Distinction between porcine circovirus type 2 enteritis and porcine proliferative enteropathy caused by Lawsonia intracellularis

The presence of porcine circovirus type 2 (PCV2) was studied immunohistochemically in formalin-fixed, paraffin wax-embedded samples of intestinal tissue from 80 pigs with a clinical history suggestive of Lawsonia intracellularis-associated diarrhoea. Histopathologically, enteritis of varying intensity was diagnosed in 64 of the pigs. Of these 64 animals, 34 (18%) were infected with both PCV2 and L. intracellularis. Of the remaining 30 cases of enteritis, 23 (77%) were attributed to PCV2 infection alone. The PCV2-associated enteritis cases showed necrotizing ileitis and colitis, indistinguishable macroscopically from proliferative enteritis (PE) due to L. intracellularis. Histopathologically, L. intracellularis-positive intestines showed adenomatous proliferation of crypt enterocytes, whereas PCV2 enteritis was characterized by histiocytosis of varying intensity, with PCV2-positive cells in the submucosa, lamina propria and crypt epithelium, as well as in the lymphoid tissue of the ileum and colon. Multinucleated giant cells, however, were seen in both infections. PCV2 was about three times more likely to be detected in L. intracellularis-negative than in L. intracellularis-positive samples (P<0.001). There was no association between PCV2 and other intestinal bacterial pathogens. The study demonstrated that PCV2 enteritis should be borne in mind in the differential diagnosis of L. intracellularis infection in pigs aged 2-4 months with a clinical history of diarrhoea.     

Comparison of Four Commercial One-Dose Porcine Circovirus Type 2 (PCV2) Vaccines Administered to Pigs Challenged with PCV2 and Porcine Reproductive and Respiratory Syndrome Virus at 17 Weeks Postvaccination To Control Porcine Respiratory Disease Complex under Korean Field Conditions

Under Korean field conditions, coinfection with porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) is most commonly observed in porcine respiratory disease complex (PRDC). Despite the wide use of PCV2 vaccination, PRDC remains a serious respiratory problem. Thus, the objective of this study was to determine and compare the efficacy of 4 one-dose PCV2 vaccines on 3-week-old pigs with an experimental PCV2-PRRSV challenge at 17 weeks postvaccination. Regardless of which commercial PCV2 vaccine was used, the vaccination of piglets at 3 weeks of age was efficacious against cochallenge of PCV2 and PRRSV, on the basis of growth performance and PCV2-associated lesions. However, the inactivated chimeric PCV1-2 and the PCV2 vaccines induced higher PCV2-specific neutralizing antibody (NA) titers and PCV2-specific gamma interferon-secreting cells and lower PCV2 viremia levels than the two PCV2 subunit vaccines. The vaccination of piglets against PCV2 at 3 weeks of age was effective in reducing PCV2 viremia and PCV2-associated lesions during the finishing period, which is an age at which pigs are frequently affected by PRDC caused by coinfection with PCV2 and PRRSV under Korean field conditions.     

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.     

Porcine circovirus type 2 and its associated diseases in Korea

This review describes the characterization of porcine circovirus type 2 (PCV2), the field situation of porcine circovirus-associated disease (PCVAD) and the PCV2 vaccine in Korea. PCVAD has been considered the most devastating disease in Korean livestock history since its first outbreak in 1999. Postweaning multisystemic wasting syndrome (PMWS) and porcine respiratory disease complex (PRDC) are the most common clinical forms of PCVAD. Interestingly, only PCV2b strains have been isolated from pigs with PMWS since 2005, but only PCV2a strains were isolated from pigs with PMWS in 2000 to 2001. Clinically, PMWS is divided into two stages: early and late. Early PMWS primarily occurs in pigs between 4 and 8 weeks of age. This form is a typical presentation of PMWS and is characterized clinically by wasting, decreased weight gain, enlarged lymph nodes, and dyspnea. Late PMWS primarily occurs in pigs between 8 and 12 weeks of age. The main clinical manifestation is diarrhea, which is often accompanied by salmonellosis coinfection. In recent years, the PCVAD disease pattern has slightly changed. The occurrence of PMWS has decreased while PRDC cases are increasing in frequency.     

Experimental transmission of porcine circovirus type 2 (PCV2) in weaned pigs: a sequential study

Weaned specific pathogen-free pigs were inoculated intranasally with porcine circovirus type 2 (PCV2) and killed in groups of two or three animals at 6, 13, 20, 27 and 34 days post-inoculation (dpi), together with appropriate uninfected controls, for examination by histopathological, immunohistochemical (immunogold silver staining; IGSS), polymerase chain reaction (PCR) and viral isolation techniques. Serum samples were also collected for detection of antibodies. No major clinical signs were observed in infected pigs, and gross lesions were essentially limited to the lungs and lymph nodes of some of the animals. Histologically, no lesions were seen at 6 dpi, but bronchointerstitial pneumonia was invariably noted from 13 dpi onwards. Granulomatous inflammation, with or without intracytoplasmic inclusions, was present in lymphoid tissues (e.g. lymph nodes, thymus, spleen and tonsil) from day 20 onwards, being most severe at days 20 and 27 dpi. Liver inflammation was present at days 13, 20 and 27 dpi. Virus was demonstrated in the tissues by isolation and PCR methods throughout the experiment. PCV2 antigens were detected by IGSS in bronchial and bronchiolar epithelial cells, in mononuclear cells and multinucleated giant cells within inflammatory lesions, and in mononuclear cells of apparently normal tissues (e.glamina propria of the small intestine and the bronchus-associated lymphoid tissue). The lesions were consistent with those of postweaning multisystemic wasting syndrome (PMWS), although not all previously reported PMWS lesions were seen. PCV2 antibodies were detected in infected pigs from day 13 onwards. The results demonstrated widespread distribution of PCV2 after infection and persistence of the virus in vivo for at least 34 days. It would appear that PCV2 can induce PMWS lesions in weaned pigs in the absence of porcine parvovirus and other common swine pathogens.     

Effect of Porcine Circovirus Type 2 (PCV2) Vaccination of the Dam on PCV2 Replication In Utero

The aims of this study were to determine if porcine circovirus type 2 (PCV2) vaccination of the dam is effective in preventing fetal PCV2 infection and reproductive failure. Twelve pregnant, PCV2-naïve sows were randomly divided into four groups, with three sows in each group. Group 1 sows served as noninoculated, nonvaccinated negative controls, group 2 sows were vaccinated with a commercially available PCV2 vaccine at 28 days of gestation and were not inoculated, group 3 sows were vaccinated at 28 days of gestation and inoculated with PCV2b at 56 days of gestation, and group 4 sows were inoculated with PCV2b but were not vaccinated. Serum samples from all sows were collected weekly throughout the gestation period, and sows were allowed to farrow naturally. At parturition, sow colostrum samples, presuckle serum samples, and tissues from the piglets were collected. Reproductive failure was not observed under the study conditions. PCV2 vaccination induced PCV2-specific immunoglobulin G and serum neutralizing antibodies in sows from groups 2 and 3 and prevented detectable PCV2 viremia in the dams after challenge. In group 3, PCV2 DNA was detected in colostrum samples, fetuses, and live-born pigs; however, microscopic lesions and PCV2-specific antigen were not present in any of the fetuses in this group. The results from this study indicate that vertical transmission of PCV2 can occur in PCV2-vaccinated dams.Porcine circovirus type 2 (PCV2) is a nonenveloped, single-stranded, circular DNA virus of approximately 1.7 kb and is classified in the Circoviridae family, in the genus Circovirus (38). PCV2 has three currently recognized genotypes, namely, PCV2a, PCV2b, and PCV2c (4, 26). Multiple disease entities are recognized with PCV2 infection in swine and include pneumonia, diarrhea, wasting, and reproductive failure (26). PCV-associated disease (PCVAD) is used to describe the multisystemic disease manifestations related to PCV2 infection.PCV2 was first described for growing high-health-status pigs in Canada (9) and was later found to be associated with reproductive disease in mature animals (24, 39). PCV2-associated reproductive failure was first reported in Canada. Clinically, the cases were characterized by late-term abortions, decreased numbers of viable piglets, and increased numbers of stillborns and mummified fetuses (24, 39). Gross lesions of PCV2-associated fetal infection included dilated cardiomyopathy, pulmonary edema, hepatomegaly, and ascites. The most consistent microscopic changes associated with PCV2 infection of fetuses include myocardial degeneration, necrosis, fibrosis, and nonsuppurative myocarditis (39). These changes are due to an apparent PCV2 tropism for fetal myocardiocytes (34). However, this tropism diminishes in late gestation, and increased levels of PCV2 DNA can be detected in lymphoid tissues (33). In addition, PCV2 was found to be capable of crossing the placenta and causing fetal infection in PCV2-negative sows during viremia after intranasal inoculation (29). It has been demonstrated that PCV2 inoculation of sows 3 weeks before parturition can result in lethargy, abortion, and delivery of stillborn piglets as early as 7 days postinoculation (29).During 2004 and 2005, PCVAD in growing pigs spread rapidly throughout North America, resulting in severe disease characterized by high morbidity, high mortality, and decreased growth efficiencies. Molecular characterization of the PCV2 strains involved in these outbreaks identified PCV2b, which had not been reported previously in North America (2). Thereafter, multiple PCV2 vaccines became available for disease prevention. However, an approved sow vaccine to protect against PCV2-associated reproductive failure is not currently available in the United States. The objective of this study was to determine if PCV2 vaccination of the dam is effective in preventing fetal PCV2 infection and reproductive losses.     

Reproduction of lesions of postweaning multisystemic wasting syndrome by infection of conventional pigs with porcine circovirus type 2 alone or in combination with porcine parvovirus

Post-weaning multisystemic wasting syndrome (PMWS) has recently emerged as an important disease of pigs in North America, Europe and Asia. Porcine circovirus type 2 (PCV2) and porcine parvovirus (PPV) have been isolated from affected pigs. To investigate the pathogenicity of these isolates, groups of colostrum-deprived conventional pigs were inoculated with PCV2 alone (n=4), PPV alone (n=3) or dually with PCV2 and PPV (n=7) and examined post mortem between 21 and 26 days post-infection (dpi). Two control pigs were inoculated with an uninfected cell culture lysate. All pigs that received both viruses became dull at approximately 10-12 dpi and six of these animals subsequently developed jaundice. Hepatomegaly and enlarged kidneys were prominent post-mortem findings in these animals. Histopathological examination revealed severe macrophage infiltration, syncytia formation and numerous cytoplasmic and nuclear amphophilic inclusion bodies in lymphoid tissues. Granulomatous lesions were apparent in liver, lung, kidney, pancreas, myocardium, intestines, testis, brain and salivary, thyroid and adrenal glands. Abundant PCV2 antigen was detected in affected tissues. Only one of the four pigs inoculated with PCV2 alone developed clinical signs, but they all had histopathological lesions which, although less severe, were similar to those in the dually infected animals. The control pigs and those infected with PPV alone remained clinically normal and did not have gross lesions. The only histopathological lesion seen in these animals was mild interstitial nephritis in the pigs infected with PPV alone. These results indicate that lesions of PMWS can be induced by inoculating pigs with PCV2 alone, thereby fulfilling Koch's postulates. Concurrent infection with PPV increased the severity of the lesions, suggesting that co-factors are important in the pathogenesis of PMWS.     

Experimental infection of colostrum deprived piglets with porcine circovirus 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) potentiates PCV2 replication

Summary.  Experimental infection of colostrum-deprived (CD) pigs with a combined inoculum of porcine circovirus 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) potentiated the replication and distribution of PCV2 virus, when compared with pigs inoculated with PCV2 alone. The replication and distribution of PRRSV in dually infected pigs was not enhanced, when compared to pigs inoculated with PRRSV alone. The mechanisms involved in the potentiation of PCV2 replication in PCV2/PRRSV and PCV2/porcine parvovirus (PPV) dually infected pigs may relate to the fact that monocyte/macrophage cell types are common targets of these 3 viruses. Received May 2, 2000/Accepted May 24, 2000     

Influence of maternal antibodies on efficacy of porcine circovirus type 2 (PCV2) vaccination to protect pigs from experimental infection with PCV2

Due to the ubiquitous nature of porcine circovirus type 2 (PCV2) in the pig population and the increasing use of PCV2 vaccines in breeding herds, the majority of dams have been exposed to field PCV2 or PCV2 vaccines, resulting in piglets with varied levels of passively acquired PCV2 maternal antibodies. The objective of the current research was to investigate the influence of passively acquired anti-PCV2 antibodies on PCV2 vaccine efficacy. Sixty 26-day-old pigs were divided into four groups: vaccinated pigs with no maternal PCV2 antibodies at the time of vaccination (VAC-NEG; n = 9), vaccinated pigs with maternal PCV2 antibodies at the time of vaccination (VAC-POS; n = 21), nonvaccinated pigs with no maternal antibodies at the time of challenge (NVAC-CNEG; n = 15), and nonvaccinated pigs with maternal antibodies at the time of challenge (NVAC-CPOS; n = 15). Vaccinations and challenges were performed on trial days 0 and 28, respectively, according to group designation. The pigs were monitored for clinical signs of disease daily and weighed weekly, and blood was collected weekly. All pigs were necropsied on trial day 49, and tissues were evaluated for macroscopic and microscopic lesions. Serum was evaluated using PCV2 immunoglobulin G (IgG) and PCV2 IgM enzyme-linked immunosorbent assays, quantitative PCV2 PCR, and a serum PCV2 neutralizing antibody test. In comparison to NVAC-CPOS pigs, VAC-POS animals had significantly (P < 0.01) less severe microscopic PCV2-associated lymphoid lesions and significantly (P < 0.04) reduced PCV2 genomic copies in serum following PCV2 challenge. These results indicate that vaccination with Suvaxyn PCV2 One Dose reduces viremia and prevents microscopic lesions associated with PCV2 in the presence of maternal antibodies.     

Modified Indirect Porcine Circovirus (PCV) Type 2-Based and Recombinant Capsid Protein (ORF2)-Based Enzyme-Linked Immunosorbent Assays for Detection of Antibodies to PCV

Postweaning multisystemic wasting syndrome of swine associated with porcine circovirus (PCV) is a recently reported and economically important disease. Simple and reliable diagnostic methods are needed for detecting antibodies to PCV type 2 (PCV2) for monitoring of PCV infection. Here, we report the development of two modified indirect enzyme-linked immunosorbent assays (ELISAs): a PCV2 ELISA based on cell-culture-propagated PCV2 and an ORF2 ELISA based on recombinant major capsid protein. PCV2 and ORF2 ELISA detected antibodies to PCV2 and the capsid protein, respectively, in sera from pigs experimentally infected with PCV2 as early as 14 and 21 days postinoculation (dpi). The kinetics of the antibody response to PCV2 and the major capsid protein were similar. Repeatability tests revealed that the coefficients of variation of positive sera within and between runs for both assays were less than 30%. To validate the assays, PCV2 and ORF2 ELISAs were performed with 783 serum samples of young and adult pigs collected from different herds in the Midwestern United States and compared with an indirect immunofluorescent assay (IIF). Six out of 60 samples collected from nursery and growing pigs in 1987 were positive by both ELISA and IIF. Compared with IIF, the diagnostic sensitivity, specificity, and accuracy of PCV2 and ORF2 ELISAs were similar (>90%). The tests showed no cross-reactivity with antibodies to porcine parvovirus and porcine reproductive and respiratory syndrome virus. There was good agreement between the two ELISAs and between the ELISAs and IIF. The availability of the two ELISAs should accelerate our understanding of the host immune response to PCV2 and facilitate the development of prevention and control strategies by elucidating the ecology of PCV2 within swine populations.     

Modified indirect porcine circovirus (PCV) type 2-based and recombinant capsid protein (ORF2)-based enzyme-linked immunosorbent assays for detection of antibodies to PCV.

Postweaning multisystemic wasting syndrome of swine associated with porcine circovirus (PCV) is a recently reported and economically important disease. Simple and reliable diagnostic methods are needed for detecting antibodies to PCV type 2 (PCV2) for monitoring of PCV infection. Here, we report the development of two modified indirect enzyme-linked immunosorbent assays (ELISAs): a PCV2 ELISA based on cell-culture-propagated PCV2 and an ORF2 ELISA based on recombinant major capsid protein. PCV2 and ORF2 ELISA detected antibodies to PCV2 and the capsid protein, respectively, in sera from pigs experimentally infected with PCV2 as early as 14 and 21 days postinoculation (dpi). The kinetics of the antibody response to PCV2 and the major capsid protein were similar. Repeatability tests revealed that the coefficients of variation of positive sera within and between runs for both assays were less than 30%. To validate the assays, PCV2 and ORF2 ELISAs were performed with 783 serum samples of young and adult pigs collected from different herds in the Midwestern United States and compared with an indirect immunofluorescent assay (IIF). Six out of 60 samples collected from nursery and growing pigs in 1987 were positive by both ELISA and IIF. Compared with IIF, the diagnostic sensitivity, specificity, and accuracy of PCV2 and ORF2 ELISAs were similar (>90%). The tests showed no cross-reactivity with antibodies to porcine parvovirus and porcine reproductive and respiratory syndrome virus. There was good agreement between the two ELISAs and between the ELISAs and IIF. The availability of the two ELISAs should accelerate our understanding of the host immune response to PCV2 and facilitate the development of prevention and control strategies by elucidating the ecology of PCV2 within swine populations.     

Spread like a wildfire--the omnipresence of porcine circovirus type 2 (PCV2) and its ever-expanding association with diseases in pigs

The discovery of porcine circovirus type 2 (PCV2) in 1998 initiated intensive research on arguably the most economically important pathogen facing the global swine industry today. PCV2 infection is now widespread worldwide, and increasing numbers of disease conditions have been linked to PCV2 infection in pigs. In this special issue of Virus Research, leading experts in the field review the history, epidemiology, transmission, clinical and pathological features, immunology, pathogenesis, molecular biology and vaccine development of PCV2 and porcine circovirus associated disease (PCVAD). In addition, circovirus-like DNA sequences recently identified from humans and other animal species and their biological significances are also reviewed. The articles in this special issue identify gaps in current PCV2 research and offer insights for the direction of future research.     

Effects of porcine circovirus type 2 (PCV2) maternal antibodies on experimental infection of piglets with PCV2

To determine the effects of porcine circovirus type 2 (PCV2) maternal antibodies on and response to experimental PCV2 infection, 24 piglets were divided into four groups on the basis of the enzyme-linked immunosorbent assay titers of PCV2 maternal antibodies: group A (n = 6; sample/positive [S/P] ratio, <0.2), group B (n = 5; S/P ratio, >0.2 to <0.5), and groups C (n = 8) and D (n = 5) (S/P ratio, >0.5). Piglets in groups A, B, and C were inoculated with PCV2 at day 0 and challenged with PCV2 at day 42. Group D piglets were not exposed to PCV2 at day 0 but were challenged at day 42. Before challenge, seroconversion to PCV2 antibodies occurred in five of six group A piglets, and the antibody level rose above the cutoff level in one of five group B piglets. Viremia was detected in five of six, four of five, and two of eight pigs in groups A, B, and C, respectively. After challenge, PCV2 DNA was detectable from 7 to 21 days postchallenge in the sera from six of six, four of five, three of eight, and five of five pigs in groups A, B, C, and D, respectively. The results indicated that protection against PCV2 infection conferred by maternal antibodies is titer dependent: higher titers are generally protective, but low titers are not.     

Genetic variation of porcine circovirus type 2 (PCV2) and its relevance to vaccination, pathogenesis and diagnosis

Porcine circovirus-associated disease (PCVAD) encompasses a group of complex, multi-factorial syndromes, which are dependent on infection with porcine circovirus type 2 (PCV2). Current strains of PCV2 circulating in the field are classified into two groups, termed PCV2a and PCV2b. Outbreaks of severe PCVAD in North America and other countries are often linked to a shift from PCV2a to PCV2b as the predominant genotype. Therefore, genotype-specific differences in pathogenesis and antigenicity have been suggested. Overall, evidence suggests that virulence is a function of the specific PCV2 isolate, regardless of genotype. In addition, only minor antigenic differences have been reported. In terms of immunopathogenesis, a conserved decoy epitope, located in the C-terminal region of the capsid protein, provides an explanation for the inability to identify pathogenic differences between genotypes. Finally, genetic variation in PCV2 and the resulting consequences with respect to vaccination and diagnostics are discussed.     

Relationship between Ileal symbiont intracellularis and porcine proliferative enteritis.

The relationship between Ileal symbiont (IS) intracellularis, formerly known as a Campylobacter-like organism, and porcine proliferative enteritis (PE) was studied by use of pigs with experimentally transmitted PE. Twenty one pigs were experimentally inoculated with homogenized ileal mucosa from a pig that died with PE, and 7 were maintained as uninoculated controls. Fecal samples were collected, and pigs were necropsied weekly postinoculation. Light microscopy and electron microscopy were used to examine tissues for lesions of PE and infectious agents. DNA was extracted from the fecal samples and assayed for the presence of sequences specific for IS intracellularis by dot blot hybridization and polymerase chain reaction amplification. IS intracellularis was detected by the polymerase chain reaction in the feces of 20 of 21 inoculated pigs but not in the feces of uninoculated pigs. Seven inoculated pigs but no uninoculated pigs were detected shedding IS intracellularis by dot blot hybridization. Shedding was detected 1 to 5 weeks after inoculation, and clinical signs were seen in the second to fifth weeks after inoculation. Few pigs without lesions of PE were found to shed IS intracellularis. There was a highly significant association between the presence of IS intracellularis in feces or tissue and the presence of microscopic proliferative lesions and between the severity of the lesions of PE and the percentage of IS intracellularis-infected intestinal crypts. Pigs that ceased shedding IS intracellularis were significantly less likely to have proliferative lesions. These and previous reports are consistent with the hypothesis that IS intracellularis is a necessary causative agent of PE.     

PCR detection and evidence of shedding of porcine circovirus type 2 in boar semen

An experimental study was conducted to evaluate the potential presence of porcine circovirus type 2 (PCV2) in the semen of infected boars. Four mature boars were inoculated intranasally with PCV2 isolate LHVA-V53 propagated on PK15 cells. Two boars inoculated with the supernatant of noninfected PK15 cells were kept as controls. Serum samples were collected from all boars at 4, 7, 11, 13, 18, 21, 25, 28, 35, and 55 days postinoculation (dpi) and from the four PCV2-infected boars at 90 dpi. Samples were tested for the presence of antibodies to PCV2 by an indirect immunofluorescence assay and for the presence of PCV2 DNA by PCR and nested PCR. Semen samples were collected from all six boars at 5, 8, 11, 13, 18, 21, 25, 28, 33, and 47 dpi and tested for the presence of PCV2 DNA by a nested PCR assay. Antibodies to PCV2 could be detected as early as 11 dpi in one boar, and all four infected boars were found positive for PCV2 antibodies by 18 dpi. Thereafter all infected boars remained positive for antibodies to PCV2 until 90 dpi. Analysis of serum samples by nested PCR demonstrated the presence of PCV2 DNA as early as 4 dpi in three of four infected boars. Serum samples from all infected boars were positive for PCV2 DNA from 11 dpi until 35 dpi but were negative at 90 dpi. PCV2 DNA was detected as soon as 5 dpi in the semen of two infected boars and intermittently thereafter in the semen of all four infected boars. The semen of two infected boars was positive for PCV2 DNA at 47 dpi. Following infection, PCV2 DNA can be detected in semen concurrently with the presence of PCV2 DNA and antibodies in the serum. The present study suggests that PCV2 may be shed intermittently in the semen of infected boars.     

Simultaneous porcine circovirus type 2 and Mycoplasma hyopneumoniae co-inoculation does not potentiate disease in conventional pigs

The aim of this study was to assess the effect of simultaneous experimental inoculation of porcine circovirus type 2 (PCV2; intranasal delivery) and Mycoplasma hyopneumoniae (Mhyo; transtracheal delivery) into conventional, seropositive 6-week-old piglets. Thirty-six male piglets were assigned randomly to four groups: control (n=6), PCV2 (n=6), Mhyo (n=12) and PCV2+Mhyo (n=12). Blood samples and faecal and nasal swabs were collected at 0, 7, 14 and 21 days post inoculation (dpi). No significant clinical signs attributable to PCV2 infection were observed during the experiment. Coughing was recorded in three pigs from the Mhyo group and six from the PCV2+Mhyo group. No significant differences in mean body weight and rectal temperature were observed between the groups. Mild microscopical lesions similar to those reported for post-weaning multisystemic wasting syndrome were observed in two PCV2 pigs and in one PCV2+Mhyo animal. Mhyo-compatible lung lesions were observed in 21/24 pigs inoculated with Mhyo (10 from the Mhyo group and 11 from the PCV2+Mhyo group). PCV2 was detected by in-situ hybridization in 3/12 PCV2 and in 4/12 PCV2+Mhyo animals. No significant differences in PCV2 load (serum and nasal and faecal swabs), duration of viraemia or antibody titre were detected between PCV2-inoculated groups. No significant differences in Mhyo load in nasal swabs, percentage of Mhyo-seropositive pigs and mean lung score was detected between Mhyo-inoculated groups. Under the conditions of the present study, concurrent inoculation of PCV2 and Mhyo did not result in potentiation of clinical signs and lesions attributed to either infection.     

Cardiovascular lesions in pigs naturally or experimentally infected with porcine circovirus type 2

Abundant intracytoplasmic porcine circovirus type 2 (PCV2) was associated with myocardiocyte swelling or necrosis, or myocardial fibrosis (or both) in three naturally infected pigs aged 4-7 weeks from three different farms. One 6 week old pig from a fourth farm had severe diffuse segmental to circumferential lymphohistiocytic and plasmacytic periarteritis and endarteritis in several organs, PCV2 antigen was demonstrated in endothelial cells, and inflammatory cells in the arterial walls. In three pigs experimentally infected with PCV2, viral antigen was also associated with obliterated blood vessels in areas of granulomatous and necrotizing lymphadenitis. Together these findings suggest that the cardiovascular system in general and endothelial cells in particular play an important role in the pathogenesis of PCV2-associated diseases.     

Concurrent porcine circovirus type 2a (PCV2a) or PCV2b infection increases the rate of amino acid mutations of porcine reproductive and respiratory syndrome virus (PRRSV) during serial passages in pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) has a high degree of genetic and antigenic variability. The purpose of this study was to determine if porcine circovirus type 2 (PCV2) infection increases genetic variability of PRRSV during serial passages in pigs and to determine if there is a difference in the PRRSV mutation rate between pigs concurrently infected with PCV2a or PCV2b. After 8 consecutive passages of PRRSV alone (group 1), PRRSV with PCV2a (group 2), or PCV2b (group 3) in pigs, the sequences of PRRSV structural genes for open reading frame (ORF) 5, ORF6, ORF7 and the partial non-structural protein gene (Nsp) 2 were determined. The total number of identified amino acid mutations in ORF5, ORF6, ORF7 and Nsp2 sequences was 30 for PRRSV infection only, 63 for PRRSV/PCV2a concurrent infection, and 77 for PRRSV/PCV2b concurrent infection when compared with the original VR2385 virus used to infect the passage 1 pigs. Compared to what occurred in pigs infected with PRRSV only, the mutation rates in ORF5 and ORF6 were significantly higher for concurrent PRRSV/PCV2b infected pigs. The PRRSV/PCV2a pigs had a significantly higher mutation rate in ORF7. The results from this study indicated that, besides ORF5 and Nsp2, the PRRSV structural genes ORF6 and ORF7 were shown to mutate at various degrees when the PRRSV was passaged over time in vivo. Furthermore, a significantly higher mutation rate of PRRSV was observed when pigs were co-infected with PCV2 highlighting the importance of concurrent infections on PRRSV evolution and control.