Porcine Circovirus Type 2 Antibodies Research Articles

Expression of human CD46 has no effect on porcine circovirus type 2 infection and shedding in the experimental pig model

Xenotransplantation of tissues from transgenic pigs with desired genetic modifications such as CD46 expression help minimize xenograft rejections. However, CD46 is a known receptor for some viruses. In this study, pigs transgenic for human CD46 (CD46-TG) and appropriate non-transgenic (non-TG) control pigs were utilized to determine possible differences in the level of replication and shedding of porcine circovirus type 2 (PCV2). Non-TG and CD46-TG were blocked by transgenic status and randomly divided into three groups: Non-TG negative controls (n = 3), non-TG-PCV2 (n = 10; PCV2a = 5, PCV2b = 5), and CD46-TG-PCV2 (n = 6; PCV2a = 3, PCV2b = 3). Blood, oral, nasal and fecal swabs were collected at regular intervals from the day of arrival until 70 days post inoculation (DPI). All samples were tested by quantitative real-time PCR for the presence of PCV2 DNA and serum was tested for presence of PCV2 antibodies by ELISA. Overall, the main effects "transgenic status" and "PCV2 subtype" had no influence on degree of PCV2 viremia and shedding or the anti-PCV2 humoral immune response in CD46-TG-PCV2 pigs compared to non-TG-PCV2 pigs. Differences in PCV2 concentrations between non-TG-PCV2 and CD46-TG-PCV2 pigs were minimal and limited to DPI 35 in sera, DPI 7 in fecal swabs and DPI 5 in nasal swabs when CD46-TG-PCV2 pigs had significantly higher concentrations of PCV2 DNA. At DPI 1, CD46-TG-PCV2 pigs had significantly lower concentrations of PCV2 DNA in oral swabs. Under the study conditions, the presence of human CD46 in transgenic pigs had no effect on PCV2 infection in otherwise healthy pigs capable of a normal immune response.

Genetic line influences pig growth rate responses to vaccination for porcine circovirus type 2

Objectives: To compare the effects of porcine circovirus type 2 (PCV2) vaccination on growth rate, backfat depth, and loin depth of pigs in a high-health herd which contained different genetic lines. Materials and methods: A total of 454 pigs (20.6 ± 1.98 days of age; 6.1 ± 1.27 kg body weight) were used in a 130-day randomized controlled field trial. Genetic designations were A×A (Duroc line), B×B (synthetic White Pietrain line), A×B, and B×A. Pigs were randomly assigned to vaccination treatments (Vaccinated or nonvaccinated Control) within litter by gender (boar or gilt). Vaccinated pigs received two doses of a PCV2 vaccine at 3 and 5 weeks of age. Serum samples were collected and pigs were individually weighed on Days 0 (weaning), 40, and 130 to determine PCV2 viral load, antibody levels, and average daily gain (ADG). Data were analyzed from 417 pigs with complete growth records. Results: The greater ADG from Day 0 to Day 130 for Vaccinated pigs depended on the genetic line (genetic line-by-vaccination interaction; P < .05). The mean weight difference between Vaccinated and Control pigs was almost four times greater in the A×A pigs than in the B×B pigs on Day 130. On average, compared with Control pigs, Vaccinated pigs had lower serum PCV2 viral load levels on Days 40 and 130 (P < .001). Implications: Pig genetic line affects growth rate response to PCV2 vaccination and should be considered a risk factor for circoviral disease expression.

Age-dependent susceptibility to porcine circovirus type 2 infections is likely associated with declining levels of maternal antibodies

Objectives: To investigate the relationships between age, porcine circovirus type 2 (PCV2) viremia, and pathologic lesions by evaluating the age of porcine circovirus associated disease- (PCVAD-) affected pigs submitted to Iowa State University Veterinary Diagnostic Laboratory between 2003 and 2010 and by experimentally infecting pigs of different ages. Materials and methods: A total of 3565 PCVAD cases were selected and ages of PCVAD-affected pigs summarized. Sixty-two pigs were randomly assigned to three groups and inoculated with PCV2 at 2 weeks (AGE-2; n = 21), 7 weeks (AGE-7; n = 20), or 12 weeks of age (AGE-12; n = 21). A portion of the pigs in each group arbitrarily selected by the farm manager were vaccinated with an adjuvanted vaccine (Mycoplasma hyopneumoniae) at 1 week of age. All pigs were euthanized 14 days post inoculation (DPI). Lesions and viremia were compared among groups. Results: Among PCVAD cases received from 2003 to 2010, 47.6% were 12 to 16 weeks of age. AGE-12 pigs had significantly lower levels of PCV2 antibody compared with AGE-2 and AGE-7 pigs at the time of inoculation, and AGE-12 pigs had significantly higher levels of PCV2 viremia at 7 and 14 DPI. Mycoplasma hyopneumoniae-vaccinated pigs in the AGE-12 group had higher levels of PCV2 viremia compared to nonvaccinated pigs; however, this effect was not seen in younger pigs. Implications: Under field conditions, 12- to 16-week-old pigs are most commonly affected by PCVAD. Under experimental conditions, 12-week-old pigs are more susceptible to PCV2 infection than are 2- and 7-week-old pigs.

Commercially produced spray-dried porcine plasma contains increased concentrations of porcine circovirus type 2 DNA but does not transmit porcine circovirus type 2 when fed to naïve pigs

The porcine circovirus type 2 (PCV2) antibody and DNA status of porcine plasma products collected during the commercial spray-drying process were evaluated. Samples evaluated included 52 pooled liquid plasma (fresh) samples collected at 14 regional abattoirs before transport to 1 of 2 spray-drying facilities, 32 pooled liquid plasma (concentrated) samples collected after arrival at the spray-drying facilities at different stages before the spray-drying process, and 32 samples in powdered form (spray-dried) collected after spray drying. All 116 samples were positive for PCV2 antibody, with PCV2 ELISA sample-to-positive ratios ranging from 9.2 to 13.6 on a DM basis. Porcine circovirus type 2 DNA (4.5 to 7.9 log(10) PCV2 copies/mL, DM basis) was present in 82.7% (43/52) of the fresh plasma samples, 71.9% (23/32) of the concentrated plasma samples and 78.1% (25/32) of the spray-dried plasma samples, with a greater prevalence of PCV2b than PCV2a. To determine the infectivity of PCV2 DNA-positive commercial spray-dried plasma, nine 10-wk-old 68-kg PCV2-naïve pigs were randomly assigned to 1 of 3 treatment groups and rooms: 1) a negative control (no plasma in the feed, not inoculated with PCV2); 2) a positive control (no plasma in the feed, inoculated with PCV2); and 3) plasma-fed pigs (4% porcine plasma in the feed for 42 d, not inoculated with PCV2). All positive control pigs became viremic by 7 d postinoculation and seroconverted by 42 d postinoculation, whereas pigs in the negative control group and in the spray-dried plasma group were PCV2 PCR negative and did not seroconvert to PCV2 for the duration of the study. The results indicate that PCV2 DNA and antibodies are commonly found in commercial spray-dried plasma. However, no evidence of infectivity of the PCV2 DNA was found in naïve pigs when commercial spray-dried plasma was included in the diet under the conditions of this study.

Reproductive Losses Associated with Porcine Circovirus Type 2 in a Japanese Herd of Seronegative Sows

From April to July 2009, there was a high rate of reproductive losses in a 30-sow, farrow-to-finish swine herd in Yamagata Prefecture, Japan. Histopathological examinations of heart tissue from stillborn and preweaning piglets showed nonsuppurative, necrotizing lesions. Immunohistochemical staining and polymerase chain reaction analysis of myocardial lesions revealed the presence of porcine circovirus type 2 (PCV2) antigens and DNA in these tissues. Indirect immunofluorescence also showed that the PCV2 antibody positive rate in the sows was higher in May 2009 than in December 2008. The results of this study suggest that PCV2 spread to this farm and caused a high rate of reproductive losses.

Effect of vaccination of boars against porcine circovirus type 2 on ejaculate characteristics, serum antibody titers, viremia, and semen virus shedding1

The objective of this research was to determine the effect of vaccination against porcine circovirus type 2 (PCV2) on ejaculate characteristics, PCV2-specific antibody titers in serum, viremia, and viral shedding in the semen of PCV2-positive boars. Before vaccination, all boars were confirmed by PCR to be naturally infected with PCV2. The boars were vaccinated with a commercial killed vaccine against PCV2 (n = 5) or served as controls and received 2 mL of 0.9% saline (n = 5). Semen and blood samples were collected before vaccination at wk 0 and at 7-d intervals thereafter until wk 8. Sperm concentration and characteristics of sperm motility were assessed using a computer-assisted sperm analysis system, and sperm morphology was evaluated using light microscopy after staining. The PCV2 antibody titers were determined in serum using an ELISA, and the genomic copy numbers of PCV2 DNA in serum and semen were determined by real-time PCR. In general, there were no effects of treatment or treatment × week on semen or sperm characteristics (P > 0.10). An effect of treatment × week was detected for serum antibody titers (P < 0.01). Compared with controls, PCV2 antibody titers in vaccinated boars were less (P < 0.01) at wk 7 (1.01 ± 0.05 titer/mL vs. 1.23 ± 0.05 titer/mL) and tended (P = 0.07) to be less at wk 8 (1.05 ± 0.05 titer/mL vs. 1.17 ± 0.05 titer/mL). There were no effects of treatment or treatment × week for serum and semen genomic copy numbers of PCV2 DNA (P > 0.10). There was a tendency (P = 0.09) for an effect of week on serum viral load. It was evident that during this experiment, boars experienced reoccurring PCV2 infection, and the detection of an increased PCV2 DNA load in serum preceded that in semen; the duration of reoccurring infection appeared to be less in vaccinated boars compared with controls. In summary, vaccination against PCV2 can reduce antibody titers when given postinfection and has no dramatic effect on indicators of semen quality. Vaccination against PCV2 in naturally infected boars can also decrease the length of reoccurring infection and decrease the duration of viral shedding in semen.

A cohort study of post-weaning multisystemic wasting syndrome and PCV2 in 178 pigs from birth to 14 weeks on a single farm in England

Our hypothesis was that pigs that develop post-weaning multisystemic wasting syndrome (PMWS) are detectable from an early age with signs of weight loss and other clinical and serological abnormalities. Therefore, the objective of this study was to investigate the temporally varying and fixed events linked with the clinical incidence of PMWS by comparing affected and unaffected pigs in a cohort of 178 male piglets. Piglets were enrolled at birth and examined each week. Samples of blood were collected at regular intervals. The exposures measured were porcine circovirus type 2 (PCV2) antibody titres in all 178 and PCV2 antigen in a subset of 75 piglets. We also observed piglet health and measured their weight, and a post-mortem examination was performed by an external laboratory on all pigs between 6 and 14 weeks of age that died. From the cohort, 14 (8%) pigs died from PMWS and 4% from other causes. A further 37 pigs between 6 and 14 weeks of age died from PMWS (30) and ileitis and other causes (7). PMWS was only apparent in pigs from 1 to 2 weeks before death when they wasted rapidly. There were no other characteristic clinical signs and no obvious gross clinical lesions post-mortem. There was no strong link with PCV2 antibody throughout life but PCV2 antigen level was higher from 4 to 6 weeks of age in pigs that died from PMWS compared with pigs that died from other causes.

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

BackgroundLittle 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 (106.2TCID50/ml). Group C (mPCV1-12) was inoculated orally and intramuscularly with PCV2 (106.2TCID50/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).ResultsThe 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.ConclusionsThe Kunming mouse could be infected by PCV2 virus and used as a PCV2 infected experimental model.

An ELISA based on a truncated soluble ORF2 protein for the detection of PCV2 antibodies in domestic pigs

Postweaning multisystemic wasting syndrome (PMWS) is an important swine disease that is closely associated with porcine circovirus type 2 (PCV2). The capsid protein (Cap protein) is a major structural protein that has at least three immunoreactive regions, and it can be a suitable candidate antigen for detecting the specific antibodies of a PCV2 infection. In the present study, an indirect enzyme-linked immunosorbent assay (TcELISA) based on a truncated soluble Cap protein produced in Escherichia coli (E.coli) was established and validated for the diagnostic PCV2 antibodies in swine. The TcELISA was validated by comparison with an indirect immunofluorescence assay (IIFA). The diagnostic sensitivity (DSN), specificity (DSP), and accuracy of the TcELISA were 88.6%, 90.7% and 89.4%, respectively. The agreement rate was 89.38% between results obtained with TcELISA and IIFA on 113 field sera. A cross-reactivity assay showed that the method was PCV2-specific by comparison with other sera of viral disease. Therefore,the TcELISA will be helpful for the development of a reliable serology diagnostic test for large scale detection of PCV2 antibodies and for the evaluation of vaccine against PCV2 in swine.

Selected Swine Viral Pathogens in Indoor Pigs in Spain. Seroprevalence and Farm-Level Characteristics

A serosurvey on porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), Aujeszky's disease virus gE protein (ADV gE), porcine parvovirus (PPV) and porcine circovirus type 2 (PCV2) was carried out in Spanish pig herds. The serosurvey consisted of two studies. First, a retrospective study assessed the proportion of seropositive boar, sow and fattening pig herds and their seroprevalences to PRRSV, SIV, ADV gE and PPV from 2003 to 2005 and to PCV2 from 2000 to 2005. Such information was obtained from routine serologic analyses from two veterinary diagnostic laboratory services. Second, a cross-sectional study in sow and fattening pig herds from 44 farms (without vaccination interferences on serologic analyses) was performed to provide information on seroprevalences and co-seropositivity to PRRSV, SIV, ADV gE and PCV2 (PPV was excluded because of widespread vaccination) and to elucidate their relationships with farm characteristics, management and productive parameters. Similar seroprevalences were observed in both studies, although some variations were obtained, probably because of vaccination schedules, number of tested sera, sampling age and regional variations. Percentage of PRRSV and SIV seropositive herds was over 85% for sows, around 80% for fatteners and around 50% for boar studs. The proportion of ADV gE seropositive sow herds decreased from 41% to 30% between 2003 and 2005, whereas such decrease was from 41% to 33% in fattening pig herds and from 13% to 4% in boar studs PCV2 antibodies were widespread as well as those against PPV; in the latter case, if antibodies were elicited by infection and/or vaccination was not assessed. Concurrent presence of PCV2, PRRSV and SIV antibodies was found in 89% and 66% sow and fattening herds, respectively. No statistical associations were obtained between seroprevalences or co-seropositivity and farm characteristics, management or productive parameters.

Dynamics of serum antibodies to and load of porcine circovirus type 2 (PCV2) in pigs in three finishing herds, affected or not by postweaning multisystemic wasting syndrome

BackgroundDespite that PMWS commonly affects pigs aged eight to sixteen weeks; most studies of PMWS have been conducted during the period before transfer to finishing herds. This study focused on PCV2 load and antibody dynamics in finishing herds with different PMWS status.MethodsSequentially collected blood samples from 40 pigs in each of two Swedish (A and B) and one Norwegian (C) finishing herds were analysed for serum PCV2-load and -antibodies and saliva cortisol. The two Swedish herds differed in PMWS status, despite receiving animals from the same sow pool (multi-site production). However, the PMWS-deemed herd (A) had previously also received pigs from the spot market. ResultsThe initial serum PCV2 load was similar in the two Swedish herds. In herd A, it peaked after two weeks in the finishing herd and a high number of the pigs had serum PCV2 levels above 107 per ml. The antibody titres increased continually with exception for the pigs that developed PMWS, that had initially low and then declining antibody levels. Pigs in the healthy herd B also expressed high titres of antibodies to PCV2 on arrival but remained at that level throughout the study whereas the viral load steadily decreased. No PCV2 antibodies and only low amounts of PCV2 DNA were detected in serum collected during the first five weeks in the PMWS-free herd C. Thereafter a peak in serum PCV2 load accompanied by an antibody response was recorded. PCV2 from the two Swedish herds grouped into genotype PCV2b whereas the Norwegian isolate grouped into PCV2a. Cortisol levels were lower in herd C than in herds A and B.ConclusionsThe most obvious difference between the Swedish finishing herds and the Norwegian herd was the time of infection with PCV2 in relation to the time of allocation, as well as the genotype of PCV2. Clinical PMWS was preceded by low levels of serum antibodies and a high load of PCV2 but did not develop in all such animals. It is notable that herd A became affected by PMWS after errors in management routine, emphasising the importance of proper hygiene and general disease-preventing measures.

Possible pathogenic interplay between Chlamydia suis, Chlamydophila abortus and PCV-2 on a pig production farm

A concurrent outbreak of chlamydial disease in boars, sows and gilts and postweaning multisystemic wasting syndrome (PMWS) in weaned piglets was investigated on a large pig production farm in Estonia....

The open reading frame 3 (ORF3) of porcine circovirus type 2 (PCV2) is dispensable for virus infection but evidence of reduced pathogenicity is limited in pigs infected by an ORF3-null PCV2 mutant

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases (PCVAD) in pigs. The open reading frame (ORF) 3 of PCV2 reportedly induces apoptosis and is associated with PCV2 pathogenicity. In this study, we first created an ORF3-null PCV2 mutant (muPCV2) by site-directed mutagenesis and demonstrated that the dimerized plasmid DNA of muPCV2 clone is infectious when injected intramuscularly (I.M.) into pigs. Subsequently, by using a well-characterized pig model we compared the pathogenicity of the muPCV2 and the wildtype PCV2. Thirty-one pigs were divided into 3 groups of 11, 10, and 10 each: group 1 pigs were each inoculated I.M. with PBS buffer as negative controls, group 2 pigs each with 200 μg of muPCV2 infectious DNA clone, and group 3 pigs each with 200 μg of wildtype PCV2 infectious DNA clone. Blood was collected prior to inoculation and weekly thereafter, and tested for PCV2 antibodies by ELISA and serum viral DNA loads by quantitative PCR. All pigs were necropsied at 35 days post-inoculation. The results showed that pigs inoculated with muPCV2 had a delayed seroconversion and lower serum viral load. However, there was no significant difference in the average scores of the histological or gross lesions or the amount of PCV2-specific antigen in tissues between wildtype PCV2- and muPCV2-inoculated groups. Thus, the data from this study do not fully support the conclusion of a previous report regarding PCV2 attenuation by abrogation of ORF3 although the results did show that ORF3 is dispensable for PCV2 replication in pigs.

Effect of natural or vaccine-induced porcine circovirus type 2 (PCV2) immunity on fetal infection after artificial insemination with PCV2 spiked semen

The objectives of this study were to determine if vaccination against porcine circovirus type 2 (PCV2) or previous PCV2 infection of the dam are sufficient to prevent fetal infection when dams are artificially inseminated with PCV2-spiked semen. Nine sows (Sus domestica) were allocated into three groups of three dams each: The PCV2 naïve negative control Group 1 was artificially inseminated with extended PCV2 DNA negative semen during estrus, whereas the extended semen used in the vaccinated Group 2 (PCV2 vaccine was given 8 wk before insemination) and PCV2-exposed Group 3 (infected with PCV2 12 wk before insemination) was spiked with 5 mL of PCV2 inoculum with a titer of 10 4.2 tissue culture infectious dose (TCID 50) per milliliter at each breeding. The dams in the vaccinated and PCV2-exposed groups were positive for PCV2 antibody but negative for PCV2 DNA in serum at the time of insemination. Three negative control dams, two vaccinated dams, and three dams with previous PCV2 exposure became pregnant and maintained pregnancy to term. After artificial insemination, viremia was detected in one of three vaccinated dams and in two of three dams with previous PCV2 exposure. At farrowing, PCV2 infection was not detected in any piglets or fetuses expelled from the negative control dams or from dams with previous PCV2 exposure. In litters of the vaccinated dams, 15 of 24 live-born piglets were PCV2 viremic at birth, with 6 of 26 fetuses having detectable PCV2 antigen in tissues. In conclusion, vaccine-induced immunity did not prevent fetal infection in this sow model using semen spiked with PCV2.

The index herd with PMWS in Sweden: Presence of serum amyloid A, circovirus 2 viral load and antibody levels in healthy and PMWS-affected pigs

BackgroundPostweaning Multisystemic Wasting Syndrome (PMWS) is an emerging disease in pigs of multifactorial origin, but associated to porcine circovirus type 2 (PCV2) infection. PMWS was first diagnosed in Sweden at a progeny test station that received pigs aged five weeks from 19 different nucleus herds on the day after weaning. The objective of this study was to examine, for the first time in an index outbreak of PMWS, the relationship between PCV2 virus, antibodies to PCV2 and serum amyloid a (SAA) in sequentially collected serum samples from pigs with and without signs of PMWS.MethodsForty pigs of the last batch that entered the station at a mean age of 37.5 days were monitored for signs of PMWS during the first 55 days after arrival. Serum was collected on six occasions and analysed for presence of PCV2 DNA and antibodies to PCV2, as well as for levels of SAA.ResultsFour of the pigs (10%) were concluded to have developed PMWS, with necropsy confirmation in three of them. These pigs displayed low levels of maternal antibodies to PCV2, more than 107 PCV2 viral DNA copies per ml serum and failed to mount a serological response to the virus. Starting between day 23 and 34 after arrival, an increase in PCV2 viral load was seen in all pigs, but PCV2 did not induce any SAA-response. Pigs that remained healthy seroconverted to PCV2 as the viral load was increased, regardless of initially having low or high levels of PCV2-antibodies.ConclusionIn this index case of PMWS in Sweden, pigs affected by PMWS were not able to mount a relevant serum antibody response which contributed to the disease progression. The maximal PCV2 virus load was significantly higher and was also detected at an earlier stage in PMWS-affected pigs than in healthy pigs. However, a viral load above 107 PCV2 DNA copies per ml serum was also recorded in 18 out of 34 pigs without any clinical signs of PMWS, suggesting that these pigs were able to initiate a protective immune response to PCV2.

Quantification of porcine circovirus type 2 (PCV-2) within- and between-pen transmission in pigs

PCV-2 within- and between-pen transmission was quantified by estimating the daily transmission rate beta and the basic reproduction ratio (R(0)) using a stochastic SEIR (Susceptible, Exposed, Infectious, Removed) model fitted on experimental data. Within-pen transmission was quantified by using four groups of eight SPF (specific pathogen-free) pigs (four infected and four susceptible pigs having direct contact). Between-pen transmission was studied in two groups of 16 SPF pigs (eight infected and eight susceptible pigs having indirect contact (10 cm distance)). Pigs were monitored twice a week (blood samples) and were tested for PCV-2 antibodies (ELISA test) and viral genome load in sera (real-time PCR). Transmission parameters beta(within) and beta(between) were estimated using a maximum likelihood method and the duration of infectiousness, to compute R(0), was estimated with a parametric survival model. Different assumptions were made to determine the end of infectiousness (seroconversion, seroconversion and decline in viral genome load, permanent infectiousness). R(0[within]) (8.9 (5.1-15.4)) was greater when the end of infectiousness was assumed to be related to both seroconversion and a decline of PCV-2 genome load in sera (average duration of infectiousness = 32 days) compared with only seroconversion as the indicator of recovery (R(0[within]) = 5.5 (3.3-9.0)). Whatever the assumption, between-pen R(0) (0.58 (0.23-1.47)) was always significantly lower than within-pen R(0). Only beta(within) was sensitive to the assumption on end of infectiousness and decreased with increasing duration of infectiousness. These results showed that PCV-2 transmission is influenced by contact structure that appears worth being taken into account in an epidemic model.

A field evaluation of mortality rate and growth performance in pigs vaccinated against porcine circovirus type 2

To evaluate, under field conditions, the effects of a commercial porcine circovirus type 2 (PCV2) vaccine on mortality rate and growth performance in a herd infected with PCV2 that had a history of porcine circovirus disease. Randomized controlled clinical trial. 485 commercial, cross-bred, growing pigs. Prior to weaning, pigs were randomly assigned within litter to a vaccination or unvaccinated control group. Pigs in the vaccination group were given a commercial PCV2 vaccine at weaning and 3 weeks later. Mortality rate was recorded, and pigs were weighed prior to vaccination, when moved from the nursery, and prior to marketing. Infection status was assessed by serologic testing and detection of viral DNA in serum. Compared with control pigs, pigs vaccinated against PCV2 had a significantly lower mortality rate during the finishing phase, significantly higher average daily gain during the finishing phase, and significantly lower likelihood of being lightweight at the time of marketing. For vaccinated pigs, overall mortality rate was reduced by 50% and average daily gain during the finishing period was increased by 9.3%. At the time of marketing, vaccinated pigs weighed an average of 8.8 kg (19.4 lb) more than control pigs, without any difference in days to marketing. Serum PCV2 antibody titers increased in control pigs, and PCV2 DNA was detected, indicating active PCV2 infection. Results suggested that vaccination against PCV2 was effective at reducing mortality rate and improving growth performance among pigs in a herd infected with PCV2.

A survey on porcine circovirus type 2 infection and phylogenetic analysis of its ORF2 gene in Hangzhou, Zhejiang Province, China

Porcine circovirus type 2 (PCV2) is closely related to the postweaning multisystemic wasting syndrome (PMWS). In this study, the pig serum and tissue samples collected from different regions of Hangzhou District in Zhejiang Province of China between 2003 and 2005 were analyzed by enzyme-linked immunosorbent assay (ELISA) for PCV2 antibody and by polymerase chain reaction (PCR) for ORF2 gene. The results show that out of 1250 randomly collected serum samples, 500 sera (40%) were seropositive for PCV2. PCR results demonstrate that Hangzhou PCV2 with more than 50% Chinese PCV2 strains and French PCV2 formed Cluster A. Only one PCV2 from Hangzhou belonged to Cluster B with some other Chinese PCV2 and Netherlands's isolates. Cluster C consisted of PCV2 isolates from China, US, Canada, UK and Germany. The results indicate that the PCV2 infection was widespread in Hangzhou.

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.

Detection of neutralizing antibodies in postweaning multisystemic wasting syndrome (PMWS)-affected and non-PMWS-affected pigs

The notion that postweaning multisystemic wasting syndrome (PMWS)-affected pigs develop an impaired humoral response against porcine circovirus type 2 (PCV2) has been reported in several studies. However, little information is available regarding the presence of neutralizing antibodies (NA) in PCV2-infected pigs and their role in the pathogenesis of the disease. The aim of the present work was to further characterize the humoral response, and in particular the production of NA, in pigs with different PCV2-infection status. Seventy-two conventional pigs from different farms were classified into three groups based on PCV2 infection and clinico-pathological status, namely: PCV2-negative, non-PMWS PCV2-positive and PMWS-affected animals. In addition, 9-week old pigs from an experimental infection (6 controls and 14 PCV2-inoculated pigs) were also studied. NA and total PCV2 antibodies (TA) as well as viral load in serum were determined and correlated with the clinico-pathological status of pigs. Results indicated that PMWS-affected pigs had lower NA titres, if any, than healthy animals. NA titres were also inversely correlated with PCV2 load in serum. NA and TA titres were positively correlated; however, correlation differed among infection status, being lower in PCV2-positive pigs. Also, the diagnostic performance of each test was evaluated, indicating that the combination of viral neutralization and quantitative PCR in serum was useful to discard PMWS (specificity 92%). In experimentally infected animals, the evolution of NA paralleled the course TA, although a slight delay in NA production was seen in some animals. The increase of NA coincided with the drop in viral load. Results from this work further support that PMWS-affected pigs show an impaired humoral immune response and, particularly, an inefficient NA response against PCV2.