but weak cross-reaction was observed between ORF-1 and -3, and between ORF-2 and -3. Following vaccination, expression of chemokines, macrophage inflammatory protein-1beta and regulated upon activation, normal T cell expressed and secreted, increased significantly. The expression of T helper 1-type cytokine (interferon-gamma) and specific lysis of PCV2-infected cells increased; concomitantly, the level of T helper 2-type cytokine (interleukin-10) decreased in test mice. The expression of tumor necrosis factor-alpha and granulocyte-macrophage colony-stimulating factor increased significantly in mice vaccinated with ORF-2/-3, and with ORF-1/-2/-3.

CONCLUSIONS

This prime-boost vaccination strategy, using a gene gun for DNA priming and recombinant MVA for boosts, may be an attractive vaccine strategy against PCV2 infection in swine.

Porcine circovirus type 2 associated disease: update on current terminology, clinical manifestations, pathogenesis, diagnosis, and intervention strategies

Porcine circovirus type 2 (PCV2)-associated disease (PCVAD) continues to be an important differential diagnosis on pig farms in the United States and worldwide. Case trend analyses indicate that the incidence of PCVAD is on the rise in the United States. Accurate diagnosis is important in order to implement appropriate intervention strategies. PCVAD can manifest as a systemic disease, as part of the respiratory disease complex, as an enteric disease, as porcine dermatitis and nephropathy syndrome, or as reproductive problems. PCVAD may be only a sporadic individual animal diagnosis; however, PCVAD may also manifest as a severe herd problem accelerated and enhanced by concurrent virus or bacterial infections. This article is intended to discuss the most common disease manifestations, pathogenesis, diagnostic approaches, and intervention strategies associated with PCVAD in North America.

Porcine circovirus diseases

Porcine circovirus type 2 (PCV2) is a member of the familyCircoviridae, a recently established virus family composed of small, non-enveloped viruses, with a circular, single-stranded DNA genome. PCV2, which is found all over the world in the domestic pig and probably the wild boar, has been recently associated with a number of disease syndromes, which have been collectively named porcine circovirus diseases (PCVD). Postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS) and reproductive disorders are the most relevant ones. Among them, only PMWS is considered to have a severe impact on domestic swine production. PMWS mainly affects nursery and/or fattening pigs; wasting is considered the most representative clinical sign in this disease. Diagnosis of this disease is confirmed by histopathological examination of lymphoid tissues and detection of a moderate to high amount of PCV2 in damaged tissues. Since PMWS is considered a multifactorial disease in which other factors in addition to PCV2 are needed in most cases to trigger the clinical disease, effective control measures have focused on the understanding of the co-factors involved in individual farms and the control or elimination of these triggers. PDNS, an immuno-complex disease characterized by fibrino-necrotizing glomerulonephritis and systemic necrotizing vasculitis, has been linked to PCV2, but a definitive proof of this association is still lacking. PCV2-associated reproductive disease seems to occur very sporadically under field conditions, but it has been characterized by late-term abortions and stillbirths, extensive fibrosing and/or necrotizing myocarditis in fetuses and the presence of moderate to high amounts of PCV2 in these lesions. Taking into account that scientific information on PCV2 and its associated diseases has been markedly expanded in the last 8 years, the objective of this review is to summarize the current state of knowledge of the most relevant aspects of PCV2 biology and PCVD.

The ORF3 protein of porcine circovirus type 2 is involved in viral pathogenesis in vivo

Porcine circovirus type 2 (PCV2) is the primary causative agent of an emerging swine disease, postweaning multisystemic wasting syndrome. We previously showed that a novel identified protein, ORF3, was not essential for PCV2 replication in cultured PK15 cells and played a major role in virus-induced apoptosis. To evaluate the role of the ORF3 protein in viral pathogenesis in vivo, we inoculated 8-week-old BALB/c mice that have been developed for PCV2 replication with ORF3-deficient mutant PCV2 (mPCV2). By 42 days postinoculation, all of the mice inoculated with the mPCV2, as well as with wild-type PCV2 (wPCV2), had seroconverted to PCV2 capsid antibody, and the mutant induced levels of PCV2 antibodies that were higher than those of the wPCV2. The PCV2 genomic copy numbers in serum were significantly higher (P<0.05) in the wPCV2-inoculated mice than in mice inoculated with the mPCV2. Also, the wPCV2 caused microscopic lesions characterized by lymphocyte depletion with histiocytic infiltration of lymphoid organs, but the mutant virus failed to induce any obvious pathological lesions. In situ hybridization and immunohistochemical analyses also showed that larger amounts of viral DNA and antigens were detected in the lymph nodes of the wPCV2-inoculated than mPCV2-inoculated mice. Furthermore, animals of the wPCV2-inoculated group showed significant downshifts of CD8(+) T-cell subsets of peripheral blood lymphocytes compared to the control mice (P<0.05) at various time points postinoculation. Also, the proportions of the CD4(+) and CD4(+) CD8(+) cells were significantly reduced in wPCV2-inoculated mice at some time points postinoculation. In contrast, there are some reductions in the proportions of these subsets in the mutant virus-inoculated mice, but the proportions do not decrease significantly. Taken together, these results demonstrate that the ORF3 protein is also dispensable for viral replication in vivo and that it plays an important role in viral pathogenesis.

Ultrastructural alterations in human blood leukocytes induced by porcine circovirus type 1 infection

BACKGROUND

Swine infectious pathogens, especially viruses, represent a potential public health risk associated with the use of pig tissues for xenotransplantation in humans. We hypothesized that porcine circovirus type I (PCV-1) may infect human mononuclear cells, resulting in ultrastructural alterations of the target cells.

METHODS

Transmission electron microscopy was used for evaluating ultrastructural alterations of human cells exposed to a PCV-infected PK15 cell line. A polymerase chain reaction (PCR) assay and fluorescence in situ hybridization (FISH) were developed for detecting PCV-1 in human mononuclear cells.

RESULTS

Morphological alterations of the human T cells exposed to PCV PK15 showed ''boomerang-shaped'' intracytoplasmic inclusions. Nucleocapsids appeared free, close to the nucleus, or contained into cytoplasmic vacuoles. Virions were observed near the surface of the human cells. A considerable number of mature virions and immature forms could be observed in the human cells that had a completely intact nuclear membrane with no alteration in the disposition of chromatin. PCV-1 particles were identified budding into typical Golgi saccules and vacuoles. Virions sized up to 23 nm in diameter, and appeared in the nucleus and in the periphery of the cellular core. PCV-1 infection was detected on CD4+, CD8+, CD14+, CD19+, and CD56+ human cells by PCR assay and FISH.

CONCLUSIONS

These results suggest that PCV has the capability of infecting human leukocytes in vitro, and should be considered a potential risk of viral transmission during xenotransplantation.

Assessing the risk potential of porcine circoviruses for xenotransplantation: consensus primer-PCR-based search for a human circovirus

BACKGROUND

An important issue with respect to virus safety in xenotransplantation is the search for human analogues of porcine viruses, because transmission of a porcine virus followed by recombination with a related human virus may lead to a new emerging virus of unknown pathogenicity, host range and virulence. In case of circoviruses, two types of porcine circovirus (PCV1 and PCV2) are described, but the existence of an analogous human circovirus has not yet been investigated.

METHODS

This study describes the analysis of human samples with a consensus primer-PCR approach designed to amplify conserved regions from the rep gene of circoviruses from the genus Circovirus. DNA from human sera, lymph nodes, blood and urine was extracted and investigated with this method that has led previously to the identification of a new avian circovirus.

RESULTS

By screening 1101 samples (there of 168 from immunocompromised patients), no evidence for the existence of a human circovirus related to the genus Circovirus was obtained.

CONCLUSIONS

This result renders the existence of a human circovirus related to the porcine circoviruses more unlikely, nevertheless the presence of such a virus cannot be ruled out.

Monitoring for presence of potentially xenotic viruses in recipients of pig islet xenotransplantation

This study represents a long-term follow-up of human patients receiving pig islet xenotransplantation. Eighteen patients had been monitored for up to 9 years for potentially xenotic pig viruses: pig endogenous retrovirus, pig cytomegalovirus, pig lymphotropic herpesvirus, and pig circovirus type 2. No evidence of viral infection was found.

Identification of pig circovirus type 2 in New Zealand pigs

Interest in porcine circovirus has been stimulated by the recent emergence of postweaning multisystemic wasting syndrome (PMWS) in pigs and the potential use of pig organs for xenotransplantation in humans. Porcine circovirus type 1 (PCV1) is considered to be widespread in pigs but nonpathogenic. Circovirus type 2 (PCV2) is a similar virus but has been differentiated only recently as a separate type. High tissue concentrations of PCV2 are associated with lesions in PMWS cases, but the etiological role of this agent in the disease remains unclear. The presence of PCV1 in New Zealand pigs has been previously reported based on serological data. PMWS has been recently recorded in New Zealand pigs. The epidemiology of PCV2 in New Zealand pigs has not been examined. The purpose of the study was to look for evidence of circoviruses in New Zealand pig herds. Pig circovirus DNA was sought in various tissues using the polymerase chain reaction. Circovirus type 2 was found in New Zealand pig herds, without any evidence that PMWS has ever occurred in these herds. Newborn piglets were shown to have infection, suggesting vertical transmission of the virus.

Infection studies on human cell lines with porcine circovirus type 1 and porcine circovirus type 2

BACKGROUND

The lack of human donor organs in allotransplantation has led to a proposal for the use of porcine tissues and organs as alternative therapeutic material for humans. Besides immunological problems like graft rejection, one of the major concerns is the transmission of porcine microorganisms as viruses, bacteria and fungi to a human recipient.

METHODS

Human cell lines have been infected with porcine circovirus type 1 (PCV1) and porcine circovirus type 2 (PCV2) to investigate whether PCV can infect and replicate in human epithelial cells and lymphocytes. Infection of PCV1 was observed with 293, Hela and Chang liver cells, infection with PCV2 only in Rd cells. In addition, religated viral DNA of PCV1 and PCV2 has been used to transfect adherent human cell lines.

RESULTS

PCV1 persisted in most cell lines without causing any visible changes, while PCV2-transfected cells showed a cytopathogenic effect. Presence of PCV DNA was detected in cells and supernatant by PCR, expression of viral proteins by an indirect immune fluorescence assay. A replication assay showed that the replication of PCV DNA was initiated at the origin of replication. When virus-free cells were inoculated with the supernatant of PCV-infected human cells, the infection was not passed.

CONCLUSION

Although PCV gene expression and replication took place in human cells, the infection is non-productive. Alteration of protein localization suggests that protein targeting may be disturbed in human cells.

Immunogenicity and pathogenicity of chimeric infectious DNA clones of pathogenic porcine circovirus type 2 (PCV2) and nonpathogenic PCV1 in weanling pigs

Porcine circovirus type 2 (PCV2) is the primary causative agent of postweaning multisystemic wasting syndrome (PMWS), whereas the ubiquitous porcine circovirus type 1 (PCV1) is nonpathogenic for pigs. We report here the construction and characterization of two chimeric infectious DNA clones of PCV1 and PCV2. The chimeric PCV1-2 clone contains the PCV2 capsid gene cloned in the backbone of the nonpathogenic PCV1 genome. A reciprocal chimeric PCV2-1 DNA clone was also constructed by replacing the PCV2 capsid gene with that of PCV1 in the backbone of the PCV2 genome. The PCV1, PCV2, and chimeric PCV1-2 and PCV2-1 DNA clones were all shown to be infectious in PK-15 cells, and their growth characteristics in vitro were determined and compared. To evaluate the immunogenicity and pathogenicity of the chimeric infectious DNA clones, 40 specific-pathogen-free (SPF) pigs were randomly assigned into five groups of eight pigs each. Group 1 pigs received phosphate-buffered saline as the negative control. Group 2 pigs were each injected in the superficial inguinal lymph nodes with 200 micro g of the PCV1 infectious DNA clone. Group 3 pigs were each similarly injected with 200 micro g of the PCV2 infectious DNA clone, group 4 pigs were each injected with 200 micro g of the chimeric PCV1-2 infectious DNA clone, and group 5 pigs were each injected with 200 micro g of the reciprocal chimeric PCV2-1 infectious DNA clone. As expected, seroconversion to antibodies to the PCV2 capsid antigen was detected in group 3 and group 4 pigs. Group 2 and 5 pigs all seroconverted to PCV1 antibody. Gross and microscopic lesions in various tissues of animals inoculated with the PCV2 infectious DNA clone were significantly more severe than those found in pigs inoculated with PCV1, chimeric PCV1-2, and reciprocal chimeric PCV2-1 infectious DNA clones. These data indicated that the chimeric PCV1-2 virus with the immunogenic ORF2 capsid gene of pathogenic PCV2 cloned into the nonpathogenic PCV1 genomic backbone induces a specific antibody response to the pathogenic PCV2 capsid antigen but is attenuated in pigs. Future studies are warranted to evaluate the usefulness of the chimeric PCV1-2 infectious DNA clone as a genetically engineered live-attenuated vaccine against PCV2 infection and PMWS.

Exogenous porcine viruses

Porcine organs, cells and tissues provide a viable source of transplants in humans, though there is some concern of public health risk from adaptation of swine infectious agents in humans. Limited information is available on the public health risk of many exogenous swine viruses, and reliable and rapid diagnostic tests are available for only a few of these. The ability of several porcine viruses to cause transplacental fetal infection (parvoviruses, circoviruses, and arteriviruses), emergence or recognition of several new porcine viruses during the last two decades (porcine circovirus, arterivirus, paramyxoviruses, herpesviruses, and porcine respiratory coronavirus) and the immunosuppressed state of the transplant recipients increases the xenozoonoses risk of humans to porcine viruses through transplantation. Much of this risk can be eliminated with vigilance and sustained monitoring along with a better understanding of pathogenesis and development of better diagnostic tests. In this review we present information on selected exogenous viruses, highlighting their characteristics, pathogenesis of viral infections in swine, methods for their detection, and the potential xenozoonoses risk they present. Emphasis has been given in this review to swine influenza virus, paramyxovirus (Nipah virus, Menagle virus, LaPiedad paramyxovirus, porcine paramyxovirus), arterivirus (porcine reproductive and respiratory syndrome virus) and circovirus as either they represent new swine viruses or present the greatest risk. We have also presented information on porcine parvovirus, Japanese encephalitis virus, encephalomyocarditis virus, herpesviruses (pseudorabies virus, porcine lymphotropic herpesvirus, porcine cytomegalovirus), coronaviruses (TGEV, PRCV, HEV, PEDV) and adenovirus. The potential of swine viruses to infect humans needs to be assessed in vitro and in vivo and rapid and more reliable diagnostic methods need to be developed to assure safe supply of porcine tissues and cells for xenotransplantation.

Monitoring for potentially xenozoonotic viruses in New Zealand pigs

Shortage of human donor organs for transplantation has prompted evaluation of animals as an alternative donor source. Pigs are the most acceptable candidate animals but issues of xenozoonozes remain. Despite careful monitoring of high-health-status (HHS) pigs, there is still a risk that their tissues may carry infectious agents. Furthermore, pathogens which are significant in xenotransplantation are not necessarily those of veterinary importance. The detection of these potentially transmissible infectious agents may require the development and application of new surveillance technologies. We present data on monitoring for five potentially xenotic viruses in New Zealand pig herds, namely pig cytomegalovirus (PCMV), pig lymphotropic herpesvirus (PLHV), encephalomyocarditis virus (EMCV), pigcircovirus (PCV), and hepatitis E virus (HEV). These five viruses are either potentially oncogenic, establish persistent infection, or are known to be zoonotic. This study has expanded significantly the information on porcine viruses in New Zealand. Using this information, it is now possible to complete protocols for monitoring pig herds and tissues prior to their use in xenotransplantation. The study resulted in selection of a possible source herd for swine-to-human islet transplantation.