Clinical and pathological observations on pigs with postweaning multisystemic wasting syndrome

Isolation of porcine circovirus 3 using primary porcine bone marrow-derived cells

Porcine circovirus 3 (PCV3) was first reported in the United States in 2016; this virus is considered to be involved in diverse pathologies, such as multisystem inflammation, porcine dermatitis and nephropathy syndrome, and reproductive disorders. However, successful isolation of PCV3 using cultured cells has been rare. In this study, we aimed to isolate PCV3 using primary porcine bone marrow-derived cells. Mononuclear cells were isolated from the femur bones of clinically healthy pigs. These primary cells were cultured for 6-10 days post-seeding and infected with PCV3-containing tissue homogenates. The cells were cultured for up to 37 days, and the culture medium was changed every 3-4 days. The growth curve of PCV3 in porcine bone marrow cells revealed a decline in growth during the first 10 days post-infection, followed by an increase leading to > 1010 genomic copies/mL of the cell culture supernatant; moreover, the virus was capable of passaging. The indirect fluorescent antibody assay for PCV3 infection revealed the presence of PCV3 capsid protein in the cytoplasm and nuclei of infected cells. Bone marrow cells were passaged for more than 20 generations (over 5 months), and PCV3 persistently infected the cells. PCV3-infected bone marrow cells expressed mesenchymal markers. These results reflect that primary porcine bone marrow-derived mesenchymal cells are permissive to PCV3 and continuously replicate a high copy number of the PCV3 genome. These findings regarding the high replication rate of PCV3 in bone marrow-derived mesenchymal cells could enhance our understanding of PCV3 pathogenicity.

Interaction between host cell proteins and open reading frames of porcine circovirus type 2

Postweaning multisystemic wasting syndrome (PMWS) is caused by a systemic inflammation after porcine circovirus type 2 (PCV2) infection. It was one of the most economically important pathogens affecting pig production worldwide before PCV2 vaccine was first introduced in 2006. After the development of a vaccine against PCV2a type, pig farms gradually restored enormous economic losses from PMWS. However, vaccine against PCV2a type could not be fully effective against several different PCV2 genotypes (PCV2b - PCV2h). In addition, PCV2a vaccine itself could generate antigenic drift of PCV2 capsid. Therefore, PCV2 infection still threats pig industry worldwide. PCV2 infection was initially found in local tissues including reproductive, respiratory, and digestive tracks. However, PCV2 infection often leads to a systemic inflammation which can cause severe immunosuppression by depleting peripheral lymphocytes in secondary lymphoid tissues. Subsequently, a secondary infection with other microorganisms can cause PMWS. Eleven putative open reading frames (ORFs) have been predicted to encode PCV2 genome. Among them, gene products of six ORFs from ORF1 to ORF6 have been identified and characterized to estimate its functional role during PCV2 infection. Acquiring knowledge about the specific interaction between each PCV2 ORF protein and host protein might be a key to develop preventive or therapeutic tools to control PCV2 infection. In this article, we reviewed current understanding of how each ORF of PCV2 manipulates host cell signaling related to immune suppression caused by PCV2.

Assessment on the efficacy of methods 2 to 5 and method 7 set out in Commission Regulation (EU) No 142/2011 to inactivate relevant pathogens when producing processed animal protein of porcine origin intended to feed poultry and aquaculture animals

An assessment was conducted on the level of inactivation of relevant pathogens that could be present in processed animal protein of porcine origin intended to feed poultry and aquaculture animals when methods 2 to 5 and method 7, as detailed in Regulation (EU) No 142/2011, are applied. Five approved scenarios were selected for method 7. Salmonella Senftenberg, Enterococcus faecalis, spores of Clostridium perfringens and parvoviruses were shortlisted as target indicators. Inactivation parameters for these indicators were extracted from extensive literature search and a recent EFSA scientific opinion. An adapted Bigelow model was fitted to retrieved data to estimate the probability that methods 2 to 5, in coincidental and consecutive modes, and the five scenarios of method 7 are able to achieve a 5 log10 and a 3 log10 reduction of bacterial indicators and parvoviruses, respectively. Spores of C. perfringens were the indicator with the lowest probability of achieving the target reduction by methods 2 to 5, in coincidental and consecutive mode, and by the five considered scenarios of method 7. An expert knowledge elicitation was conducted to estimate the certainty of achieving a 5 log10 reduction of spores of C. perfringens considering the results of the model and additional evidence. A 5 log10 reduction of C. perfringens spores was judged: 99-100% certain for methods 2 and 3 in coincidental mode; 98-100% certain for method 7 scenario 3; 80-99% certain for method 5 in coincidental mode; 66-100% certain for method 4 in coincidental mode and for method 7 scenarios 4 and 5; 25-75% certain for method 7 scenario 2; and 0-5% certain for method 7 scenario 1. Higher certainty is expected for methods 2 to 5 in consecutive mode compared to coincidental mode.

Detection of porcine circovirus type 2 (PCV2) in the Philippines and the complexity of PCV2-associated disease diagnosis

Porcine circovirus type 2 (PCV2), an important pig viral pathogen, can cause porcine circovirus-associated disease (PCVAD), resulting in economic losses associated with decreased growth and mortalities. The diagnosis of PCVAD is complex requiring clinical, pathological and virological approaches. This study assessed PCV2 infection using histopathology and immunohistochemistry (IHC) on tissue samples and quantitative polymerase chain reaction (qPCR) on serum samples from 47 grower-finisher pigs allocated in three clinical groups in the Philippines. Typical PCV2 histopathological lesions were observed in mediastinal lymph nodes (MLN) of eight of 47 pigs. Lymphoid depletion was seen in all eight pigs and granulomatous inflammation in one of these pigs. Four of these eight pigs were PCV2 positive by both IHC and qPCR. IHC revealed PCV2 antigen in 8 pigs in at least one of the following tissues: MLN (5/8), spleen (3/8), tonsils (4/8) and lungs (5/8). PCV2 antigen was observed in 3/8 MLN with lymphoid depletion and in one MLN with depletion and granulomatous inflammation. The qPCR test showed that 33 sera had a non-detectable level, twelve had < 10⁶ and two had > 10⁶ PCV2 DNA copies/ml serum. One pig with lymphoid depletion had > 10⁶ PCV2 DNA copies/ml serum, and another pig without MLN lesions also had > 10⁶ PCV2 DNA copies/ml serum. These findings suggest that PCVAD is present in the Philippines and confirm the challenges of PCVAD diagnosis as different patterns of results were obtained from the different tests.

Risk factors for gastric ulceration in nursery pigs

Pars oesophageal gastric ulceration is a prevalent condition in swine production and often observed in finisher pigs at slaughter, with reported prevalence ranging from 32 % to 65 %. Although feeding practices in nursery and finisher pigs are similar, little is known about the prevalence and risk factors associated with this condition in nursery pigs. This prospective cohort study aimed to identify risk factors for gastric ulceration in nursery pigs. The objectives were: (1) to estimate the association of inherent pig characteristics (birth weight, sex, parity of sow, litter size, and pen fouling behavior) and management characteristics (antibiotic treatment during suckling and post weaning, piglet rotation during lactation, weaning age and weight) with pars oesophageal lesions; (2) to assess differences in gastric dry matter content, pH, and percentage of solid particles in the sediment in relation to pars oesophageal lesions. A total of 58 piglets tracked from birth to 20 days of age and 210 nursery pigs from birth to 10 weeks of age were euthanized and assessed for pars oesophageal gastric lesions. All nursery pigs were fed finely ground pelleted feed ad libitum. Based on a macroscopic assessment, the pigs' stomachs were categorized as either LPO "lesions in the Pars oesophagea" or NLPO "no lesions in the Pars oesophagea". We observed an overall prevalence of 26.2 % (CI 95 % 0.67 - 0.79) for LPO in nursery pigs at 10 weeks of age, while no lesion were observed in piglets at 20 days of age. A mixed multivariable logistic regression model showed that piglets with a birthweight ≤ 1.11 kg had a 2.11 times higher odds of LPO (CI 95 % 1.02-4.37, p = 0.04) than their heavier counterparts. There was a weak association of LPO in nursery pigs from pens with pen fouling with a 2.14 times higher odds (CI 95 % 0.97-4.72 p = 0.05). Nursery pigs with LPO presented an increased gastric content fluidity with a reduced (p ≤ 0.01) gastric dry matter content (18.7 %), solid phase (74.7 %), and pH (3.22) compared to NLPO nursery pigs (20.5 %, 85.09 %, 3.56, respectively). We have demonstrated that LPO are present in nursery pigs as early as 10 weeks of age. We observed that low birth weight is associated with higher odds for LPO in nursery pigs. These observations might help explain differences between individual pigs in terms of LPO development when groups are exposed to similar environments, management, and feeding conditions.

Safety and long-lasting immunity of the combined administration of a modified-live virus vaccine against porcine reproductive and respiratory syndrome virus 1 and an inactivated vaccine against porcine parvovirus and Erysipelothrix rhusiopathiae in breeding pigs

BACKGROUND

In the field, vaccination schedules based on modified-live virus (MLV) vaccines administered twice in gilts and every three to four months in sows are commonly used to immunize breeding herds against porcine reproductive and respiratory virus (PRRSV). Breeding sows are repeatedly vaccinated against several other agents. Thus, the combined administration of vaccines for their simultaneous use can simplify such complex immunization schedules. Here, we evaluated the safety and long-term immunity of the authorized combined administration of a PRRSV MLV vaccine and an inactivated vaccine against porcine parvovirus (PPV) and Erysipelothrix rhusiopathiae for their simultaneous use.Six-month-old naïve healthy gilts were vaccinated at day 0 and revaccinated at days 21 and 147, mimicking the abovementioned vaccination schedule. Systemic and local reactions, as well as body temperature, were measured. The excretion of PRRSV1 MLV was evaluated in oral fluids. Humoral responses against the three antigens were measured by ELISA. For PRRSV, homologous neutralizing antibodies (NAs) and homologous and heterologous cell-mediated immunity (CMI) were also assessed.

RESULTS

The combined administration of the tested vaccines, applied according to the manufacturer's instructions, was safe based on all evaluated parameters. Overall, we detected antibodies against PPV and PRRSV in all vaccinated pigs already after the first vaccination, whereas antibodies against E. rhusiopathiae were observed in all animals after revaccination. After subsequent revaccinations, we observed boosts for the humoral response for PPV at days 28 and 154 and at day 154 for E. rhusiopathiae. No boosts were detected during the experiment by PRRSV ELISA. In all vaccinated animals, homologous NAs against MLV were already detected before revaccination (day 21). After revaccination, there was a boost with mean titres of homologous NAs remaining constant thereafter. Concerning CMI, PRRSV-specific IFN-γ-secreting cells were already detected at day 21 for all evaluated strains and we observed boosts for all PRRSV1 strains after revaccination and recall revaccination.

CONCLUSIONS

We showed that the combined administration of tested vaccines described here using a vaccination schedule against PRRSV commonly implemented for breeding pigs in the field is safe and induces long-lasting humoral and cellular immunity against PRRSV, PPV, and E. rhusiopathiae.

Porcine circovirus 2 in the North Eastern region of India: Disease prevalence and genetic variation among the isolates from areas of intensive pig rearing

Porcine Circovirus type-2 (PCV-2) is considered as a major threat to the piggery sector in India. To ascertain the epidemiological status and infection level of PCV2, a pilot study was undertaken to find out the prevalence of PCV2 in swine population by ELISA and PCR in the interior and border areas of Meghalaya which includes the area where accessibility and medical aid is a rare phenomenon. A total of 249 serum samples were collected from October 2014 to February 2016 from three divisions of Meghalaya: Khasi, Jaintia and Garo Hills Divisions. The mean positivity of PCV-2 antibodies in suspected sera was 83.93% whereas 62.25% of the suspected samples respectively were found to contain PCV2 as detected by PCR. Additional 190 tissue samples were collected during necropsy from both symptomatic and asymptomatic animals following reported outbreak in this region, which indicated a mean positivity of 18.94% (36/190); out of which 13 samples were subjected to sequencing to find out the genetic diversity of PCV2 amongst the field isolates. Molecular characterization and phylogenetic analysis of PCV2 isolates based on cap gene depicted genetic diversity among the strains in pig population of Meghalaya as the isolates belonged to PCV2a, PCV2b-1c and PCV2d genotypes; identification of the PCV2d genotype is probably the first report from Meghalaya. Four isolates forming an outlier group in the phylogenetic tree were arising out of natural inter-genotypic recombination between PCV2a and PCV2b. PCV2 being immunosuppressive in nature impairs the host immune response increasing the susceptibility to other co-infections leading to disease severity and high mortality in pig population. This baseline data gives a brief epidemiological status of PCV2 infection and circulating PCV2 genotype in this region which will be useful in the formulation of control and eradication programs in remotes areas of Meghalaya where accessibility is less and vaccination is a rare practice.

Seroprevalence of selected viral pathogens in pigs reared in organized farms of Meghalaya from 2014 to 16

Aim:

A pilot study was carried out to find out the seroprevalence of Porcine circovirus 2 (PCV2), classical swine fever virus (CSFV), and Porcine respiratory and reproductive syndrome virus (PRRS) in pig population of Meghalaya.

Materials and Methods:

Serum samples were collected from piglets of 40–45 days age group, growers, and sows reared under organized and unorganized management in 11 districts of Meghalaya situated in the Khasi, Jaintia, and Garo hills divisions in the time period of 2014-2016 from apparently healthy and suspected pigs. Seroprevalence of PCV2, CSFV, and PRRS specific antibodies was detected by enzyme-linked immunosorbent assay (ELISA).

Results:

A total of 1899 serum samples were collected and screened using antibody ELISA kits specific for PCV2, CSFV, and PRRS. The highest antibody prevalence during the selected time periods was detected for PCV2 (80.8% in 2014, 79.1% in 2015, and 96.2% in 2016) followed by CSFV (76.4% in 2014, 66.09% in 2015, and 25.5% in 2016) and PRRS (2.8% in 2014, 2.7% in 2015, and 3.62% in 2016). The result indicates high seroprevalence for PCV2, which can be considered as an inducement factor due to the immunosuppressive nature of the virus, for animals being susceptible to other pathogens in farms where airborne transmission of PCV2 and postweaning multisystemic wasting syndrome among animals reared in close pens can be a major possibility.

Conclusions:

The data from this study indicates ubiquitous prevalence of PCV2 antibodies in the farm animals along with the endemic presence of swine fever and emergence of PRRS in an organized farm. There are few reports regarding PCV2 infections/outbreaks in pigs associated with reproductive failure from northern and southern part of India, but till date, there are no reports regarding concomitant infection of CSFV and PCV2 from India. Considerable high seropositivity of PCV2 indicates the need for high impact hygiene practice in farms, routine seromonitoring and implementation the vaccination program. To the author’s best knowledge, this is the first documented report on the seroprevalence of PCV2, CSFV, and PRRS from pig population of Meghalaya.

Transmission of Porcine reproductive and respiratory syndrome virus 1 to and from vaccinated pigs in a one-to-one model

The present study examined transmission by contact of Porcine reproductive and respiratory syndrome virus (PRRSV) 1 in a one-to-one model to vaccinated and unvaccinated pigs and from vaccinated infected pigs to other vaccinated pigs. The experiment started by randomly assigning weaned pigs to groups V (n=24) and U (n=26). V pigs were vaccinated with a commercial live attenuated PRRSV vaccine and the U animals were kept as unvaccinated controls. Twenty-eight days later, 6U pigs were separated and allocated in individual boxes. The remaining 20U pigs were intranasally inoculated with PRRSV isolate 3267 (from now on designated as seeder (S) pigs) and 48h later were distributed in boxes where they were commingled with either V or U pigs in 1:1 groups (first contact phase), resulting in 6S:U and 14S:V pairs. As soon as a V pig was detected to be viremic because of contact with a S, the infected V (from now on designated as V_inf) was transferred (<24h after detection) to a new pen where it was comingled with a new V pig (designated as V₂) in a second contact phase. For the first contact phase, pigs were maintained 21days at maximum and for the second contact phase the maximum exposure period was 14days. Two V pigs tested positive for the vaccine virus (>99.5% similarity) when they were relocated with the corresponding V₂ pigs and they were removed; thus, only 12V_inf were finally considered. All V pigs (12/12) exposed to S animals became infected although the first detection of viremia occurred at 13.6±3.6days, one week later than in U (p<0.05). Also, duration of viremia was shorter for V_inf compared to U, (5.5±4.3days versus 12.5±2.7days). The V_inf group showed remarkable individual variability: eight animals had a viremic period of 5 or less days (3.0±1.4) while the remaining four had a longer viremic period of more than one week (10.8±2.9). This situation was not observed in U. In the second contact phase, transmission from V_inf to V₂ pigs occurred in 7/8 cases (87.5%). The mean duration of viremia for V₂ was 4.8±3.4 and two different patterns were again observed: two animals had viremias of 9-10days and the rest averaged 3.0±1.4days (range: 2-5days). Vaccinated groups V_inf and V₂ had a significantly lower PRRSV shedding in oral fluids for at least the first 9days after the onset of the viremia compared to U, and shedding for V2 was even significantly lower (p<0.05) than shedding for V_inf. Our experimental design reproduced the worst-case scenario for evaluating the effect of vaccination and, under such conditions; it was still efficacious in slowering PRRSV transmission and decreasing the global viral load and particularly oral shedding.

Retrospective Analysis of Bacterial and Viral Co-Infections in Pneumocystis spp. Positive Lung Samples of Austrian Pigs with Pneumonia

Aim of this study was the retrospective investigation of viral (porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV), torque teno sus virus type 1 and 2 (TTSuV1, TTSuV2)) and bacterial (Bordetella bronchiseptica (B. b.), Mycoplasma hyopneumoniae (M. h.), and Pasteurella multocida (P. m.)) co-infections in 110 Pneumocystis spp. positive lung samples of Austrian pigs with pneumonia. Fifty-one % were positive for PCV2, 7% for PRRSV, 22% for TTSuV1, 48% for TTSuV2, 6% for B. b., 29% for M. h., and 21% for P. m. In 38.2% only viral, in 3.6% only bacterial and in 40.0% both, viral and bacterial pathogens were detected. In 29.1% of the cases a co-infection with 1 pathogen, in 28.2% with 2, in 17.3% with 3, and in 7.3% with 4 different infectious agents were observed. The exposure to Pneumocystis significantly decreased the risk of a co-infection with PRRSV in weaning piglets; all other odds ratios were not significant. Four categories of results were compared: I = P. spp. + only viral co-infectants, II = P. spp. + both viral and bacterial co-infectants, III = P. spp. + only bacterial co-infectants, and IV = P. spp. single infection. The evaluation of all samples and the age class of the weaning piglets resulted in a predomination of the categories I and II. In contrast, the suckling piglets showed more samples of category I and IV. In the group of fattening pigs, category II predominated. Suckling piglets can be infected with P. spp. early in life. With increasing age this single infections can be complicated by co-infections with other respiratory diseases.

Experimental Reproduction of Postweaning Multisystemic Wasting Syndrome in Pigs by Dual Infection with Mycoplasma hyopneumoniae and Porcine Circovirus Type 2

The objectives of this study were to investigate the interactions between Mycoplasma hyopneumoniae and porcine circovirus type 2 (PCV2) and to establish a model for studying the pathogenesis of and testing intervention strategies for the control of PCV2-associated porcine respiratory disease complex (PRDC). Sixty-seven pigs were randomly assigned to four groups. Group 1 ( n = 17) pigs served as controls, group 2 ( n = 17) pigs were inoculated with M. hyopneumoniae, group 3 ( n = 17) pigs were dual infected with M. hyopneumoniae and PCV2, and group 4 ( n = 16) pigs were inoculated with PCV2. Pigs were inoculated intratracheally with M. hyopneumoniae at 4 weeks of age followed by intranasal inoculation with PCV2 at 6 weeks of age. Dual-infected pigs had moderate dyspnea, lethargy, and reduced weight gain. The overall severity of macroscopic lung lesions, PCV2-associated microscopic lesions in lung and lymphoid tissues, and the amount of PCV2-antigen associated with these lesions were significantly ( P < 0.05) higher in dual-infected pigs compared with all other groups. Four of 17 (23.5%) dual-infected pigs had decreased growth rate and severe lymphoid depletion and granulomatous lymphadenitis associated with high amounts of PCV2-antigen consistent with postweaning multisystemic wasting syndrome (PMWS). PCV2-antigen in lung tissue was most often associated with M. hyopneumoniae-induced peribronchial lymphoid hyperplasia, suggesting that this is an important site for PCV2 replication in the lung. This study indicates that M. hyopneumoniae potentiates the severity of PCV2-associated lung and lymphoid lesions, increases the amount and prolongs the presence of PCV2-antigen, and increases the incidence of PMWS in pigs.

Microbiome associations in pigs with the best and worst clinical outcomes following co-infection with porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2)

On a world-wide basis, co-infections involving porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) are common and contribute to a range of polymicrobial disease syndromes in swine. Both viruses compromise host defenses, resulting in increased susceptibility to infections by primary and secondary pathogens that can affect growth performance as well as increased morbidity and mortality. An experimental population of 95 pigs was co-infected with PRRSV and PCV2. At 70days post-infection (dpi), 20 representative pigs were selected as having the best or worst clinical outcome based on average daily gain (ADG) and the presence of clinical disease. Worst clinical outcome pigs had prolonged and greater levels of viremia as measured by qPCR. Serum, lung and fecal samples collected at 70 dpi were analyzed using a comprehensive DNA microarray technology, the Lawrence Livermore Microbial Detection Array, to detect over 8000 microbes. Bacterial species, such as Bacillus cereus, were detected at a higher rate in the serum of worst performing pigs. At the level of the fecal microbiome, the overall microbial diversity was lower in the worst clinical outcome group. The results reinforce the importance of pathogen load in determining clinical outcome and suggest an important role of microbial diversity as a contributing factor in disease.

A review of fibropapillomatosis in Green turtles (Chelonia mydas)

Despite being identified in 1938, many aspects of the pathogenesis and epidemiology of fibropapillomatosis (FP) in marine turtles are yet to be fully uncovered. Current knowledge suggests that FP is an emerging infectious disease, with the prevalence varying both spatially and temporally, even between localities in close proximity to each other. A high prevalence of FP in marine turtles has been correlated with residency in areas of reduced water quality, indicating that there is an environmental influence on disease presentation. Chelonid herpesvirus 5 (ChHV5) has been identified as the likely aetiological agent of FP. The current taxonomic position of ChHV5 is in the family Herpesviridae, subfamily Alphaherpesvirinae, genus Scutavirus. Molecular differentiation of strains has revealed that a viral variant is typically present at specific locations, even within sympatric species of marine turtles, indicating that the disease FP originates regionally. There is uncertainty surrounding the exact path of transmission and the conditions that facilitate lesion development, although recent research has identified atypical genes within the genome of ChHV5 that may play a role in pathogenesis. This review discusses emerging areas where researchers might focus and theories behind the emergence of FP globally since the 1980s, which appear to be a multi-factorial interplay between the virus, the host and environmental factors influencing disease expression.

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.

Expression of antigenic epitopes of porcine reproductive and respiratory syndrome virus (PRRSV) in a modified live-attenuated porcine circovirus type 2 (PCV2) vaccine virus (PCV1-2a) as a potential bivalent vaccine against both PCV2 and PRRSV

Co-infection of pigs in the field with porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) is common and poses a major concern in effective control of PCV2 and PRRSV. We previously demonstrated that insertion of foreign epitope tags in the C-terminus of PCV2 ORF2 produced infectious virions that elicited humoral immune responses against both PCV2 capsid and inserted epitope tags. In this study, we aimed to determine whether the non-pathogenic chimeric virus PCV1-2a, which is the basis for the licensed PCV2 vaccine Fostera PCV, can express PRRSV antigenic epitopes, thus generating dual immunity as a potential bivalent vaccine against both PCV2 and PPRSV. Four different linear B-cell antigenic epitopes of PRRSV were inserted into the C-terminus of the capsid gene of the PCV1-2a vaccine virus. We showed that insertion of 12 (PRRSV-GP2 epitope II, PRRSV-GP3 epitope I, and PRRSV-GP5 epitope I), and 14 (PRRSV-GP5 epitope IV) amino acid residues did not impair the replication of the resulting PCV1-2a-PRRSVEPI chimeric viruses in vitro. The four chimeric PCV1-2a viruses expressing PRRSV B-cell linear epitopes were successfully rescued and characterized. An immunogenicity study in pigs revealed that two of the four chimeric viruses, PCV1-2a-PRRSVEPIGP3IG and PCV1-2a-PRRSVEPIEPIGP5IV, elicited neutralizing antibodies against PRRSV VR2385 as well as PCV2 (strains PCV2a, PCV2b, and mPCV2b). The results have important implications for exploring the potential use of PCV1-2a vaccine virus as a live virus vector to develop bivalent MLVs against both PCV2 and PRRSV.

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.

Vaccination with a genotype 1 modified live vaccine against porcine reproductive and respiratory syndrome virus significantly reduces viremia, viral shedding and transmission of the virus in a quasi-natural experimental model

The present study assessed the efficacy of vaccination against genotype 1 porcine reproductive and respiratory syndrome virus (PRRSV) in terms of reduction of the transmission. Ninety-eight 3-week-old piglets were divided in two groups: V (n=40) and NV (n=58) that were housed separately. V animals were vaccinated with a commercial genotype 1 PRRSV vaccine while NV were kept as controls. On day 35 post-vaccination, 14 NV pigs were separated and inoculated intranasally with 2 ml of a heterologous genotype 1 PRRSV isolate ("seeder" pigs, SP). The other V and NV animals were distributed in groups of 5 pigs each. Two days later, one SP was introduced into each pen to expose V and NV to PRRSV. Sentinel pigs were allocated in adjacent pens. Follow-up was of 21 days. All NV (30/30) became viremic after contact with SP while only 53% of V pigs were detected so (21/40, p<0.05). Vaccination shortened viremia (12.2±4 versus 3.7±3.4 days in NV and V pigs, respectively, p<0.01). The 50% survival time for becoming infected (Kaplan-Meier) for V was 21 days (CI95%=14.1-27.9) compared to 7 days (CI95%=5.2-8.7) for NV animals (p<0.01). These differences were reflected in the R value as well: 2.78 (CI95%=2.13-3.43) for NV and 0.53 (CI95%=0.19-0.76) for V pigs (p<0.05). All sentinel pigs (10/10) in pens adjacent to NV+SP pens got infected compared to 1/4 sentinel pigs allocated contiguous to a V+SP pen. These data show that vaccination of piglets significantly decrease parameters related to PRRSV transmission.

CD44 deficiency leads to decreased proinflammatory cytokine production in lung induced by PCV2 in mice

Porcine circovirus type 2 (PCV2) is the primary etiological agent of postweaning multisystemic wasting syndrome (PMWS). CD44 is a widely expressed class I transmembrane glycoprotein implicated in immunological and inflammatory responses. In previous studies, the role of CD44 in host defense against microorganism infection remains controversial. The role of CD44 in host defense against PCV2 infection has never been studied before. In this study, we investigated the role of CD44 in the development of pneumonia induced by PCV2 in mice model. Upon infection, CD44 mRNA level in lung tissue was upregulated, and we confirmed a detrimental role of CD44 in host defense against PCV2 infection. The results demonstrated that CD44 deficiency could result in decreased proinflammatory cytokine production in lung induced by PCV2 in mice, suggesting a previously unrecognized role for CD44 in the development of pneumonia response to PCV2 infection.

Economic efficiency analysis of different strategies to control post-weaning multi-systemic wasting syndrome and porcine circovirus type 2 subclinical infection in 3-weekly batch system farms

The study assessed the economic efficiency of different strategies for the control of post-weaning multi-systemic wasting syndrome (PMWS) and porcine circovirus type 2 subclinical infection (PCV2SI), which have a major economic impact on the pig farming industry worldwide. The control strategies investigated consisted on the combination of up to 5 different control measures. The control measures considered were: (1) PCV2 vaccination of piglets (vac); (2) ensuring age adjusted diet for growers (diets); (3) reduction of stocking density (stock); (4) improvement of biosecurity measures (bios); and (5) total depopulation and repopulation of the farm for the elimination of other major pathogens (DPRP). A model was developed to simulate 5 years production of a pig farm with a 3-weekly batch system and with 100 sows. A PMWS/PCV2SI disease and economic model, based on PMWS severity scores, was linked to the production model in order to assess disease losses. This PMWS severity scores depends on the combination post-weaning mortality, PMWS morbidity in younger pigs and proportion of PCV2 infected pigs observed on farms. The economic analysis investigated eleven different farm scenarios, depending on the number of risk factors present before the intervention. For each strategy, an investment appraisal assessed the extra costs and benefits of reducing a given PMWS severity score to the average score of a slightly affected farm. The net present value obtained for each strategy was then multiplied by the corresponding probability of success to obtain an expected value. A stochastic simulation was performed to account for uncertainty and variability. For moderately affected farms PCV2 vaccination alone was the most cost-efficient strategy, but for highly affected farms it was either PCV2 vaccination alone or in combination with biosecurity measures, with the marginal profitability between 'vac' and 'vac+bios' being small. Other strategies such as 'diets', 'vac+diets' and 'bios+diets' were frequently identified as the second or third best strategy. The mean expected values of the best strategy for a moderately and a highly affected farm were £14,739 and £57,648 after 5 years, respectively. This is the first study to compare economic efficiency of control strategies for PMWS and PCV2SI. The results demonstrate the economic value of PCV2 vaccination, and highlight that on highly affected farms biosecurity measures are required to achieve optimal profitability. The model developed has potential as a farm-level decision support tool for the control of this economically important syndrome.

Current State of Knowledge on Porcine Circovirus Type 2-Associated Lesions

Porcine circovirus type 2 (PCV2), a small single-stranded DNA virus, was initially discovered in 1998 and is highly prevalent in the domestic pig population. Disease manifestations associated with PCV2 include postweaning multisystemic wasting disease (PMWS), enteric disease, respiratory disease, porcine dermatitis and nephropathy syndrome (PDNS), and reproductive failure. Although these clinical manifestations involve different organ systems, there is considerable overlap in clinical expression of disease and presence of lesions between pigs and within herds. It is now widely accepted that PCV2 can be further subdivided into different types, of which PCV2a and PCV2b are present worldwide and of greatest importance. This review will focus on PCV2-associated lesions in different organ systems.

Porcine circovirus type 2 infection before and during an outbreak of postweaning multisystemic wasting syndrome on a pig farm in the UK

The presence of porcine circovirus type 2 (PCV-2) and other pathogens before and during an outbreak of postweaning multisystemic wasting syndrome (PWMS) in pigs is evaluated in this study. At the time of the outbreak on a large commercial pig farm in the UK, serum samples and data were collected in two independent on-going research projects, one in weaned pigs and the other in sows. Serum samples of growing pigs and sows were PCV-2-antibody and PCR positive before and during the PMWS outbreak. Upon sequencing, PCV-2 isolates collected before the outbreak were identified as PCV-2a, and isolates collected during the outbreak were identified as PCV-2b, suggesting a shift of PCV-2 genotypes present on the farm. Pigs in the weaner study were from sows originating from different breeders and an association of sow origin and PCV-2 serostatus in offspring was found. Further, pigs had higher odds to be PCV-2 antigen positive if the sow was PCV-2 antibody positive around farrowing, the sow was of higher parity, and were less likely to test antigen positive if the sow was sourced from a particular breeder. The findings of this study highlight the potential role of the immune status of the sow on the occurrence of PMWS.

Microarray analysis of mediastinal lymph node of pigs naturally affected by postweaning multisystemic wasting syndrome

Postweaning multisystemic wasting syndrome (PMWS) is one of the pig diseases with major economic impact worldwide. Clinical, pathologic and some immunologic aspects of this disease are relatively well-known, but the molecular mechanisms underlying the pathogenic mechanisms of the disease are still poorly understood. The objective of the present study was to investigate the global transcriptome changes in the mediastinal lymph nodes from pigs naturally affected by PMWS, as well as healthy counterparts, using the Affymetrix Porcine Genechip(®). From 366 transcripts showing significant differential abundance in the PMWS group of pigs relative to healthy animals, 229 showed higher and 137 lower abundance. A relative increased abundance of mRNAs coded by a large set of genes involved in the inflammatory responses (e.g. cytokines, acute phase proteins, and respiratory burst) was observed in PMWS affected pigs. The Gpnmb and Lgals3 genes, which have antagonistic functions in regulation of inflammatory processes, showed high mRNA levels in diseased pigs. The complement system was altered by PMWS, notably by the lower levels of Cr1 mRNA, which might favour both complement deposition and secondary infections by impairing phagocytosis. Decreased mRNA abundance of several genes involved in lymphocyte activation/differentiation, such as Cd79b, Cd19, Cd21 and MybL1, and the high level of Vsig4 mRNA, which can compromise the activation of residing T-cells, pointed towards a defective adaptive immunity. This is the first study on gene expression in pigs naturally affected by PMWS. The present results allowed identifying potential mechanisms underlying the inflammation and lymphocyte depletion in lymphoid tissues by complement mediated damage and immunosuppression, which are key features of PMWS.

Suitability and limitations of portion-specific abattoir data as part of an early warning system for emerging diseases of swine in Ontario

BACKGROUND

Abattoir data have the potential to provide information for geospatial disease surveillance applications, but the quality of the data and utility for detecting disease outbreaks is not well understood. The objectives of this study were to 1) identify non-disease factors that may bias these data for disease surveillance and 2) determine if major disease events that took place during the study period would be captured using multi-level modelling and scan statistics. We analyzed data collected at all provincially-inspected abattoirs in Ontario, Canada during 2001-2007. During these years there were outbreaks of porcine circovirus-associated disease (PCVAD), porcine reproductive and respiratory syndrome (PRRS) and swine influenza that produced widespread disease within the province. Negative binomial models with random intercepts for abattoir, to account for repeated measurements within abattoirs, were created. The relationships between partial carcass condemnation rates for pneumonia and nephritis with year, season, agricultural region, stock price, and abattoir processing capacity were explored. The utility of the spatial scan statistic for detecting clusters of high partial carcass condemnation rates in space, time, and space-time was investigated.

RESULTS

Non-disease factors that were found to be associated with lung and kidney condemnation rates included abattoir processing capacity, agricultural region and season. Yearly trends in predicted condemnation rates varied by agricultural region, and temporal patterns were different for both types of condemnations. Some clusters of high condemnation rates of kidneys with nephritis in time and space-time preceded the timeframe during which case clusters were detected using traditional laboratory data. Yearly kidney condemnation rates related to nephritis lesions in eastern Ontario were most consistent with the trends that were expected in relation to the documented disease outbreaks. Yearly lung condemnation rates did not correspond with the timeframes during which major respiratory disease outbreaks took place.

CONCLUSIONS

This study demonstrated that a number of abattoir-related factors require consideration when using abattoir data for quantitative disease surveillance. Data pertaining to lungs condemned for pneumonia did not provide useful information for predicting disease events, while partial carcass condemnations of nephritis were most consistent with expected trends. Techniques that adjust for non-disease factors should be considered when applying cluster detection methods to abattoir data.

Immunology of porcine circovirus type 2 (PCV2)

The emergence of porcine circovirus type 2 (PCV2) associated diseases and particularly postweaning multisystemic wasting syndrome (PMWS) was a shock for the swine industry and formulated a considerable challenge for researchers in the area of viral immunology in swine. The unique features of PMWS of which emaciation and lymphoid depletion were the most evident indicated a deep involvement of the immune system of the pig in the pathogenesis of this condition and indicated that PCV2 was a singular pathogen. Also, the multifactorial nature of the disease complicated the understanding of PMWS pathogenesis. Nowadays, it is known that PCV2 deeply affects the functionality of the immune system of the pig but also the industry has been able to produce efficacious vaccines. In the present paper some of the most relevant immunological features of PMWS and of PCV2 infection in general will be reviewed.

Concurrent infections are important for expression of porcine circovirus associated disease

Porcine circovirus type 2 (PCV2) is the essential component of porcine circovirus disease (PCVD) as the disease syndrome is referred to in Europe and porcine circovirus associated disease (PCVAD) as it is referred to in North America. Singular PCV2 infection rarely results in clinical disease; however, PCVAD is often accelerated in onset, enhanced in severity and prolonged in duration by concurrent viral or bacterial infections. Due to its effect on the immune system, PCV2 has also been shown to enhance protozoal, metazoal, and fungal infections. Several retrospective or cross-sectional studies have investigated the presence and prevalence of various infectious agents associated with PCVAD under field conditions. Experimental models confirm that PCV2 replication and associated lesions can be enhanced by concurrent infection with other viruses or bacteria. The exact mechanisms by which concurrent pathogens upregulate PCV2 are unknown. Co-infections may promote PCV2 infection by increasing immune host cell replication and accumulation in tissues thereby enhancing targets for PCV2 replication. It has also been proposed that co-infections interfere with PCV2 clearance by alteration of cytokine production and profiles. The outcome of differences in timing of co-infections in PCV2-infected pigs is also likely very important and is an area where more research is needed. Given the current knowledge base, it is important that veterinarians do a thorough diagnostic investigation on herds where PCVAD is a recurrent problem in order to implement the most appropriate and cost effective intervention strategies.

Immunisation of pigs with a major envelope protein sub-unit vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) results in enhanced clinical disease following experimental challenge

Disease exacerbation was observed in pigs challenged with virulent porcine reproductive and respiratory syndrome virus (PRRSV) following immunisation with a recombinant GP5 sub-unit PRRSV vaccine (rGP5) produced in E. coli. Eighteen animals were divided into three experimental groups: group A were immunised twice IM with rGP5, 21 days apart; group B acted as positive controls (challenged but not immunised); and group C were negative controls. Pigs in groups A and B were challenged 21 days after the second immunisation of the group A animals. Following challenge, three pigs given rGP5 exhibited more severe clinical signs than the positive controls, including respiratory distress and progressive weight-loss. Although not statistically significant, the more severe disease exhibited by group A animals may suggest previous immunisation as a contributory factor. The mechanisms of these findings remain unclear and no association could be established between the severity of disease, non-neutralising antibody concentrations and tissue viral loads.

Farm level risk factors associated with severity of post-weaning multi-systemic wasting syndrome

A cross-sectional study involving 147 pig farms across England was conducted in 2008-2009. Farm severity of post-weaning multi-systemic wasting syndrome (PMWS) was estimated through the use of an algorithm that combined data on post-weaning mortality, PMWS morbidity and proportion of porcine circovirus type 2 PCR positive pigs. Farms were classified as non/slightly, moderately or highly affected by PMWS. Data on potential PMWS risk factors were collected through interviews, on-farm assessment and serological sampling. Risk factors were identified using multivariable ordinal logistic regression and multivariable linear regression. Factors associated with increased PMWS severity were rearing growers indoors (OR=23.7), requiring a higher number of veterinarian visits per year (OR=9.6), having poorly isolated hospital pens (OR=6.4), buying replacement boars (OR=4.8) and seropositivity to Mycoplasma hyopneumoniae (OR=4.29); factors associated with decreased PMWS severity were low stocking density for growers (OR=0.07), adjusting diets at least three times between weaning and 14 weeks of age (OR=0.12), and requiring visitors to be at least 2 days pig free (OR=0.14). This study provides evidence of the association between environmental and management factors and PMWS severity, and suggests that other pathogens may be important co-factors for the disease. In addition, this study highlights the potential efficacy of biosecurity measures in the reduction/prevention of within-farm PMWS severity.

Absence of porcine circovirus type 1 (PCV1) and high prevalence of PCV 2 exposure and infection in swine finisher herds

Porcine circovirus (PCV) appeared in 1974 as an unidentified, innocuous viral inhabitant of cell cultures and pigs. Today PCV1 is a contaminant of some human vaccines, and PCV2 is a major pathogen of swine. PCV1 is reportedly ubiquitous in swine but nonpathogenic. Since the interplay of PCV1 and PCV2 in swine might explain variable disease results and shed light on the potential for human exposure, we analyzed in depth the prevalence of PCV1 and PCV2 infection and exposure in the U.S. finishing swine herd. Over 82% of sera from 185 farms were positive for PCV2 by PCR, whereas only 2.4% were positive for PCV1. More than 80% of PCV2 DNA-positive swine were also positive for anti-PCV2 antibodies. PCV1 was only rarely present. Exposure of swine, and therefore humans via pigs, to PCV1 is negligible. We conclude that PCV2 causes a persistent infection in pigs and that PCV1 is absent or rare in swine.

Distribution and characterization of IL-10-secreting cells in lymphoid tissues of PCV2-infected pigs

Distribution and characterization of interlukin-10 (IL-10)-secreting cells in lymphoid tissues of pigs naturally infected with porcine circovirus type 2 (PCV2) were evaluated in accordance with PCV2 antigen detection. After screening a total of 56 pigs showing the symptoms of postweaning multisystemic wasting syndrome (PMWS), 15 pigs were PCV2 positive and 5 pigs, which showed stronger positive signals over multiples tissues were further investigated. This study showed that in PCV2-infected lymphoid tissues, particularly mandibular lymph node, spleen and tonsil, IL-10 expression was mainly localized in T-cell rich areas but rarely in B cell rich areas. IL-10 was highly expressed in bystander cells but rarely in PCV2-infected cells. Elevated IL-10 expression was predominantly associated with T cells, but rarely with B cells or with macrophages. The results of this study provide evidence for the role of IL-10 in chronic PCV2 infection and its relation to PCV2 antigen in affected tissues. Constantly elevated levels of IL-10 lead to immunosuppression in persistent and chronic viral infections. The increased IL-10 expression observed in PCV2 infection in this study suggests that IL-10-mediated immunosuppression may play an important role in the pathogenesis and maintenance of naturally occurring PCV2 infection.

Bronchiolitis obliterans organizing pneumonia in Swine associated with porcine circovirus type 2 infection

Bronchiolitis obliterans organizing pneumonia (BOOP) is a chronic respiratory disease. Although the pathogenesis of BOOP is still incompletely understood, BOOP is responsive to steroids and has a good prognosis. In our five pigs with chronic postweaning multisystemic wasting syndrome (PMWS), typical BOOP lesions were revealed. All five porcine lungs showed typical intraluminal plugs, and porcine circovirus type 2 (PCV2) was identified. They also exhibited similar pathologic findings such as proliferation of type II pneumocytes and myofibroblasts (MFBs), extracellular collagen matrix (ECM) deposition, and fragmentation of elastic fibers. MFBs migration correlative molecules, for instance, gelatinase A, B and osteopontin, appeared strongly in the progressing marginal area of polypoid intraluminal plugs of fibrotic lesion. These molecules colocalized with the active MFBs. Both gelatinase activity and intercellular level of active MFBs were significantly increased (P < .05). Porcine chronic bronchopneumonia leads to BOOP and it is associated with PCV2 persistent infection. Swine BOOP demonstrates similar cellular constituents with human BOOP. Perhaps their molecular mechanisms of pathogenesis operate in a similar way. Thus we infer that the swine BOOP can be considered as a potential animal model for human BOOP associated with natural viral infection. Moreover, it is more convenient to obtain samples.

Comparison of commercial and experimental porcine circovirus type 2 (PCV2) vaccines using a triple challenge with PCV2, porcine reproductive and respiratory syndrome virus (PRRSV), and porcine parvovirus (PPV)

The efficacies of commercial porcine circovirus type 2 (PCV2) vaccines and a live PCV1-2a chimeric vaccine were compared in conventional, PCV2-positive piglets using a PCV2-porcine reproductive and respiratory syndrome virus (PRRSV)-porcine parvovirus (PPV) coinfection challenge model. Seventy-three, 2-week-old pigs were randomized into seven groups including five vaccinated and two control groups. Pigs in the vaccinated groups were vaccinated at 3 weeks (one dose) or at 3 and 6 weeks (two dose) of age. All vaccine regimens tested were effective in reducing naturally occurring PCV2 viremia at 16 weeks of age and after PCV2 challenge, demonstrating the capability of the products to induce a lasting protective immunity despite the presence of PCV2 viremia at the time of vaccination.

A mouse model to study infection against porcine circovirus type 2: viral distribution and lesions in mouse

Background

Little information is known about viral distribution and transmission of porcine circovirus type 2 (PCV2) in species other than swine. It is still a debated topic whether the PCV2 could be infected and caused clinical lesions. Our study is aimed to estimate the susceptibility of Kunming mouse to PCV2. Forty-eight, 6-week-old Kunming mice were randomly divided into four groups. Group A (C1-C12) was inoculated with PK-15 cell culture as a control group. Group B (sPCV1-12) was inoculated orally and intramuscularly with PCV2 (10^6.2TCID₅₀/ml). Group C (mPCV1-12) was inoculated orally and intramuscularly with PCV2 (10^6.2TCID₅₀/ml) and a booster inoculation at days 14 and 28 after the first inoculation. Group D (MixPCV1-12) was unvaccinated but released into Group C. Each group was sacrificed at 7, 14, 28, and 42 days post-inoculation, respectively. Necropsy was checked on every mouse. Sera samples were collected for the test of PCV2 specific antibody. Tissues were collected for histopathology study and polymerase chain reaction (PCR).

Results

The results showed that viral replication, seroconversion, and microscopic lesions were found in inoculated mice. Continuous existence of PCV2 viruses in lymph nodes have been confirmed by PCR, which took at least seven days for the virus to be transferred into other organs from the primary interface, and the diffusion to thymus had been retarded for seven days. Special PCV2 antibody could be found in PCV2 inoculation mice and was significantly higher than that in the control. Further more, microscopic lesions and the main target of PCV2 focused in the lymph nodes with a characteristic depletion and occasional necrosis of lymphocytes in the cortex and paracortex were found in inoculated mice.

Conclusions

The Kunming mouse could be infected by PCV2 virus and used as a PCV2 infected experimental model.

Immunity conferred by an experimental vaccine based on the recombinant PCV2 Cap protein expressed in Trichoplusia ni-larvae

Porcine circovirus type 2 (PCV2) vaccination has been recently included as a measure to control postweaning multisystemic wasting syndrome (PMWS) in the field. Aiming to obtain a more affordable vaccine to be extensively implemented in the field, a highly efficient non-fermentative expression platform based on Trichoplusia ni (T. ni) larvae was used to produce a baculovirus-derived recombinant PCV2 Cap protein (rCap) for vaccine purposes. Vaccination of pigs with rCap induced solid protection against PCV2 experimental infection, inhibiting both the viremia and the viral shedding very efficiently. The protection afforded by the rCap vaccine strongly correlated with the induction of specific humoral immune responses, even in the presence of PCV2-specific maternal immunity, although cellular responses also seemed to play a partial role. In summary, we have shown that rCap expressed in T. ni larvae could be a cost-effective PCV2 vaccine candidate to be tested under field conditions.

Exploratory Epidemiological Study on Porcine Circovirus Type 2 Infection and Postweaning Multisystemic Wasting Syndrome in the Czech Republic

The objective of our study was to diagnose the postweaning multisystemic wasting syndrome (PMWS) and to determine the prevalence of the disease in 33 swine herds in the Czech Republic using the results of laboratory examinations of 100 pigs expressing the signs of wasting at the end of 2007. Microscopic lesions associated with the presence of porcine circovirus 2 (PCV2) antigen were detected in the lymph nodes from 39 of 100 diseased pigs (39%). Based on individual assessment of severity of microscopic lymphoid lesions associated with high amounts of PCV2 antigen, PMWS was confirmed in 4 out of 39 pigs originating from 3 of 33 herds (9%). The epidemiological study indicates that PCV2 infections associated with PMWS disease are only sporadically present in the Czech Republic. Subsequently used real time PCR technique confirmed the relation between PMWS status at the individual pig level and PCV2 DNA concentration. PCV2 DNA load in lymph nodes of PMWS-affected pigs were about 3 logs higher than the levels detected in the PMWS-nonaffected group (P < 0.05). Other parallel viral infections (PRRSV, PPV) were detected by real time PCR techniques in 21 out of 39 PCV2 infected pigs (54%). The results of serological examination of blood samples collected during the necropsy of 100 pigs are suggestive of great prevalence of PCV2 infections in pig herds; nevertheless serum samples collected from individual pigs at a single point in time had a low diagnostic value.

Infection, excretion and seroconversion dynamics of porcine circovirus type 2 (PCV2) in pigs from post-weaning multisystemic wasting syndrome (PMWS) affected farms in Spain and Denmark

Longitudinal case-control studies were performed in post-weaning multisystemic wasting syndrome (PMWS) affected farms from Denmark and Spain using similar designs. Fourteen independent batches of 100-154 pigs per batch were monitored from birth to PMWS outbreak occurrence. Pigs displaying PMWS-like signs and matched healthy cohorts were euthanized during the clinical outbreak. PMWS was diagnosed according to internationally accepted criteria and pigs were classified as: (i) PMWS cases, (ii) wasted non-PMWS cases and (iii) healthy pigs. Porcine circovirus type 2 (PCV2) quantitative PCR (qPCR) and serology techniques were applied to analyse longitudinally collected sera and/or nasal and rectal swabs. Results showed that PCV2 load increased in parallel to waning maternal antibody levels, reaching the maximum viral load concurrent with development of clinical signs. PMWS affected pigs had higher PCV2 prevalence and/or viral load than healthy pigs in all collected samples at necropsy (p<0.0001-0.05) and even in sera and nasal swabs at the sampling prior to PMWS outbreak (p<0.01-0.05). Danish farms had a higher PCV2 prevalence in young piglets as well as an earlier PMWS presentation compared to Spanish farms. PMWS diagnoses were confirmed by laboratory tests in only half of pigs clinically suspected to suffer from PMWS. Positive and significant correlations were found among PCV2 viral loads present in sera, nasal swabs, rectal swabs and lymphoid tissues (R=0.289-0.827, p<0.0001-0.01), which indicates that nasal and rectal swabs were suitable indicators of PCV2 excretion. Sensitivity and/or specificity values observed from both tests used separately or combined suggested that qPCR and/or serology tests are not apparently able to substitute histopathology plus detection of PCV2 in tissues for the individual PMWS diagnosis within PMWS affected farms. However, qPCR appears to be a potential reliable technique to diagnose PMWS on a population basis.

Porcine circoviruses: a minuscule yet mammoth paradox

Porcine circovirus type 2 (PCV2) is the primary causative agent for porcine circovirus-associated disease (PCVAD). PCVAD has been the cause of considerable economic losses to the pork industry worldwide. The disease is primarily characterized by wasting, enlarged lymph nodes, jaundice and weight loss in affected weanling pigs. Several other complex syndromes involving reproductive failure, enteritis, pneumonia and necrotizing dermatitis have also been associated with PCV2 infection. Lymphoid depletion, which is the hallmark lesion of PCVAD, predisposes the host to immunosuppression. Disease progression is further complicated by co-infections with other bacterial and viral pathogens. Despite the availability of effective vaccines for the last 2 years, newly emerging strains of the virus have been reported to cause more severe outbreaks in parts of the USA and Canada. While knowledge of the biology and pathogenesis of PCV2 has progressed considerably over the last 12 years since the disease was recognized, many questions still remain to be answered.

Perfil sorológico para circovírus suíno tipo 2 em granjas comerciais de suínos no Brasil

A técnica de imunoperoxidase em monocamada de células (IPMC) para demonstração de anticorpos contra o circovírus suíno tipo 2 (CVS2) foi empregada para a investigação sorológica em oito granjas de suínos destinadas à produção comercial. Das 240 amostras de soros testadas, 229 (95,4%) foram reagentes com títulos que variaram de 20 até 10.240. Títulos de anticorpos foram detectados nas faixas etárias de duas a três semanas até animais acima de 24 semanas e encontrados em granjas com e sem a síndrome multissistêmica do definhamento (SMD). A média dos títulos de anticorpos revelou diferenças estatísticas (P<0,05) nas faixas etárias de 11 a 13 e 14 a 22 semanas nos animais oriundos de granjas com e sem a SMD. Os resultados refletem a importância de conhecer o perfil sorológico do rebanho e assegurar a implantação de um efetivo cronograma de vacinação contra o CVS2.

Characterization of interstitial nephritis in pigs with naturally occurring postweaning multisystemic wasting syndrome

Kidney samples with interstitial nephritis from 26 pigs affected by postweaning multisystemic wasting syndrome (PMWS) were selected. A histologic evaluation was carried out to describe the type of inflammation and its relationship with viral load, as assessed by in situ hybridization (ISH). Of 26 cases, 10 revealed a tubulointerstitial, lymphoplasmacytic nephritis, 11 an interstitial granulomatous nephritis, and 5 both types of inflammation (mixed type). In 4 cases of granulomatous inflammation, the pattern was not classically nodular, and a population of macrophages and lymphocytes was present (interstitial lymphohistiocytic nephritis). ISH confirmed the presence of porcine circovirus type 2 (PCV2) nucleic acid in all cases. The epithelium of the renal tubules was the most constantly ISH-positive structure. In tubulointerstitial nephritis, the higher the number of positive inflammatory cells, the more severe the inflammation. The ISH reaction was more heterogeneous and unpredictable in granulomatous nephritis, with some epithelioid and giant cells positive by ISH. To quantify macrophages distributed in the three patterns of nephritis, immunohistochemical methods using anti-major histocompatibility complex II (anti-MHC-II) and anti-lysozyme antibodies were undertaken, and semiquantitative evaluation was carried out. MHC-II was mainly expressed by lymphocytes in tubulointerstitial nephritis, but did not always stain macrophages in cases of granulomatous (including lymphohistiocytic) nephritis; the anti-lysozyme antibody revealed macrophages when present in tissues. The amount of PCV2 nucleic acid was not apparently associated with the pattern of inflammation (tubulointerstitial or granulomatous). PCV2 load seems to reflect the severity of the lymphoplasmacytic inflammation but not that of granulomatous and lympho histiocytic types.

Transmission of porcine circovirus 2 (PCV2) by semen and viral distribution in different piglet tissues

Porcine circovirus infections are caused by the porcine circovirus 2 (PCV2). Among six different clinical manifestations involving respiratory, enteric, nervous and reproductive signs, the postweaning multisystemic wasting syndrome (PMWS) is the most important and studied disease. However, reproductive failures associated with PCV2 have been increasingly reported. Some studies have shown the possible contamination of sows by semen of PCV2 positive boars. In order to investigate the transmission of PCV2 by contaminated semen and its ability to infect the sow and piglets, 20 PCV2 negative sows were inseminated, 10 with negative boar semen and 10 with previously nested-PCR tested positive boar semen. The sows were weekly monitored and blood samples were collected. Based on the results, 4 out 20 sows were selected (1 sow was PCR negative and inseminated with a negative semen, 2 sows were PCR negative and inseminated with a positive semen and 1 sow was PCR negative and inseminated with a positive semen, but became PCR positive around the 30 days of pregnancy). After weaning, 12 male piglets, 3 of each sow, were selected and maintained under isolation. In order to investigate which organs harbored the virus, the young pigs were necropsied around 9 months of age. Samples of serum collected monthly were tested by immunocitochemistry (ICC), and all 12 pigs serum converted. Samples of lymphoid, systemic and reproductive organs were analyzed by nested-PCR and immunohistochemistry (IHC). Evaluation of the samples by nested-PCR, revealed that several tissues were positive in 10 of 12 pigs, mainly the lymph nodes, bone marrow and spleen. Various samples were positive by IHC in 8 of 12 piglets, being the lymph nodes, tonsils and bulbourethral glands the most frequently positive. Thus, the results of testing different samples, in the 3 tests (ICC, nested-PCR and IHC) were complementary. These results show that PCV2 transmission through semen to the sows and piglets may occur and may also represent a potential risk for the herd.

The effect of vaccination against porcine circovirus type 2 in pigs suffering from porcine respiratory disease complex

A field study was conducted to investigate the effect of vaccination against porcine circovirus type 2 (PCV2) in pigs suffering from porcine respiratory disease complex (PRDC). A total of 1542 pigs were allocated randomly into two treatment groups at approximately 20 days of age. Groups received either a Baculovirus-expressed recombinant PCV2 Open Reading Frame (ORF) 2 vaccine or placebo by single intramuscular injection. Median onset of PCV2 viraemia and respiratory signs occurred when animals were 18 weeks old. Vaccination reduced the mean PCV2 viral load by 55-83% (p < 0.0001) and the mean duration of viraemia by 50% (p < 0.0001). During the period of study (from 3 to 25 weeks of age) vaccinated animals exhibited a reduced mortality rate (6.63% vs. 8.67%, difference -2.04%; p = 0.1507), an improved average daily weight gain (649 g/day vs. 667 g/day; difference +18 g/day; p < 0.0001) and a reduced time to market (164.8 days vs. 170.4 days; difference -5.6 days; p < 0.0001). The effects on performance were greatest in the 8-week period between the onset of PCV2 viraemia and the end of finishing. These data demonstrate that vaccination against PCV2 alone can significantly improve the overall growth performance of pigs in a multi-factorial, late occurring disease complex such as PRDC.

Ontogeny of systemic cellular immunity in the neonatal pig: Correlation with the development of post-weaning multisystemic wasting syndrome

The aetiology of porcine post-weaning multisystemic wasting syndrome (PMWS) is poorly understood. Porcine circovirus type 2 (PCV-2) is an essential component of the experimental disease model for PMWS: however, evidence from experimental and field studies indicates that additional factors play a critical role in the aetiopathogenesis of PMWS. Current candidates include (1) immune stimulation (for example, via co-infection or vaccination), and (2) a novel infectious agent. A prospective, longitudinal case-control study was designed to investigate molecular triggers in leucocytes of neonatal piglets that may predispose to the development of PMWS. Blood samples were collected weekly from pigs (n=125) within five farms, from 1 week to 8 weeks of age: that is, before the appearance of clinical signs. Four colour flow cytometry was used to investigate changes in subsets of peripheral blood mononuclear cells, using monoclonal antibodies against the following cell associated markers; sIgG, CD3, MHCII dR, CD14, CD4a, CD8a, CD45RC, CD25, SWC3a, SWC8, CD163 and CD45. Sampling and laboratory analysis was supported by monitoring of clinical signs from 1 week to 20 weeks of age, or until disease supervened. At the conclusion of the study, 68 pigs (54%) were classified in Group 1 (no signs of clinical disease), 34 pigs (27%) in Group 2 (signs of clinical disease but not characteristic of PMWS), 17 pigs (14%) in Group 3 (suspect PMWS case) and 5 pigs (4%) in Group 4 (PMWS case). A single case of Porcine Dermatitis and Nephropathy syndrome (PDNS) was also diagnosed. Significant changes with age were demonstrated in clinically normal, neonatal pigs (Group 1), including an increase in B-cells and T-cells, and an increase in the proportion of total T-cells expressing MHCII. Within the T-cell subset, the proportion of CD8(+high) CD4(-) T-cells increased, in addition to the proportion of CD4(+) T-cells co-expressing CD8. Of the factors recorded, farm was found to have a highly significant effect on immune system development in the neonate. Comparison of Groups 1 and 4 cases identified significant differences between pigs which remained normal and those which subsequently developed PMWS. Pigs which went on to develop PMWS had a greater proportion of T-cells expressing MHCII in early life, higher mean intensity of expression of MHCII on T-cells, higher mean intensity of expression of MHCII on B cells and higher expression of CD25 on CD45RC(-) T-cells. These findings suggest that lymphocyte activation may be a key early event in the aetiology of PMWS.