No evidence of PEDV infection in French artificial insemination centers in 2015.

Pigs infected by porcine epidemic diarrhea virus (PEDV) are affected by severe diarrhea, vomiting and dehydration. The severity of clinical signs depends on the virus strain. Two genetically different PEDV strains are known to infect pigs, the PEDV S-InDel strains which circulate on all continents and the highly virulent PEDV S-non-InDel strains found in Asia and in America. We have previously demonstrated the presence of PEDV RNA in semen from boars experimentally infected with an S-non-InDel PEDV strain. If naturally infected boars may shed PEDV in semen, this would have important consequences for the breeding sector. Thus we sought to determine whether PEDV has been circulating in populations of breeding boars from French artificial insemination (AI) centers. The current study reports on a serological survey conducted on one hundred and twenty boars from six AI centers, representing 18.6% of the total population of breeding boars in French AI centers in 2015. All of them were found negative for PEDV antibodies, showing no evidence of PEDV circulation in French AI centers at that time.

Factors associated with the growing-finishing performances of swine herds: an exploratory study on serological and herd level indicators.

BACKGROUND: Growing and finishing performances of pigs strongly influence farm efficiency and profitability. The performances of the pigs rely on the herd health status and also on several non-infectious factors. Many recommendations for the improvement of the technical performances of a herd are based on the results of studies assessing the effect of one or a limited number of infections or environmental factors. Few studies investigated jointly the influence of both type of factors on swine herd performances. This work aimed at identifying infectious and non-infectious factors associated with the growing and finishing performances of 41 French swine herds. RESULTS: Two groups of herds were identified using a clustering analysis: a cluster of 24 herds with the highest technical performance values (mean average daily gain = 781.1 g/day +/- 26.3; mean feed conversion ratio = 2.5 kg/kg +/- 0.1; mean mortality rate = 4.1% +/- 0.9; and mean carcass slaughter weight = 121.2 kg +/- 5.2) and a cluster of 17 herds with the lowest performance values (mean average daily gain =715.8 g/day +/- 26.5; mean feed conversion ratio = 2.6 kg/kg +/- 0.1; mean mortality rate = 6.8% +/- 2.0; and mean carcass slaughter weight = 117.7 kg +/- 3.6). Multiple correspondence analysis was used to identify factors associated with the level of technical performance. Infection with the porcine reproductive and respiratory syndrome virus and the porcine circovirus type 2 were infectious factors associated with the cluster having the lowest performance values. This cluster also featured farrow-to-finish type herds, a short interval between successive batches of pigs (≤3 weeks) and mixing of pigs from different batches in the growing or/and finishing steps. Inconsistency between nursery and fattening building management was another factor associated with the low-performance cluster. The odds of a herd showing low growing-finishing performance was significantly increased when infected by PRRS virus in the growing-finishing steps (OR = 8.8, 95% confidence interval [95% CI]: 1.8-41.7) and belonging to a farrow-to-finish type herd (OR = 5.1, 95% CI = 1.1-23.8). CONCLUSIONS: Herd management and viral infections significantly influenced the performance levels of the swine herds included in this study.

Estimation of the diagnostic performance of two ELISAs to detect PCV2 antibodies in pig sera using a Bayesian method.

This study was designed to assess the diagnostic characteristics of two PCV2 ELISAs without a gold standard. Four hundred and sixty-five serum samples from finishing pigs (25 herds) not vaccinated against PCV2 were used. Samples were tested by two ELISAs: an in-house ELISA (I-ELISA) and the commercial SERELISA®PCV2 Ab Mono Blocking kit (S-ELISA). A ROC curve was used to assess the S-ELISA's optimal threshold by taking the I-ELISA as a reference and using the cut-off previously determined by comparison to an cccmonolayer assay (IPMA). This led to an S-ELISA result ≥170 being considered as positive. The sensitivity (Se) and specificity (Sp) of each ELISA were then estimated without a gold standard using a Bayesian approach. The mean Se and Sp values of the I-ELISA were slightly higher than those of the S-ELISA (mean Se I-ELISA=0.90 vs. mean Se S-ELISA=0.86; mean Sp I-ELISA=0.92 vs. mean Sp S-ELISA=0.85). However, the 95% credibility intervals (CI95%) overlapped (Se I-ELISA CI95%=0.85-0.95 vs. Se S-ELISA CI95%=0.82-0.90; Sp I-ELISA CI95%=0.82-0.98 vs. Sp S-ELISA CI95%=0.75-0.94). Both ELISAs appeared to be valuable tools for detecting PCV2 antibodies.

Factors associated with herd-level PRRSV infection and age-time to seroconversion in farrow-to-finish herds.

Factors associated with porcine reproductive and respiratory syndrome virus (PRRSV) infection were investigated in 109 herds. Serums from four batches of pigs (4, 10, 16 and 22 weeks, 15 pigs/batch) were tested by ELISA for PRRSV antibodies. Infection by Mycoplasma hyopneumoniae (Mhp), Actinobacillus pleuropneumoniae, H1N1 and H1N2 swine influenza A viruses (swIAV) and PCV2 were detected by specific serological or PCR tests. Data related to herd characteristics, biosecurity, management housing and climatic conditions were collected during a herd visit. Factors associated with the herd's PRRSV seropositive status were identified by logistic regression. Large herd size, the lack of disinsectisation in the gestation facilities, on-farm semen collection, a short time-period for gilt quarantine and a low temperature setpoint for the ventilation controller in the fattening room significantly increased the odds of a herd being seropositive for PRRSV. Infection by Mhp and H1N2 swIAV were associated with a PRRSV seropositive status. A Cox proportional hazards model was used to identify the factors associated with the age-time to seroconversion in infected herds. Joint housing for the gilts and sows when lactating, a large nursery pen, a small number of pens per fattening room and lack of all-in all-out management in the fattening section significantly reduced the age-time to seroconversion. A small range of temperatures controlling ventilation rate in the nursery room was also associated with time to PRRSV seroconversion. Infection by Mhp and a high PCV2 infection pressure were associated with a shorter time to seroconversion. Biosecurity measures minimising the risk of introducing PRRSV into the herd, management practices reducing contacts between animals from different batches and within batches and favourable climatic conditions should be implemented to better control PRRSV infection.

A commercial PCV2a-based vaccine significantly reduces PCV2b transmission in experimental conditions.

Transmission characteristics of PCV2 have been compared between vaccinated and non-vaccinated pigs in experimental conditions. Twenty-four Specific Pathogen Free (SPF) piglets, vaccinated against PCV2 at 3weeks of age (PCV2a recombinant CAP protein-based vaccine), were inoculated at 15days post-vaccination with a PCV2b inoculum (6⋅10(5) TCID50), and put in contact with 24 vaccinated SPF piglets during 42days post-inoculation. Those piglets were shared in six replicates of a contact trial involving 4 inoculated piglets mingled with 4 susceptible SPF piglets. Two replicates of a similar contact trial were made with non-vaccinated pigs. Non vaccinated animals received a placebo at vaccination time and were inoculated the same way and at the same time as the vaccinated group. All the animals were monitored twice weekly using quantitative real-time PCR and ELISA for serology until 42days post-inoculation. The frequency of infection and the PCV2 genome load in sera of the vaccinated pigs were significantly reduced compared to the non-vaccinated animals. The duration of infectiousness was significantly different between vaccinated and non-vaccinated groups (16.6days [14.7;18.4] and 26.6days [22.9;30.4] respectively). The transmission rate was also considerably decreased in vaccinated pigs (ß=0.09 [0.05-0.14] compared to ß=0.19 [0.11-0.32] in non-vaccinated pigs). This led to an estimated reproduction ratio of 1.5 [95% CI 0.8 - 2.2] in vaccinated animals versus 5.1 [95% CI 2.5 - 8.2] in non-vaccinated pigs when merging data of this experiment with previous trials carried out in same conditions.

Infectious agents associated with respiratory diseases in 125 farrow-to-finish pig herds: a cross-sectional study.

A study was carried out in 125 farrow-to-finish pig herds to assess the relationships between pathogens involved in respiratory disorders and to relate these findings to clinical signs of respiratory diseases and pneumonia and pleuritis at slaughter. Clinical examination and sampling were carried out on four different batches in each herd (pigs aged 4, 10, 16 and 22 weeks). Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, swine influenza viruses (SIV), porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) were detected by serological or PCR tests. Pneumonia-like gross lesions and pleuritis were scored at the slaughterhouse. The results indicate that the percentage of pigs PCR-positive for PCV2 at 4, 10 and 16 weeks old was associated with the percentage of pigs PCR-positive for M. hyopneumoniae at these ages. On the other hand, the percentage of pigs with antibodies against PRRSV at 10, 16 and 22 weeks was positively correlated with the percentage of pigs seropositive for M. hyopneumoniae at 22 weeks, with the percentage of pigs with antibodies against SIV H1N1 and SIV H1N2 and the percentage of pigs sero-positive for A. pleuropneumoniae serotype 2. The findings also indicate that, within the five studied pathogens, M. hyopneumoniae, PRRSV and SIV H1N1 are the major pathogens involved in pneumonia-like gross lesions even though PCV2 may play a role. A. pleuropneumoniae serotype 2, in association with PRRSV, is significantly associated with extensive pleuritis. Respiratory diseases could be significantly reduced by implementing measures including appropriate management practices to control these pathogens.

Influence of husbandry and control measures on porcine circovirus type 2 (PCV-2) dynamics within a farrow-to-finish pig farm: a modelling approach.

We assessed, using a modelling approach, the influence of several management practices within a farrow-to-finish farm on the age of PCV-2 infection. The impact of PCV-2 vaccination with different vaccination schemes on infection dynamics, was also tested. A stochastic individual-based model describing the population dynamics in a typical French farrow-to-finish pig farm was built and coupled with an epidemiological model of PCV-2 infection. The parameters of the infectious model were mainly obtained from previous transmission experiments. Results were subjected to a survival analysis of time-to-infection. For each comparison, the reference situation was no vaccination followed by random mixing of piglets after birth and after weaning. The risk of early infection was significantly reduced when mixing of piglets was reduced at different stages (avoiding cross-fostering and grouping piglets by litters in small pens after weaning, hazard ratio (HR)=0.52 [0.46; 0.59]). Sow-targeted vaccination delayed the infectious process until the waning of passive immunity and piglet-targeted vaccination considerably decreased the force of infection leading to a dramatic decrease of the total number of infections (HR=0.44 [0.37; 0.54]). The effect was even more pronounced when strict management measures were applied (HR=0.24 [0.19; 0.31]). Changing from a low (3%) prevalence of PCV-2-infected semen to a higher one (18%) significantly increased the risk of early infections (HR=1.36 [1.2; 1.53]), whereas reducing replacement rate or changing sow housing from individual crates to group housing had a limited impact on PCV-2 dynamics.

Individual risk factors for Post-weaning Multisystemic Wasting Syndrome (PMWS) in pigs: a hierarchical Bayesian survival analysis.

Risk factors for Post-weaning Multisystemic Wasting Syndrome (PMWS) at the pig level were identified using data from a longitudinal study in seven PMWS-affected farms in France. In each farm, a representative sample of 120 pigs (180 in one farm) was randomly selected after farrowing and followed from birth to slaughter. Individual information included serological status for Porcine Circovirus type 2 (PCV-2), Porcine Reproductive and Respiratory Syndrome (PRRS) virus, and Porcine Parvovirus (PPV), individual weight, rearing conditions, and clinical observations recorded at 7, 13, 16 and 21 weeks of age and at slaughter. Two different Bayesian frailty models were used to identify variables related to time-to-PMWS: (i) a logistic-survival model and (ii) an accelerated failure time model (different survival time distributions) both with two levels of clustering (litter and farm). Similar results in terms of variables related to time-to-PMWS were obtained with both models. However, information provided by the different approaches were complementary. Piglets were more likely to exhibit PMWS after early infection by PCV-2 (i.e. before 7 weeks old) and if they were weaned early (before 21 days). Piglets born to PCV-2 seronegative sows and/or to sows with neck injuries due to poorly performed injections were also more at risk. With the accelerated failure time model, time ratios were obtained giving an estimation of the expected survival time (increased or decreased) after exposure to the factor. The logistic-survival model showed that the majority of the risk factors were mostly related to the odds of PMWS whereas the PCV-2 passive immunity derived from the dam also tended to postpone PMWS appearance later.

Modelling the time-dependent transmission rate for porcine circovirus type 2 (PCV2) in pigs using data from serial transmission experiments.

Six successive transmission trials were carried out from 4 to 39 days post inoculation (DPI) to determine the features of the infectious period for PCV2-infected pigs. The infectiousness of inoculated pigs, assessed from the frequency of occurrence of infected pigs in susceptible groups in each contact trial, increased from 4 to 18 DPI (0, 7 and 8 infected pigs at 4, 11 and 18 DPI, respectively) and then decreased slowly until 39 days post infection (4, 2 and 1 pigs infected at 25, 32 and 39 DPI, respectively). The estimated time-dependent infectiousness was fitted to three unimodal function shapes (gamma, Weibull and lognormal) for comparison. The absence of infected pigs at 4 DPI revealed a latency period between 4 and 10 DPI. A sensitivity analysis was performed to test whether the parametric shape of the transmission function influenced the estimations. The estimated time-dependent transmission rate was implemented in a deterministic SEIR model and validated by comparing the model prediction with external data. The lognormal-like function shape evidenced the best quality of fit, leading to a latency period of 8 days, an estimated basic reproduction ratio of 5.9 [1.8,10.1] and a mean disease generation time of 18.4 days [18.2, 18.5].

Post-weaning multisystemic wasting syndrome and other PCV2-related problems in pigs: a 12-year experience.

Post-weaning multisystemic wasting syndrome (PMWS) and other porcine circovirus type 2 (PCV2)-related diseases have been reported throughout the world for about 10 years. The present paper reviews the knowledge acquired in different fields and is largely based on the authors' experience. The horizontal transmission of PCV2 is widely documented. Contact between pigs is the main route of transmission for both PCV2 and PMWS. However, experimental inoculation of PCV2 to pigs does not give consistent results and severe clinical signs as encountered in the field are rarely obtained. It is thus acknowledged that additional conditions are required for the disease to be severe in growing pigs. These are not all known but co-infections are thought to act as triggers. The spread of such triggers/enhancers, which may or may not be infectious, could have played a role in PMWS dissemination via normal national and international trade, in some cases conferring an epidemic pattern to this spread. Most of the risk factors identified in surveys relate to poor biosecurity and inadequate hygiene/husbandry/herd management. The good correlation between viral burden in the tissues and disease severity emphasized the role of infection pressure. Genomic analysis showed great similarities between PCV2 isolates. However, although two main genotypes (genogroups) could be distinguished from the phylogenic trees, and changes with time, no clear relationship with strain virulence was apparent. Isolates detected in PMWS-positive pigs could also be detected in healthy pigs from healthy farms. A strong sow effect was observed in disease expression in the offspring. Colostrum composition and colostrum intake are supposed to be key components of disease expression. Medication is relatively inefficient as a control measure. Commercial PCV2 vaccines are now becoming available. However, losses as a result of PMWS and PCV2-related diseases are greatly reduced by applying appropriate hygiene and husbandry practices.

Vaccination of porcine circovirus type 2 (PCV2)-infected sows against porcine Parvovirus (PPV) and Erysipelas: effect on post-weaning multisystemic wasting syndrome (PMWS) and on PCV2 genome load in the offspring.

The effect of different Parvovirus+Erysipelas vaccination schemes in PCV2-infected sows on PMWS outcome in the offspring was investigated under experimental conditions. Six PCV2-free sows were first infected oro-nasally with PCV2 two months before insemination (D0; "Day 0") and then by the intra-uterine route at insemination (D62). On D21 and D42, vaccinated sows received either the two commercial monovalent vaccines, A1(PPV) and A2(Erysipelas), or the bivalent vaccine B (PPV+Erysipelas). In addition, three SPF sows (foster-sows) were synchronized for farrowing dates to enable them to foster piglets born to infected sows and removed at birth before colostrum intake. A significantly higher proportion of mummified fetuses was obtained from PCV2-infected non-vaccinated sows than from vaccinated sows. Acute myocarditis lesions were found in their piglets, together with a high PCV2 genome load. The latter was significantly higher than in those born to PCV2-infected vaccinated sows. Sentinel PCV2-negative piglets, born to SPF foster-sows, seroconverted at almost the same time as piglets without PCV2 passive immunity and born to infected sows. Sixteen of the 84 liveborn piglets born to infected sows and foster-sows were affected by a syndrome possibly related to PMWS, as judged by clinical signs and histological lesions. Most were born to PCV2-infected non-vaccinated sows and 12/16 did not receive PCV2 passive immunity. The probability of PCV2 infection and the number of PCV2 genome copies per gram of tissue were significantly increased in piglets that did not receive PCV2 passive immunity.

Pig anelloviruses are highly prevalent in swine herds in France.

A survey of anelloviruses in swine herds from Britanny, France, is reported. By using PCR targeted to the conserved untranslated region, prevalences of 93 and 73 % were found among 15 herds and 33 animals, respectively. The lung was the organ found to be positive most frequently among the five organs tested from 32 animals. The highest identity levels of our nucleotide sequences were found with pig isolates from Japan and with an isolate from Tupaia belangeri. Interestingly, when aligning all available swine isolates from France and Japan, at least two phylogenetic groups were identified, each one containing clones from France and Japan. Some animals carried clones from both groups, demonstrating intra-individual variability. Despite the putative harmlessness of anelloviruses, the potential inoculum carried by pigs must be further evaluated as a sanitary threat.

[Animal circoviruses and associated diseases]. / Circovirus et pathologies associées chez les animaux.

Animal circoviruses belong to the Circovirus genus of the Circoviridae family. Nowadays, only swine and birds were identified as circovirus hosts. Circoviruses have a single-stranded circular genome of approximately 2000 nucleotide long. DNA of these viruses possesses : (i) a nonanucleotide sequence essential for replication, flanked by inverted repeat sequences, a palindrome that has the potential to form a stem-loop structure and (ii) two major ORFs, located on the viral and complementary strands, which encode respectively the replication-associated protein (Rep) and the capsid protein (Cap). All the circoviruses described at the present time, except porcine circovirus of type 1, are associated with immunosuppressive or immunodepressive diseases. Histopathological lesions such as cytoplasmic inclusions of virus in histiocytic cells and T and B lymphocyte depletion in lymphoid organs, are commonly noticed. No medical prophylaxis of circovirus infections is currently available.