Reproduction of lesions of postweaning multisystemic wasting syndrome in gnotobiotic piglets

Molecular Survey on Porcine Parvoviruses (PPV1-7) and Their Association with Major Pathogens in Reproductive Failure Outbreaks in Northern Italy

Successful reproductive performance is key to farm competitiveness in the global marketplace. Porcine parvovirus 1 (PPV1) has been identified as a major cause of reproductive failure, and since 2001 new species of porcine parvoviruses, namely PPV2-7, have been identified, although their role is not yet fully understood yet. The present study aimed to investigate PPVs' presence in reproductive failure outbreaks occurring in 124 farms of northern Italy. Fetuses were collected from 338 sows between 2019 and 2021 and tested for PPVs by real-time PCR-based assays and for other viruses responsible for reproductive disease. At least one PPV species was detected in 59.7% (74/124) of the tested farms. In order, PPV1, PPV5, PPV6, PPV7 and PPV4 were the most frequently detected species, whereas fewer detections were registered for PPV2 and PPV3. Overall, the new PPV2-7 species were detected in 26.6% (90/338) of the cases, both alone or in co-infections: PCV-2 (7.1%, 24/338), PCV-3 (8.2%, 28/338), and PRRSV-1 (6.2%, 21/338) were frequently identified in association with PPVs. Single PPVs detections or co-infections with other agents commonly responsible for reproductive failure should encourage future studies investigating their biological, clinical, and epidemiological role, for a better preparedness for potential emerging challenges in intensive pig production.

Porcine IGFBP3 promotes porcine circovirus type 2 replication via PERK/eIF2α mediated DNA damage

The infection of porcine circovirus type 2 (PCV2) triggers activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathway and leads to DNA damage. Insulin-like growth factor-binding protein 3 (IGFBP3) may interact with the endoplasmic reticulum (ER). It remains unclear whether IGFBP3 regulates DNA damage via ER stress to mediate PCV2 replication. In this study, we observed an upregulation of porcine IGFBP3 expression during PCV2 infection, and overexpression of IGFBP3 enhanced the expression of PCV2 Cap protein, PCV2 DNA copy number, and viral titers in PK-15 B6 cells and 3D4/21 cells. Additionally, overexpression of IGFBP3 induced an increase in the DNA damage marker γH2AX by activating the PERK/eIF2α pathway without concomitant activation of ATF4, IRE1α, and ATF6α/GRP78 pathways in PK-15 B6 cells and 3D4/21 cells. Knockdown of IGFBP3 had a reverse effect on PCV2 replication in PK-15 B6 cells and 3D4/21 cells. Furthermore, treatment with etoposide enhanced PCV2 replication while KU57788 decreased it. GSK2606414 and salubrinal limited both DNA damage and viral replication. Therefore, our findings suggest that porcine IGFBP3 promotes PCV2 replication through the PERK/eIF2α pathway-mediated induction of DNA damage in PK-15 B6 cells and 3D4/21 cells. Our study provides a basis for exploring novel antiviral strategies via the extensive understanding of the relationships between host cellular proteins and viral replication.

Examination on the Occurrence of Coinfections in Diagnostic Transmittals in Cases of Stillbirth, Mummification, Embryonic Death, and Infertility (SMEDI) Syndrome in Germany

The stillbirth, mummification, embryonic death, and infertility (SMEDI) syndrome is most commonly associated with porcine parvovirus 1 (PPV1) infections. Little is known about the occurrence of coinfections with SMEDI-associated pathogens and the associations among these pathogens. In our study, we included 40 SMEDI-affected litters from 18 different farms. In total, 158 out of 358 available fetuses from diagnostic transmittals were selected by systematic random sampling and examined for PCV2, PCV3, PPV1, and Leptospira spp. by q-PCR. Results from diagnostic materials showed the following results: in eleven farms, PCV2 was present; in nine farms, PPV1 was present; in five farms, PCV3 was present; and in two farms, Leptospira spp. was present. The detection of Leptospira spp. was significantly associated with a PCV2 coinfection (OR: 26.3; p < 0.001). PCV3 positivity resulted in a reduced probability of detecting PCV2 in the corresponding fetus (OR: 0.078; p = 0.008). Fetal maceration was associated with Leptospira spp. detection (OR: 8.6; p = 0.003), whereas mummification (p = 0.047), reduced crown-rump length (p < 0.001), and bodyweight (p = 0.001) of fetuses were significantly associated with PPV1 and PCV2 coinfection and thus, presumably, a shorter time to death after infection, indicating an enhanced negative effect on the development of fetuses with PCV2 + PPV1 coinfection.

Molecular characterization and phylogenetic analysis of porcine circovirus 2 from Kerala, India

Porcine circovirus type 2 (PCV2), the causative agent of porcine circovirus-associated diseases (PCVADs), has a worldwide distribution, and is considered as one of the most important emerging viral pathogens of economic importance. In Kerala, a total of 62 tissue samples were collected during post mortem from pigs suspected to have died of PCV2 infection. The animals exhibited symptoms like respiratory illness, gradual wasting, rough hair coat, polypnoea, dyspnoea, pallor, diarrhoea, icterus, etc. PCV2 was detected in 36 (58.06%) samples by PCR. Phylogenetic analyses of complete ORF2, and complete genome sequences were carried out and genotypes 2d, 2 h and 2b were detected. The genotype predominant in Kerala was 2d. It was observed that genotypes 2 h and 2b have been recently introduced into North Kerala as it was not detected in the region prior to 2016. Close relationship of Kerala sequences with sequences from Tamil Nadu, Uttar Pradesh and Mizoram were noticed in the phylogenetic tree and also at the amino acid level. A unique K243N mutation was observed in one of the samples. It was also noticed that the most variable amino acid position in ORF2 was 169 where the occurrence of three possible amino acids were observed. The results of the study indicate that multiple genotypes of PCV2 are prevalent in pigs in Kerala and that the percent positivity is higher than that recorded in the State previously.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-023-00814-1.

Experimental infection of high health pigs with porcine circovirus type 2 (PCV2) and Lawsonia intracellularis

Background

Porcine circovirus type 2 (PCV2) and Lawsonia intracellularis infections can cause enteritis in pigs. A Danish study showed a significantly higher probability of detecting PCV2 without concurrent L. intracellularis infection, indicating that one of these pathogens has an impact on the dynamics of the other. Therefore, a delayed co-infection model was set up, initially aiming at investigating the interaction between PCV2 and L. intracellularis in pigs challenged with PCV2 and 2 weeks later with L. intracellularis. But due to PCV2 contamination of the L. intracellularis inoculum the aim was revisited to describing the infection dynamics and pathogenesis of pigs infected with PCV2 followed by delayed simultaneous exposure to PCV2 and L. intracellularis. Twenty-four high-health piglets were divided into three groups of eight pigs (A, B, C) and inoculated at experimental day (EXD) 0 with mock (groups A and B) or PCV2 (group C), and at EXD 14 with mock (group A) or L. intracellularis/PCV2 (groups B and C). The pigs underwent daily clinical examination, and were necropsied at EXD 51–52. Furthermore, histology, immunohistochemistry, serology and PCR for PCV2 and L. intracellularis, and measurement of C-reactive protein were carried out.

Results

Group A remained negative for PCV2 and L. intracellularis. Following inoculation with L. intracellularis/PCV2, no significant differences were observed between group B and C, however pigs already infected with PCV2 (group C) showed milder clinical signs and exhibited milder intestinal lesions, less shedding of L. intracellularis and developed higher L. intracellularis antibody titers than the pigs in group B that only received the combined infection. Though the differences between group B and C were non-significant, all results pointed in the same direction, indicating that the pigs in group B were more affected by the L. intracellularis infection compared to the pigs in group C.

Conclusions

Previous exposure to PCV2 had limited impact on the subsequent exposure to a combined L. intracellularis/PCV2 inoculation. However, there was a tendency that the infection dynamics of PCV2 and development of antibodies to PCV2 and L. intracellularis were altered in pigs previously exposed to PCV2. These differences should be confirmed in further experimental trials.

Porcine Circovirus Type 2 Vaccines: Commercial Application and Research Advances

Porcine circovirus type 2 (PCV2) infection can lead to porcine circovirus-associated disease (PCVAD), causing great economic losses to the global swine industry. Conventional vaccination programs are a major measure in the prevention and control of this disease. Currently, there are 5 commercially available PCV2 vaccines in the international market and 10 kinds commercially available PCV2 vaccines in the Chinese market that confer good efficacy against this virus by alleviating clinicopathological manifestations and enhancing growth performance in pigs. In addition, diverse experimental PCV2 vaccines with protective efficiency have been developed, including attenuated chimeric, nucleic acid, subunit, multivalent, and viral-vectored vaccines. These experimental vaccines have been shown to be relatively effective in improving the efficiency of pig production and simplifying prevention procedures. Adjuvants can be used to promote vaccines with higher protective immunity. Herein, we review the application of multiple commercial vaccines over the years and research advances in experimental vaccines, which provide the possibility for the development of superior vaccines to successfully prevent and control PCV2 infection in the future.

Molecular evidence of porcine circovirus 3 infection in swine: first report in southern India

The present study examined 434 field samples including serum (n = 273), swabs from natural orifices (n = 52) and postmortem tissue samples (n = 109) from both suspected and asymptomatic swine from Andhra Pradesh, Karnataka, Kerala, Pondicherry, Tamil Nadu, and Telangana states in southern India. All the samples were processed for molecular screening of PCV3 by specific PCR assay. Overall molecular positivity rate of PCV3 was found to be 0.7% in southern India with one sample positive from each state of Tamil Nadu, Kerala and Telangana. All the three PCR positive PCV3 samples are detected from reproductive failures and were processed and propagated in PK15 cell line for virus isolation. Out of 3 samples processed, one (INDKL9PK76) PCV3 isolate could be obtained in this study and it was confirmed by specific PCR at third and fifth passage levels. Sequencing of PCV3 positive PCR amplicon (INDKL9PK76) revealed 1004 nucleotides and BLAST analysis confirmed partial sequence of the PCV3 genome. The aligned contig sequence was submitted to GenBank under the accession number of MW627201. PCV3 sequence in this study revealed 99% homology with PCV3 isolates from Europe and China. Phylogentic analysis of the PCV3 isolate-INDKL9PK76 sequence along with established PCV3 genotypes revealed clustering within PCV3 genotypes. Characterization of PCV3 (INDKL9PK76) isolate based on deduced amino acid composition of PCV3-capsid protein revealed "A" (alanine) and "R" (arginine) at 24th and 27th residues respectively confirming the incidence of PCV3a genotype. This study evidences PCV3 associated reproductive failure in domestic pigs for the first time in southern India.

Pathomorphology, immunohistochemical, and molecular detection of an atypical porcine dermatitis and nephropathy syndrome (PDNS) due to PCV-2d-2 in naturally affected grower pigs of India

Porcine circovirus type 2 (PCV-2) is of great economic significance to porcine industry worldwide. PCV-2 variants and genotypes, alternating world over, are the etiological agent of several clinical syndromes such as porcine dermatitis and nephropathy syndrome (PDNS), post-weaning multi-systemic wasting syndrome (PMWS) and others in pigs. This study is reporting an atypical manifestation of PDNS in twelve grower pigs, 3- to - 4.5 months age and either sex, died of the disease, with predominant lesions of nephropathy and no obvious clinical lesions in skin. Necropsy examination of pigs showed lesions of petechial -to- ecchymotic hemorrhages in the kidneys and in the right auricular musculature of the hearts. Microscopic lesions in H & E sections of the kidneys showed acute glomerulonephritis, interstitial nephritis, and vasculitis, but the skin morphology and architecture remained unaltered in contrast to the pathognomonic lesions of PDNS described in the literature. Other syndromic associations of PDNS in these cases included-perimyocarditis, interstitial pneumonia, depleted lymphoid tissues, tonsillitis, enteritis, and meningo-encephalitis. The lesional sites in duplicate paraffin tissue sections of kidneys, heart, lungs, spleen, lymph nodes, intestine, and brain demonstrated PCV-2 antigen in the cytoplasm of cells as highlighted by the intense immunolabeling on IHC staining. The PCV-2 positive organs reconfirmed by PCR, targeting ORF2 gene, which yielded 481bp size of products. The sequencing results of 481bp products on phylogenetic analysis showed 94% similarity with that of PCV-2 sequences in the database that grouped into PCV2d-2 genotype. The present report confirms, probably for the first time, the atypical PDNS cases due to PCV2d-2 genotype in naturally affected grower pigs of India.

Porcine Circoviruses and Herpesviruses Are Prevalent in an Austrian Game Population

During the annual hunt in a privately owned Austrian game population in fall 2019 and 2020, 64 red deer (Cervus elaphus), 5 fallow deer (Dama dama), 6 mouflon (Ovis gmelini musimon), and 95 wild boars (Sus scrofa) were shot and sampled for PCR testing. Pools of spleen, lung, and tonsillar swabs were screened for specific nucleic acids of porcine circoviruses. Wild ruminants were additionally tested for herpesviruses and pestiviruses, and wild boars were screened for pseudorabies virus (PrV) and porcine lymphotropic herpesviruses (PLHV-1-3). PCV2 was detectable in 5% (3 of 64) of red deer and 75% (71 of 95) of wild boar samples. In addition, 24 wild boar samples (25%) but none of the ruminants tested positive for PCV3 specific nucleic acids. Herpesviruses were detected in 15 (20%) ruminant samples. Sequence analyses showed the closest relationships to fallow deer herpesvirus and elk gammaherpesvirus. In wild boars, PLHV-1 was detectable in 10 (11%), PLHV-2 in 44 (46%), and PLHV-3 in 66 (69%) of animals, including 36 double and 3 triple infections. No pestiviruses were detectable in any ruminant samples, and all wild boar samples were negative in PrV-PCR. Our data demonstrate a high prevalence of PCV2 and PLHVs in an Austrian game population, confirm the presence of PCV3 in Austrian wild boars, and indicate a low risk of spillover of notifiable animal diseases into the domestic animal population.

Current Understanding of the Pathogenesis of Porcine Circovirus 3

Circoviruses are closed, circular, single-stranded DNA viruses belonging to the family Circoviridae and the genus Circovirus. To date, at least four porcine circoviruses (PCVs) have been recognized, including PCV1 to PCV4, respectively. Similar to PCV2 pathogenesis, PCV3 has been reported worldwide with myriad clinical and pathological presentations such as reproductive disorders, respiratory diseases, diarrhea etc. Current understanding of PCV3 pathogenesis is very limited since the majority of studies were mostly field observations. Interpretation of the results from such studies is not always simple. Various confounding factors affect the clinical appearance and pathological changes of the infected pigs. Recently, several experimental PCV3 infection studies have been reported, providing a better understanding of its pathogenesis. In this review, we focused on novel findings regarding PCV3 pathogenesis from both field observation and experimental infection studies. Possible factors involved in the conflicting results among the experimental infection studies are also discussed. This review article provides important insight into the current knowledge on PCV3 pathogenesis which would aid in prioritizing research in order to fill the knowledge gaps.

Characterization of porcine circovirus-like virus P1 replication and lesions in BALB/c mice

Five-week-old male BALB/c mice were inoculated intraperitoneally with a single (sP1) or multiple doses (mP1) of porcine circovirus-like virus P1 or cell culture medium. None of the mice exhibited clinical signs or gross lesions throughout the study. However, the body weights of the mP1 mice were significantly decreased, and the mice inoculated with P1 exhibited viral replication, seroconversion, and microscopic lesions. P1 nucleic acid was detected in the heart, liver, spleen, lung, bladder, testis, brain, thymus, and pancreatic tissues. Special P1 antibody was found in the P1-inoculated mice. Microscopic lesions in the sP1 and mP1 mice were characterized by interstitial pneumonia, including edema in the connective tissue around the pulmonary vessels, mild inflammatory cell infiltrate, thickened alveolar walls, myocardial necrosis, and dissolution of Purkinje cell nuclei. The results showed that the P1 virus could infect BALB/c mice. Thus, BALB/c mice may serve as models for P1 research.

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.

Haemato-biochemical alterations and oxidative stress associated with naturally occurring porcine circovirus2 infection in pigs

Porcine circovirus2 (PCV2) infection in pigs is one of the major causes of economic loss to the farmers in terms of low production, slow growth and increase post-weaning mortality rate. The effect of PCV2 infection on haemogram, serum biochemical profile and oxidant/anti-oxidant status is not well established in pigs. In the present study, haemogram, serum biochemical profile and oxidant/anti-oxidant status were assessed in pigs confirmed positive for PCV2 infections as evidenced by commercially available enzyme-linked immunosorbent assay kit (n = 151) and polymerase chain reaction (PCR) (n = 42) among a total of 306 number of pigs included in the study. Non-infected healthy pigs (n = 6) served as healthy control. The total erythrocyte count (TEC), haemoglobin (Hb), packed cell volume (PCV), total leukocyte count (TLC), differential leukocyte count (DLC) and thrombocyte count were measured. The levels of total protein, albumin, globulin, total bilirubin, direct bilirubin, blood urea nitrogen (BUN), creatinine and glucose and enzymes viz. alanine transaminase (ALT), aspartate transaminase (AST), gamma-glutamyl transferase (GGT) and alkaline phosphatase (ALP) were measured. Oxidative stress indicators such as plasma malondialdehyde (MDA) and total anti-oxidant activity (TAOA) were measured using commercially available kits. The mean values of TLC, lymphocytes and thrombocyte count were significantly (P < 0.05) low in PCV2-infected pigs. The levels of globulin, AST, GGT, BUN and creatinine were significantly increased (P < 0.05) whereas levels of albumin and glucose significantly (P < 0.05) decreased in PCV2-infected pigs. The significant increase (P < 0.05) in MDA level and significant decrease (P < 0.05) in TAOA level were noticed in PCV2-infected animals as compared with healthy control. The present study supports immunosuppression, possible multiple organ damage and oxidative stress associated with naturally occurring PCV2 infection in pigs. Timely vaccination and managemental practices can reduce PCV2 infection in farms. In spite of many research studies, there is still paucity of detailed systemic study on haemato-biochemical alteration and oxidative stress associated with PCV2 infection.

First isolation and genetic characterization of porcine circovirus type 3 using primary porcine kidney cells

Porcine circovirus type 3 (PCV3) was first detected in aborted fetuses in 2015 when sows displaying clinical signs that looked like porcine dermatitis and nephropathy syndrome died suddenly. Primary porcine kidney cells were selected for both the isolation and propagation of PCV3 strain SNUVR181115 (GenBank accession number MK503331) as these cells were permissive to PCV3 infection. PCV3 did not produce cytopathic effect on infected monolayers, therefore PCV3 infection was confirmed by in situ hybridization with a PCV3 specific DNA probe. Electron microscopy was used to analyze cell culture for the presence of virus. The intracytoplasmic inclusion bodies contained virus-like particles arranged in paracrystallline arrays on PCV3-infected primary porcine kidney cell. Virus replication peaked at 6th passage yielding titers close to 10⁶ genomic copies of PCV3 per mL. PCV3 strain SNUVR181115 isolated from primary porcine kidney cells was highly conservative and was clustered with the Korean and Chinese strains. These results demonstrated that primary porcine kidney cells are useful for PCV3 isolation and replication.

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.

Protective humoral immunity in guinea pigs induced by PCV2 virus-like particles displaying the B cell linear epitope (228QQITDA233) of PPV1

Although PCV2 infections generally cause mild disease in pigs, concurrent co-infections with other pathogens can damage the immune system and cause more severe diseases, collectively termed porcine circovirus associated diseases (PCVAD). Involvement of porcine parvovirus (PPV, a common cause of reproductive failure in naïve dams) in PCVAD caused by PCV2, has been reported. As this co-infection can be difficult to eliminate, there is a critical need to develop an effective vaccine to protect against PPV or synergistic effects of PCV2 and PPV under field conditions. In this study, we designed chimeric PCV2 virus-like particles (cVLPs) displaying a B-cell epitope derived from PPV1 structural protein around the surface of the 2-fold axes of PCV2 VLPs, based on 3D-structure analysis of the PCV2 capsid. The cVLPs were successfully prepared, verified by transmission electron microscopy and chromatography, with robust antibody titers against PCV2 and PPV1 produced in mice and guinea pigs. In addition, in guinea pigs challenged with 10⁶ TCID₅₀ PCV2, cVLPs conferred more effective immune protection (based on viral load) than a commercial PCV2 vaccine. Finally, antibody responses and immune protection against PPV were also evaluated. In guinea pigs vaccinated with cVLPs, although PPV antibodies detected by a hemagglutination inhibition (HI) assay appeared later after vaccination in the PCV2 cVLPs group than in the commercial PPV vaccine group, there were fewer PPV genomic DNA copies in the PCV2 cVLPs group than in a PBS group. In conclusion, guinea pigs vaccinated with cVLPs developed effective protective immunity against PCV2 challenge, with some protective immunity against PPV. This study provided valuable research data to pursue molecular design of chimeric epitopes PCV2 VLPs.

The emergence of porcine circovirus 2 infections in the Northeastern part of India: A retrospective study from 2011 to 2017

Porcine circovirus (PCV) infection has emerged as an alarming threat to the pig population of India, especially in the Northeastern region (NER) over the last 10 years. The present study is a comprehensive report of the seroepidemiology of PCV2 and its incidences in the pig population from organized and unorganized farms of the entire NER of India from 2011 to 2017. A total of 5697 serum samples were screened by ELISA and the mean positivity of PCV2 antibodies in suspected sera was 31.27%. A total of 22 confirmed cases of PCV2 infection were recorded during the years 2014-2017. Seroprevalence of PCV2 infection in sows causing reproductive disorders in NER suggested its higher incidence in organized farms (65.7%) as compared to unorganized farms (17.6%). A detailed pathological and histopathological examination of the tissue samples collected from the affected animals indicated the presence of PCV2. Molecular characterization and phylogenetic analysis of four PCV2 isolates depicted the circulation of PCV2d genotype in the states of Meghalaya and Assam.

Duplex nested reverse transcriptase polymerase chain reaction for simultaneous detection of type 2 porcine reproductive and respiratory syndrome virus and porcine circovirus type 2 from tissue samples

There are high levels of co-incidence of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) in porcine tissue. This study established a duplex nested reverse transcriptase polymerase chain reaction (RT-PCR) method that targets the genomic RNA of type 2 PRRSV and the mRNA of PCV2 in infected tissues. The method amplified discriminative bands of 347 bp and 265 bp specific for type 2 PRRSV and PCV2, respectively. The limits of detection of the duplex nested RT-PCR were 10^1.5 TCID₅₀/mL for type 2 PRRSV and 10² infected cells/mL for PCV2. The kappa statistic, which measures agreement between methods, was 0.867, indicating a good level of agreement. This RNA-based duplex RT-PCR approach can be another way to detect type 2 PRRSV and PCV2 simultaneously and with improved convenience.

Identification and functional analysis of the novel ORF6 protein of porcine circovirus type 2 in vitro

In the present study, the function of a novel ORF6 gene in the PCV2 genome was determined and functionally analyzed in vitro. ORF6 expression was demonstrated by indirect immunofluorescence in PCV2-infected cells. The antibody against ORF6 was detected in PCV2-infected pigs. The start codon of ORF6 was mutated and an infectious clone was used to create an ORF6-deficient mutant virus. Viral DNA replication curves and immunofluorescence analysis indicated that ORF6 is unnecessary for viral replication and ORF6 deletion reduces viral DNA replication in PK-15 cells. The activities of caspases 3 and 8 in ORF6-deficient virus-infected cells were significantly different from those in wild-type virus-infected cells. The ORF6 protein can increase the expression of IFN-β, TNF-α, IL-1b, IL-10, and IL-12p40. These results demonstrated that the newly discovered ORF6 protein may be involved in caspases regulation and the expression of multiple cytokines in PCV2-infected cells. The functions of this gene in viral pathogenesis remain to be further elucidated.

Granulomatous Necrotizing Myositis in Swine Affected by Porcine Circovirus Disease

Porcine circovirus type 2 (PCV2) is associated with multiple clinical syndromes in pigs, known as porcine circovirus diseases. This work describes an outbreak of porcine circovirus diseases with severe lesions affecting the skeletal muscle. Ninety-two pigs had apathy, weight loss, and diarrhea over a clinical course of 7 to 10 days. Approximately 30 of the pigs had stiff gait, muscle weakness, hind limb paresis, and recumbency. Twelve of the 92 pigs were necropsied, and 4 had pale discoloration of skeletal muscles with microscopic lesions of granulomatous necrotizing myositis. Immunohistochemistry of skeletal muscle showed that PCV2 antigen was located primarily in the cytoplasm and nuclei of macrophages, lymphocytes, and multinucleated giant cells, with a lower amount in the cytoplasm of endothelial cells, necrotic fibers, and satellite cells. Affected muscle samples were polymerase chain reaction-positive for PCV2 and the amplicon exhibited 99% identity with sequences belonging to the PCV2b genotype. Locomotor clinical signs and granulomatous necrotizing myositis should be considered as another expression of PCV2 infection in pigs.

Novel effects of identified SNPs within the porcine Pregnancy-Associated Glycoprotein gene family (pPAGs) on the major reproductive traits in Hirschmann hybrid-line sows

This is the first study describing identification of SNPs within the multiple and polymorphic Pregnancy-Associated Glycoprotein gene family (PAGs) in the genome of the domestic pig (pPAGs). We identified pPAG-like (pPAG-L) genotypes in primiparous and multiparous farmed hybrid-line JSR Hirschmann (Hrn) sows (N=159), in which various novel associations with their phenotypes for the major reproductive traits have been discovered. Genomic DNA templates were isolated from the blood and different pPAG-L primers were used to amplify various regions by PCR. Electrophoretically-separated amplicons were selected, purified and sequenced. All identified SNPs were verified for possible pPAG2-L genotype associations with the major reproductive traits. In total, 196 SNPs were identified within the entire structure of the pPAG2-Ls, encompassing 9 exons and 8 (A-H) introns, resembling all aspartic proteinases. It was discovered that among all SNPs, one diplotype localized in exon 6 (657C>T/749G>C; pPAG2 ORF cDNA numbering; L34361) caused amino acid substitutions (Asp²²⁰→Asn and Ser²⁵⁰→Thr) in the polypeptide precursors and was associated with an increase in the number of live-born piglets (P≤0.05) in Hrn sows. In turn, co-localized SNP (504g>a; KF537535 numbering) in the intron F of the pPAG2-Ls, but only in the homozygotic genotype (gg), was associated with an increased number of live-born (P≤0.01) and weaned (P≤0.05) piglets in the Hrn sows. These results qualify the pPAG2-Ls as candidate genes of the main QTLs. The novel pPAG SNP profiles provide the basis for a diagnostic genotyping test required for early pre-selection of female/male piglets, presumably mainly useful in various breeding herds.

Depletion of follicular dendritic cells in tonsils collected from PMWS-affected pigs

Post-weaning multisystemic wasting syndrome (PMWS) is a relevant, worldwide disease caused by porcine circovirus type 2 (PCV2). Microscopically, PMWS is mainly characterized by lymphocytic depletion, macrophage infiltration and syncytia in lymphoid tissues. Some data suggest that follicular dendritic cells (FDCs) could be infected by PCV2, thus likely playing a role in the pathogenesis of PMWS. The present paper aims at assessing, qualitatively and quantitatively, the FDCs' network in the soft palate tonsils of clinically healthy and PMWS-affected pigs. Consecutive tissue sections were tested by immunohistochemistry to detect PCV2, FDCs and macrophages. FDCs and PCV2 antigens were quantitatively assessed by means of the Image J software and results submitted to statistical analysis. Our data demonstrated that FDCs are significantly reduced in PMWS-affected pigs compared with healthy pigs and that FDCs' depletion should be considered among microscopic features of PMWS. It is reasonable to hypothesize that depletion of FDCs further compromises the immune response and enhances the occurrence and the severity of secondary infections, which are relevant for the clinical manifestation of PMWS.

Potentiation of Porcine Circovirus 2-induced Postweaning Multisystemic Wasting Syndrome by Porcine Parvovirus Is Associated with Excessive Production of Tumor Necrosis Factor-α

This study investigated the potentiation of porcine circovirus 2 (PCV2)-induced postweaning multisystemic wasting syndrome by porcine parvovirus (PPV) and found it was associated with excessive production of tumor necrosis factor-α (TNF-α). Colostrum-deprived conventional pigs were inoculated intranasally with PCV2 or PPV alone or in combination (PCV2 and PPV). In vitro assay of TNF-α, obtained from alveolar macrophages coinfected with PCV2 and PPV, showed a significant increase in TNF-α compared to single infection of macrophages with either PCV2 or PPV alone ( P < 0.05). All pigs inoculated with PCV2 and PPV developed severe postweaning wasting syndrome, whereas clinical signs (e.g., weight loss) were present but perhaps less severe in either PCV2- or PPV-inoculated pigs. Compared to the pigs inoculated with PCV2 or PPV alone, pigs inoculated dually with PCV2 and PPV showed significantly ( P < 0.05) increased levels of TNF-α. Levels of TNF-α in the sera were reversely correlated with the body weight in pigs experimentally infected with dual inoculation of PCV2 and PPV ( rs = -0.92, P < 0.001). These data suggest that a potentiation of PPV in PCV2-induced PMWS is associated with the excessive production of TNF-α.

Features of Porcine Circovirus-2 Disease: Correlations between Lesions, Amount and Distribution of Virus, and Clinical Outcome

Tissue sets from 36 snatch-farrowed colostrum-deprived (SF/CD) and 71 Caesarian-derived gnotobiotic swine infected with porcine circovirus type 2 (PCV-2) as neonates were examined and scored for the types and tissue distribution of histologic lesions associated with this viral infection. The occurrence and severity of these lesions were correlated with qualitative and quantitative determinations of viral burden in tissues by immunohistochemistry (IHC) and tissue titrations for infectious virus, respectively. These measures were, in turn, related to 1 of 3 categories of clinical disease expressed in PCV-2–infected swine as subclinical infection, preclinical postweaning multisystemic wasting syndrome (PMWS), and clinically evident PMWS, respectively. Statistically significant ( P < 0.05 to 0.001) associations between both measures of viral burden, the severity of histologic lesions and the stage of disease were obtained. Discrimination between and among categories of disease was best accomplished by a combination of IHC and histopathology. The results of this study confirm that viral burden in PCV-2–infected tissues, specifically lymphoid tissues and liver, directly correlate with severity of clinical disease expression in PCV-2 infected swine.

Nested Polymerase Chain Reaction Detection and Duration of Porcine Circovirus Type 2 in Semen with Sperm Morphological Analysis from Naturally Infected Boars

A nested polymerase chain reaction (nPCR) protocol was applied to porcine semen to demonstrate the porcine circovirus type 2 (PCV2) shedding patterns and duration in naturally infected boars. Sperm morphology analysis was performed on a subset of samples to determine if the presence of PCV2 DNA in semen was associated with reduced semen quality. Semen was collected serially from 43 boars representing 6 breeds, aged 33.9 to 149.3 weeks. Of the 903 semen samples collected, 30 samples (3.3%) were positive for PCV2 DNA by nPCR from 13 boars. Boars shedding PCV2 DNA in semen ranged between 35.9 and 71.0 weeks of age, and shedding occurred during a period of up to 27.3 weeks. A semen nPCR test was 2.6 times more likely to be positive when collected from pigs that were ≤52 weeks of age, and 3.0 times more likely to be positive when collected from pigs that were ≤26 weeks from time of entry into the stud main unit (generalized estimating equations: P = 0.02; 95% confidence interval [CI] of the odds ratio 1.2 to 5.5, and P = 0.01; 95% CI of the odds ratio 1.3 to 6.9, respectively). These results demonstrate a sporadic and long-term shedding pattern of PCV2 DNA in semen from naturally infected boars. PCV2 DNA in semen does not appear to have detrimental effects on sperm morphology; however, boar age and, possibly, breed may contribute to the persistence of PCV2-shedding in semen.

Canine Circovirus 1 (CaCV-1) and Canine Parvovirus 2 (CPV-2): Recurrent Dual Infections in a Papillon Breeding Colony

Recurrent outbreaks of sudden death and bloody diarrhea were reported in March 2013 and February 2014 in a breeding colony of Papillon dogs. During the first outbreak, 1 adult dog and 2 eight-month-old puppies died. During the second outbreak, 2 ten-week-old puppies died. One puppy from the first outbreak and 2 puppies from the second outbreak were examined at necropsy. Histologically, all 3 puppies had severe segmental crypt necrosis of the small intestine and marked lymphoid follicle depletion in the spleen and Peyer's patches. Real-time (RT) polymerase chain reaction (PCR) demonstrated abundant canine parvovirus (CPV-2) DNA (Ct<15) in the affected small intestine, and immunohistochemistry detected large amounts of CPV-2 antigen in intestinal crypt epithelium and Kupffer cells but few positive macrophages in lymphoid organs. All puppies had marked sinusoidal histiocytosis and multifocal granulomatous inflammation in mesenteric lymph nodes and spleen, prompting additional RT-PCR testing for canine circovirus 1 (CaCV-1). Very high levels of CaCV-1 DNA (Ct<13) were detected in small intestine, lymph nodes, and spleen. In situ hybridization for CaCV-1 detected rare positive nuclei of regenerating crypt epithelium but abundant amounts of CaCV-1 nucleic acid in the cytoplasm and nuclei of histiocytes in all lymphoid tissues, including granulomatous inflammatory foci and hepatic Kupffer cells. Significant levels of CaCV-1 DNA were detected in blood and serum (Ct as low as 13) but not feces from 3 surviving dogs at 2 months or 1 year after the outbreak, respectively. We hypothesize that CPV-2 infection predisposed dogs to CaCV-1 infection and ultimately resulted in more severe clinical disease.

Vaccination with a Porcine Reproductive and Respiratory Syndrome (PRRS) Modified Live Virus Vaccine Followed by Challenge with PRRS Virus and Porcine Circovirus Type 2 (PCV2) Protects against PRRS but Enhances PCV2 Replication and Pathogenesis Compared to Results for Nonvaccinated Cochallenged Controls

Coinfections involving porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) contribute to a group of disease syndromes known as porcine circovirus-associated disease (PCVAD). Presumably, PRRSV infection enhances PCV2 replication as a result of modulation of host immunity. The purpose of this study was to evaluate PCV2 replication and pathogenesis in pigs vaccinated with a PRRS modified live virus (MLV) vaccine and subsequently challenged with a combination of PRRSV and PCV2. During the early postchallenge period, the number of pigs with PRRSV-associated clinical signs was decreased, and average daily gain (ADG) was increased, in the vaccinated group, demonstrating the protective effect of PRRS vaccination. However, during the later postchallenge period, more pigs in the vaccinated group showed increased PCV2 viremia, decreased ADG, increased PCVAD clinical signs, and increased mortality. In this disease model, the early benefits of PRRSV vaccination were outweighed by the later amplification of PCVAD.

Genetic identification of Entamoeba polecki subtype 3 from pigs in Japan and characterisation of its pathogenic role in ulcerative colitis

To date, three Entamoeba spp. (E. suis, zoonotic E. polecki and E. histolytica) have been identified in pigs, but their pathogenicity and molecular classification have not been fully determined. Examination and pathological analysis of pigs (n=3) with diarrhoea was conducted and revealed the presence of Entamoeba organisms. We performed a genetic analysis of the isolate using the small-subunit ribosomal RNA (SSU rRNA) gene region to identify the species. A severe ulcerative colitis was observed histopathologically with inflammatory cells, including macrophages and neutrophils, infiltrating the mucous membranes of the cecum and colon. Many Entamoeba trophozoites were found at the erosion site or at ulcerative lesions. Pathogenic viruses or bacteria were not detected. The SSU rRNA sequence of the Entamoeba isolate was found to be completely homologous to that of E. polecki subtype 3.

Coincidental detection of genomes of porcine parvoviruses and porcine circovirus type 2 infecting pigs in Japan

The infection status of 15 viruses in 120 pigs aged about 6 months was investigated based on tonsil specimens collected from a slaughterhouse. Only 5 species of porcine parvoviruses and porcine circovirus type 2 (PCV2) were detected at high frequencies; 67% for porcine parvovirus (PPV) (PPV-Kr or -NADL2 as the new abbreviation), 58% for PPV2 (CnP-PARV4), 39% for PPV3 (P-PARV4), 33% for PPV4 (PPV4), 55% for PBo-likeV (PBoV7) and 80% for PCV2. A phylogenetic analysis of PPV3 suggested that Japanese PPV3s showed a slight variation, and possibly, there were farms harboring homogeneous or heterogeneous PPV3s. Statistical analyses indicated that the detection of PCV2 was significantly coincidental with each detection of PPV, PPV2 and PPV3, and PPV and PPV4 were also coincidentally detected. The concurrent infection with PCV2 and porcine parvoviruses in the subclinically infected pigs may resemble the infection status of pigs with the clinical manifestations of porcine circovirus associated disease which occurs in 3–5 months old pigs and is thought to be primarily caused by the PCV2 infection.

Porcine cytomegalovirus infection is not associated to the occurrence of post-weaning multisystemic wasting syndrome

Porcine cytomegalovirus (PCMV) is a Betaherpesvirus that causes lifelong latent infections in swine; occasionally, it may be associated with inclusion body rhinitis in piglets and reproductive disorders in pregnant sows. Post‐weaning multisystemic wasting syndrome (PMWS) a condition where porcine circovirus type 2 (PCV2) infection is necessary – though not sufficient – to trigger disease, has become one of the major health problems to the porcine productive chain. Despite the high expected prevalence of both PCMV and PCV2 in swine‐raising farms, no links between PCMV and PMWS have been investigated so far. In view of that, the present study was conducted to search for relations between PCMV infections and the occurrence of PMWS. Spleen and sera of PMWS‐affected and non‐PWMS‐affected animals were examined. In PMWS‐affected animals, PCMV DNA was detected in 88.4% of the spleen samples and 7.6% of the sera, whereas in non‐PMWS‐affected pigs, PCMV DNA was detected in 72.7% of the spleens and 10% of sera. Such differences were not statistically significant. These findings showed despite the high prevalence of PCMV infections in the swine population examined, no positive or negative association could be inferred from the presence of PCMV DNA and the occurrence of PMWS.

Porcine circovirus: a historical perspective

Porcine circoviruses (PCVs) belong to the genus Circovirus and the family Circoviridae, and they are the smallest known viruses that replicate autonomously in mammalian cells. They are nonenveloped, and they have characteristic single-stranded, negative-sense, circular DNA. Two types of divergent PCVs are recognized: PCV1 and PCV2. About 20 years ago, PCV2 began to emerge as a major pathogen of swine around the world, leading to burgeoning knowledge about the virus and porcine circovirus-associated diseases. However, much of the history of its discovery, including the controversy related to its importance, is not recorded. This review examines current issues related to the biology of PCV2 in the context of the original studies related to determining its causal association with disease and to the evolving understanding of the complex pathogenesis of PCV2 infections.

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.

Identification of recently described porcine parvoviruses in archived North American samples from 1996 and association with porcine circovirus associated disease

The association of porcine circovirus (PCV) type 2 and porcine parvovirus (PPV) type 1 as a cause of porcine circovirus associated disease (PCVAD) is well established. The objective of this study was to investigate the prevalence rates of classical PPV1 and recently recognized PPV2-5 in serum and lung samples from pigs and farms with known PCV2 status. A total of 586 serum samples and 164 lung homogenates collected from 1996 to 2013 in the USA and Canada were utilized. All samples were tested for PPV1-5 and PCV2. PCV2 was detected in 27.7% (162/586) and PPV in 48.8% (286/586) of the serum samples, whereas 78.7% (129/164) of the lung tissues were positive for PCV2 and 56.7% (93/164) were positive for PPV. Overall, PPV2 had the highest prevalence rates in sera (35.2%) and tissues (42.7%). Concurrent infection of PCV2 and PPV occurred in 14.3% (84/586) of the serum samples and in 49.4% (81/164) of the tissue samples. Moreover, the prevalence of PPV1 or PPV2 DNA was significantly higher in tissues containing high amounts of PCV2 DNA compared to non-PCVAD cases. The frequency of concurrent PPV/PCV2 infection was higher for PCVAD herds compared to negative or subclinically infected herds. PPV2, PPV3 and PPV4 were all identified in samples collected in 1998 and PPV5 was first identified in 2006. The obtained findings indicate that similar to PCV2, PPVs are widespread in North American pigs. Nevertheless, diagnostic investigations into PCVAD cases should give more consideration to the role of PPV1 and PPV2 as contributing cofactors.

A multiplex RT-PCR assay for rapid and differential diagnosis of four porcine diarrhea associated viruses in field samples from pig farms in East China from 2010 to 2012

Since October 2010, clinical outbreaks of diarrhea in suckling piglets have reemerged in pig-producing areas of China, causing an acute increase in the morbidity and mortality in young piglets. Four viruses, porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), porcine group A rotaviruses (GAR), and porcine circovirus 2 (PCV2), are the major causative agents of enteric disease in piglets. A novel multiplex reverse transcription-polymerase chain reaction (mRT-PCR) was developed for simultaneous detection of the four viruses in field samples from piglets. A mixture of four previously published pairs of primers were used for amplification of viral gene, yielding four different amplicons with sizes of 481 bp for PCV2, 651 bp for PEDV, 859 bp for TGEV, and 309 bp for GAR, respectively. The sensitivity of the mRT-PCR using plasmids containing the specific viral target fragments was 2.17 × 10(3), 2.1 × 10(3), 1.74 × 10(4) and 1.26 × 10(4)copies for the four viruses, respectively. A total of 378 field samples were collected from suckling piglets with diarrhea in East China from October 2010 to December 2012, and detected by mRT-PCR. The PEDV-positive rates of the three years were 69.2%, 62.8% and 54.9%, respectively, suggesting that PEDV was a major pathogen in these diarrheal outbreaks. Taken together, all data indicated that this mRT-PCR assay was a simple, rapid, sensitive, and cost-effective detection method for clinical diagnosis of mixed infections of porcine diarrhea associated viruses.

Cellular pathogenesis of porcine circovirus type 2 infection

Porcine circovirus associated disease (PCVAD) and the associated histological lesions are thought to appear due to an increase in the amount of porcine circovirus type 2 (PCV2) present in an infected animal. However, examination of the cellular and molecular pathogenesis of PCVAD is complicated by the lack of a consistent cell culture model that replicates the animal phenotypes of persistent, asymptomatic infection, and acute, pathological disease typified by lymphocyte depletion. The porcine fetal retina cell line, VR1BL, shows a high permissiveness to PCV2 infection, 40 times higher than the alternative PK15 culture model, allowing for high titer viral production, with PCV2b growth higher than PCV2a growth. Cytopathic effect due to apoptosis is observed after challenge with high amounts of PCV2, but at low levels, infection is maintained in passaged cells. Thus, VR1BL cells may be used as a model system to examine both acute viral pathogenesis and cellular innate defense, as well as persistent PCV2 infection.

Experimental airborne transmission of porcine postweaning multisystemic wasting syndrome

The objective of these studies was to investigate if porcine postweaning multisystemic wasting syndrome (PMWS) could be induced in healthy pigs following contact with air from pigs with clinical signs of PMWS. The pigs were housed in different units. Either 31 (study I) or 25 (study II) pigs with clinical symptoms of PMWS from a PMWS-affected herd and 25 healthy pigs from a PMWS-free, but PCV2-positive, herd were housed in unit A. Fifty pigs from a PMWS-free herd were housed in unit B, which were connected by pipes to unit A. In unit C, 30 pigs from a PMWS-free herd were housed as controls. In study II, the pigs in units A and B from the PMWS-free herd developed clinical signs of PMWS 2-3 weeks after arrival. PMWS was confirmed at necropsy and the diseased pigs had increased PCV2 load and increased antibody titers against PCV2 in serum that coincided with the development of clinical signs typical of PMWS. Sequence analysis revealed that the PCV2 isolate belonged to genotype 2b. In conclusion, the present study showed that PMWS can be induced in pigs from a PMWS-free herd by airborne contact with pigs from a PMWS-affected herd.

Porcine circovirus type 2 (PCV2): pathogenesis and interaction with the immune system

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated disease (PCVAD). The virus preferentially targets the lymphoid tissues, which leads to lymphoid depletion and immunosuppression in pigs. The disease is exacerbated by immunostimulation or concurrent infections with other pathogens. PCV2 resides in certain immune cells, such as macrophage and dendritic cells, and modulates their functions. Upregulation of IL-10 and proinflammatory cytokines in infected pigs may contribute to pathogenesis. Pig genetics influence host susceptibility to PCV2, but the viral genetic determinants for virulence remain unknown. PCV2 DNA and proteins interact with various cellular genes that control immune responses to regulate virus replication and pathogenesis. Both neutralizing antibodies and cell-mediated immunity are important immunological correlates of protection. Despite the availability of effective vaccines, variant strains of PCV2 continue to emerge. Although tremendous progress has been made toward understanding PCV2 pathogenesis and immune interactions, many important questions remain.

Detection of Torque teno sus virus 1 and 2 in tissues from stillborn piglets delivered by sows via natural farrowing

We detected Torque teno sus virus1 and 2 (TTSuV1 and TTSuV2) in tissue samples from 18 stillborn piglets using nested polymerase chain reaction. The detection rates of TTSuV1 and TTSuV2 were 78% and 50%, respectively, with 83% of the stillborn piglets positive for TTSuV1 or TTSuV2. TTSuV1 was detected highest in the liver (72%) followed by heart (56%), spleen (38%) and tonsils (38%) while TTSuV2 was detected highest in the tonsils (38%) followed by liver (33%), spleen (25%), and heart (17%). These results indicate that TTSuVs are commonly present but not equally distributed among the tissues of stillborn piglets.

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.