Bayesian estimation of the sensitivity and specificity of coprological and serological diagnostic tests for the detection of Ascaris suum infection on pig farms.

Coprological and serological diagnostic tests were compared to define the status of a pig farm with regard to Ascaris suum. On each of the 100 farms in France visited for the study, 10 blood samples were taken from pigs at the end of fattening (at least 22 weeks old) and 20 to 30 faecal samples were taken, depending on the category of animals present on the farm (10 sows, 10 piglets aged 10 to 12 weeks and 10 pigs at the end of fattening, aged at least 22 weeks). A SERASCA® ELISA test (Laboratory of Parasitology, Ghent University) was performed on each blood sample (cut-off 0.5) and a coprological analysis on each faecal sample. A Bayesian approach was used to estimate the sensitivity and specificity of the coprological and serological tests. A farm was considered positive if at least one A. suum egg was observed in the faecal samples. With regard to the serological test, various hypotheses were tested in order to define the number of seropositive animals required to consider a farm positive for A. suum. The coprological test has very good specificity in the search for A. suum, whether 20 or 30 samples are taken per farm. However, even with an increase in the number of samples, the sensitivity of this diagnostic approach is very low (less than 30%). On the other hand, the serological diagnostic method, which consists of taking blood samples from 10 animals at the end of fattening, has good sensitivity and seems better suited to defining the status of a farm with regard to A. suum, provided that a farm is considered seropositive only if two out of 10 samples are positive.

DESCRIPTIVE EPIDEMIOLOGY OF THE MAIN INTERNAL PARASITES ON ALTERNATIVE PIG FARMS IN FRANCE.

Alternative pig farms, which do not raise animals in closed buildings with slatted and/or concrete floors, have critical points that need particular attention. Internal parasitism is one, as the farming conditions in such structures are more favorable to the development and survival of parasites. The objectives of this study, carried out on 70 alternative farms in continental France, were to (i) estimate the frequency and level of infestation by the main internal parasites on these farms, and (ii) define their typology according to the level of parasitism. For this purpose, fecal samples were taken for coprological analysis from 10 sows, 10 pigs aged 10-12 wk, and 10 pigs at the end of the fattening period. Blood samples were also taken for serological analysis (targeting Ascaris suum and Toxoplasma gondii) from 10 sows and 10 pigs at the end of the fattening period. Of the 70 farms, only 5 had no helminth egg or coccidian oocyst. Coccidia oocysts were observed in 79% of the farms, while eggs of Oesophagostomum spp./Hyostrongylus rubidus, Ascaris suum, and Trichuris suis were found in 47%, 16%, and 36% of the farms, respectively. On each infested farm, an average of 56.8% of sows, 23.8% of grower pigs, and 38.9% of finisher pigs were parasitized. At least 1 Ascaris suum-seropositive finisher pig was found on 91% of the farms, and at least 1 Toxoplasma gondii-seropositive finisher pig or sow on 60% of the farms. Data on housing, animal management, and health management (particularly parasite control) were collected to characterize the typology of farms according to their level of parasitism. The variables defining these farm typologies differed according to the parasites. Access to the outdoors for breeding stock was a characteristic of the farms most heavily infested with helminths or T. gondii. Conversely, the farms with the lowest frequency of coccidia oocyst infestation were characterized by free-range farrowing facilities and also by the presence of slatted floors, mostly plastic in our study, rather than straw bedding in the farrowing rooms. The level of biosecurity concerning the storage of straw for pig bedding was another discriminating factor for parasitism level of helminths and T. gondii. Farms with the highest levels of helminth parasitism were more likely not to practice an all-in-all-out postweaning system and to deworm their grower/finisher pigs less frequently than farms with the lowest levels of helminth parasitism.

Coinfections and their molecular consequences in the porcine respiratory tract.

Understudied, coinfections are more frequent in pig farms than single infections. In pigs, the term "Porcine Respiratory Disease Complex" (PRDC) is often used to describe coinfections involving viruses such as swine Influenza A Virus (swIAV), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and Porcine CircoVirus type 2 (PCV2) as well as bacteria like Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae and Bordetella bronchiseptica. The clinical outcome of the various coinfection or superinfection situations is usually assessed in the studies while in most of cases there is no clear elucidation of the fine mechanisms shaping the complex interactions occurring between microorganisms. In this comprehensive review, we aimed at identifying the studies dealing with coinfections or superinfections in the pig respiratory tract and at presenting the interactions between pathogens and, when possible, the mechanisms controlling them. Coinfections and superinfections involving viruses and bacteria were considered while research articles including protozoan and fungi were excluded. We discuss the main limitations complicating the interpretation of coinfection/superinfection studies, and the high potential perspectives in this fascinating research field, which is expecting to gain more and more interest in the next years for the obvious benefit of animal health.

Assessment of Influenza D Virus in Domestic Pigs and Wild Boars in France: Apparent Limited Spread within Swine Populations Despite Serological Evidence of Breeding Sow Exposure.

In order to assess influenza D virus (IDV) infections in swine in France, reference reagents were produced in specific pathogen free pigs to ensure serological and virological analyses. Hemagglutination inhibition (HI) assays were carried out on 2090 domestic pig sera collected in 2012-2018 in 102 farms. Only 31 sera from breeding sows sampled in 2014-2015 in six farrow-to-finish herds with respiratory disorders contained IDV-specific antibodies. In two of them, within-herd percentage of positive samples (73.3% and 13.3%, respectively) and HI titers (20-160) suggested IDV infections, but virus persistence was not confirmed following new sampling in 2017. All growing pigs tested seronegative, whatever their age and the sampling year. Moreover, PB1-gene RT-qPCR performed on 452 nasal swabs taken in 2015-2018 on pigs with acute respiratory syndrome (137 farms) gave negative results. In Corse, a Mediterranean island where pigs are mainly bred free-range, 2.3% of sera (n = 177) sampled on adult pigs in 2013-2014 obtained low HI titers. Finally, 0.5% of sera from wild boars hunted in 2009-2016 (n = 644) tested positive with low HI titers. These results provide the first serological evidence that sows were exposed to IDV in France but with a limited spread within the swine population.

Longitudinal study describing time to Salmonella seroconversion in piglets on three farrow-to-finish farms.

BACKGROUND: Pigs are frequently colonised with Salmonella enterica, and this constitutes a major risk for human salmonellosis. The infection can be assessed by the serological response of pigs to S enterica. A longitudinal study was undertaken on-farm to correctly describe this serological response and investigate factors associated with age at Salmonella seroconversion. METHODS: Three pig farms and in each farm three successive batches were considered. Per batch, 40 piglets were selected at random from 10 sows (four piglets per sow). Blood was sampled from sows one week after farrowing and from piglets at weeks 1, 6, 10, 14, 18 and 22 and at the slaughterhouse. Salmonella antibodies were detected in serum using a commercial ELISA test. Factors related to farm characteristics, batch management system, porcine reproductive and respiratory syndrome infection, and sows' Salmonella serological status were recorded to assess their effect on age at seroconversion. RESULTS: At week 1 after farrowing, 96.5 per cent of the sows had antibodies against Salmonella. The serological results of piglets at weeks 1 and 6 only were positively correlated with those of the sows. The average age at Salmonella seroconversion was 137±2.2 days (confidence interval at 95 per cent). The first seroconversions occurred from weeks 10 to 14, but most of the pigs (54.6 per cent) were seropositive at the end of the fattening period, with variations between farms and batches (28.9-75.7 per cent). Herd/farm was significantly associated with age at seroconversion. CONCLUSION: This longitudinal study allowed the authors to follow precisely the evolution of Salmonella seroconversion from maternity to slaughterhouse and confirm the relationship between the seroconversion of sows and serology of their piglets. Moreover, factors related to farm practices and management as a whole are more influential than individual factors (at the pig level) on age at Salmonella seroconversion.

Virus persistence in pig herds led to successive reassortment events between swine and human influenza A viruses, resulting in the emergence of a novel triple-reassortant swine influenza virus.

This report describes the detection of a triple reassortant swine influenza A virus of H1avN2 subtype. It evolved from an avian-like swine H1avN1 that first acquired the N2 segment from a seasonal H3N2, then the M segment from a 2009 pandemic H1N1, in two reassortments estimated to have occurred 10 years apart. This study illustrates how recurrent influenza infections increase the co-infection risk and facilitate evolutionary jumps by successive gene exchanges. It recalls the importance of appropriate biosecurity measures inside holdings to limit virus persistence and interspecies transmissions, which both contribute to the emergence of new potentially zoonotic viruses.

Maternally-derived neutralizing antibodies reduce vaccine efficacy against porcine reproductive and respiratory syndrome virus infection.

Modified live virus (MLV) vaccines are commonly used to reduce the impact of porcine reproductive and respiratory syndrome (PRRS) but limited efficacy is achieved in field conditions. Here, we evaluated the impact of maternally-derived neutralizing antibodies (MDNAs) on vaccine efficacy after PRRS virus (PRRSV) challenge. Piglets with low (A-) or high (A+) MDNA levels derived from a commercial pig herd were moved to experimental facilities to be vaccinated (V+) or not (V-) with a PRRSV-1 MLV vaccine at 3 weeks of age (woa). Because of unexpectedly low vaccine detection in A-V+ piglets post-vaccination (pv), all V+ piglets received a second vaccination at 4 woa. Five weeks (W5) pv, piglets were inoculated with a PRRSV-1 field strain to evaluate vaccine protection, and were mingled 24 h later with non-inoculated piglets of similar immune status to assess viral transmission. Vaccine strain was detected at W2 pv in 69% and 6% of A-V+ and A+V+ piglets, and at W5 pv in 50% and 25% of A-V+ and A+V+ piglets, respectively. At W5 pv, 94% of A-V+ and 44% of A+V+ piglets seroconverted, with a significant IFNg response induction in the A-V+ group only. After challenge, compared to the V- inoculated group, viremia was 100-fold lower at 10 days post-infection in A-V+ whereas viremia was not significantly reduced in A+V+ piglets. A lower transmission rate was estimated for the A-V+ group: 0.15 [0.07-0.29] versus 0.44 [0.18-1.76] and 0.32 [0.14-0.68] for the A+V+ and V- groups, respectively. Investigations about the low vaccine strain detection after the first vaccination suggested a relationship between IFNa levels and vaccine strain detection in A-V+ piglets. We showed that MDNAs impair vaccine efficacy against PRRSV both in inoculated and contact piglets, probably by reducing vaccine replication. IFNa may also interfere with PRRSV vaccination. These new data could help improving vaccination protocols.

Assessment of pulmonary tissue responses in pigs challenged with PRRSV Lena strain shows better protection after immunization with field than vaccine strains.

The porcine reproductive and respiratory syndrome virus (PRRSV) is plaguing porcine production. Previously piglets were immunized with a PRRSV-1 commercial modified live virus vaccine (MLV1), a PRRSV-2 MLV (MLV2) or a Western European strain (Finistere: Fini) to assess and compare the protection brought by these strains upon challenge with virulent Lena strain. Lena viremia was reduced in all the immunized groups with a slightly higher level of protection following immunization with Fini. Using lung samples collected from the same experiment, tissue response to Lena challenge was assessed at the acute and chronic stages of infection. A pre-immunization with any one of the three PRRSV strains globally exacerbated microscopic lung lesions. Ten days post-challenge (DPC), MLV1 group score was higher than unimmunized group score and 42 DPC, MLV2 group score was higher than in unimmunized group. Lowest lung Lena viral loads were measured in Fini group. Using principal component analysis, we showed 10 DPC that the lesion score was positively correlated with chemokine receptors and negatively correlated with viral load. Forty-two DPC, variables for lesion score, IL6, IL8, and CCL20 transcripts were positively correlated together and negatively correlated with CCL28, CXCL6, and CXCR4 transcripts suggesting a role for the latter ones in the tissue recovery process. In conclusions, our study shows a significant impact of the three immunizations on pulmonary tissue with the best protection against Lena challenge conferred by Fini strain. Furthermore, it gives insight into the interactions between vaccine and Fini strains and the lung upon Lena challenge.

Intra-Species and Inter-Species Differences in Cytokine Production by Porcine Antigen-Presenting Cells Stimulated by Mycoplasma hyopneumoniae, M. hyorhinis, and M. flocculare.

Mycoplasma hyorhinis and M. flocculare are commonly co-isolated with M. hyopneumoniae (primary agent of swine enzootic pneumonia) in gross pneumonia-like lesions, but their involvement in the disease process remains unknown. T cells play an immuno-pathological role during mycoplasmal infections. Dendritic cells (DCs) are major antigen-presenting cells involved in T cell activation and differentiation. In this study, we investigated cytokine (IL-6, IL-8, IL-10, IL-12, and TNF-α) production by porcine bone-marrow-derived DCs (BM-DCs) stimulated by M. hyopneumoniae, M. hyorhinis, and/or M. flocculare. Results showed that cytokine production levels were relatively homogenous for all evaluated M. hyopneumoniae strains in contrast to M. hyorhinis and M. flocculare strains. The most noteworthy inter-species differences were the overall (i) lower IL-12 production capacity of M. hyopneumoniae, and (ii) higher TNF-α production capacity of M. flocculare. Co-stimulation of BM-DCs showed that M. hyorhinis dominated the IL-12 production independently of its association with M. hyopneumoniae or M. flocculare. In addition, a decreased BM-DC production of TNF-α was generally observed in the presence of mycoplasma associations. Lastly, M. flocculare association with M. hyopneumoniae increased BM-DC ability to secrete IL-10. A higher cytotoxicity level in BM-DCs stimulated by M. hyorhinis was also observed. Overall, this study demonstrated that the combination of M. hyorhinis or M. flocculare with M. hyopneumoniae may participate to the modulation of the immune response that might affect the final disease outcome.

Lessons learnt from a porcine epidemic diarrhea (PED) case in France in 2014: Descriptive epidemiology and control measures implemented.

An acute epidemic of porcine epidemic diarrhea (PED) has affected the USA since 2013 and spread all around the world. In France, the immune status of the pig population against PED virus (PEDV) was expected to be low due to the absence of circulation of the virus since the 80's and a compulsory notification of PED was set up in 2014. Here, we reported the first case of a PED outbreak in December 2014 in the North of France after a long absence of the disease, the monitoring of the excretion and the control measure implementation. The isolated strain in France in December 2014 was a PEDV "S-InDel" strain which was close to the "S-InDel" German PEDV strain isolated in May 2014. The individual shedding duration of PEDV in feces was estimated around 20 days for pigs of different ages. Biosecurity measures implemented allowed the limitation of PEDV spread to fattening and farrowing rooms without dissemination to the nursery block. Using strict biosecurity measures, direct shipment of infected fatteners to the slaughterhouse, strict decontamination protocols with a quarantine of 6 weeks for replacement gilts without voluntary contamination helped PEDV fade out within the herd and avoided the spread to other herds. PEDV presence in manure was investigated as well as the inactivation treatment of the virus present in the liquid manure. An increase to a pH 12 of liquid manure by liming led to the absence of PEDV detection by RT-PCR after seven days.

Colonization of Pigs Experimentally Infected with a Monophasic Variant of Salmonella Typhimurium.

The monophasic variant of Salmonella Typhimurium is highly prevalent in human and in pork. However, little is known about colonization dynamics and serology in pigs. We orally inoculated 24 seven-week-old piglets with 109 CFU/pig of a porcine strain of monophasic Salmonella Typhimurium in an experimental trial. Three groups of eight piglets were orally inoculated and monitored for 21, 49, or 84 days post-inoculation until necropsied. From 3 days post-inoculation to necropsy, individual feces were sampled twice weekly and blood once weekly. At necropsy, the tonsils, mesenteric lymph nodes, and the contents of the duodenum, jejunum, ileum, and cecum were collected from each pig. We determined the number of CFU/g in all the samples and measured also Salmonella antibodies in OD% in all blood samples. At different times during the trial, we tested by MLVA (Multilocus Variable Number Tandem Repeat Analysis) the genomic stability of the strain after passing through the intestinal tract. Salmonella was continuously excreted by pigs, ranging from 1.4 to 5.8 log10 CFU/g. At necropsy, Salmonella was present in all samples, but the tonsils were particularly infected. Salmonella antibodies were detected in five pigs 7 days post-inoculation. At 49 days post-inoculation, all the pigs were seropositive. We observed new MLVA types for 3.3% of the isolates tested over the trial. Our study allowed us to show the serovar's ability to persist in pigs after infection up to 84 days post-inoculation. We demonstrated that Salmonella seroconversion appeared earlier than in naturally infected pigs and that the strain's genome can evolve after passing through the digestive tract of pigs.

Estimating Parameters Related to the Lifespan of Passively Transferred and Vaccine-Induced Porcine Reproductive and Respiratory Syndrome Virus Type I Antibodies by Modeling Field Data.

The outputs of epidemiological models are strongly related to the structure of the model and input parameters. The latter are defined by fitting theoretical concepts to actual data derived from field or experimental studies. However, some parameters may remain difficult to estimate and are subject to uncertainty or sensitivity analyses to determine their variation range and their global impact on model outcomes. As such, the evaluation of immunity duration is often a puzzling issue requiring long-term follow-up data that are, most of time, not available. The present analysis aims at characterizing the kinetics of antibodies against Porcine Reproductive and Respiratory Syndrome virus (PRRSv) from longitudinal data sets. The first data set consisted in the serological follow-up of 22 vaccinated gilts during 21 weeks post-vaccination (PV). The second one gathered the maternally derived antibodies (MDAs) kinetics in piglets from three different farms up to 14 weeks of age. The peak of the PV serological response against PRRSv was reached 6.9 weeks PV on average with an average duration of antibodies persistence of 26.5 weeks. In the monitored cohort of piglets, the duration of passive immunity was found relatively short, with an average duration of 4.8 weeks. The level of PRRSv-MDAs was found correlated with the dams' antibody titer at birth, and the antibody persistence was strongly related to the initial MDAs titers in piglets. These results evidenced the importance of PRRSv vaccination schedule in sows, to optimize the delivery of antibodies to suckling piglets. These estimates of the duration of active and passive immunity could be further used as input parameters of epidemiological models to analyze their impact on the persistence of PRRSv within farms.

Individual and pen-based oral fluid sampling: A welfare-friendly sampling method for group-housed gestating sows.

The aims of this study were to assess the feasibility of individual and pen-based oral fluid sampling (OFS) in 35 pig herds with group-housed sows, compare these methods to blood sampling, and assess the factors influencing the success of sampling. Individual samples were collected from at least 30 sows per herd. Pen-based OFS was performed using devices placed in at least three pens for 45min. Information related to the farm, the sows, and their living conditions were collected. Factors significantly associated with the duration of sampling and the chewing behaviour of sows were identified by logistic regression. Individual OFS took 2min 42s on average; the type of floor, swab size, and operator were associated with a sampling time >2min. Pen-based OFS was obtained from 112 devices (62.2%). The type of floor, parity, pen-level activity, and type of feeding were associated with chewing behaviour. Pen activity was associated with the latency to interact with the device. The type of floor, gestation stage, parity, group size, and latency to interact with the device were associated with a chewing time >10min. After 15, 30 and 45min of pen-based OFS, 48%, 60% and 65% of the sows were lying down, respectively. The time spent after the beginning of sampling, genetic type, and time elapsed since the last meal were associated with 50% of the sows lying down at one time point. The mean time to blood sample the sows was 1min 16s and 2min 52s if the number of operators required was considered in the sampling time estimation. The genetic type, parity, and type of floor were significantly associated with a sampling time higher than 1min 30s. This study shows that individual OFS is easy to perform in group-housed sows by a single operator, even though straw-bedded animals take longer to sample than animals housed on slatted floors, and suggests some guidelines to optimise pen-based OFS success.

Efficacy of combined vaccination against Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus in dually infected pigs.

Porcine respiratory disease complex (PRDC) is one of the main causes of economic losses for swine producers. This complex is due to a combination of different pathogens and their interactions. Two major pathogens involved in PRDC are Mycoplasma hyopneumoniae (Mhp) and porcine reproductive and respiratory syndrome virus (PRRSV). The objectives of this study were (i) to develop an experimental model of dual Mhp/PRRSV infection in SPF pigs with European strains of Mhp and PRRSV and (ii) to assess and compare the effects of single Mhp, single PRRSV or combined Mhp/PRRSV vaccination against this dual infection. Pigs dually infected with Mhp and PRRSV showed a combination of symptoms characteristic of each pathogen but no significant exacerbation of pathogenicity. Thus, the co-infected pigs displayed coughing and pneumonia typical of Mhp infection in addition to PRRSV-related hyperthermia and decrease in average daily gain (ADG). Hyperthermia was reduced in PRRSV vaccinated animals (single or combined vaccination), whereas ADG was restored in Mhp/PRRSV vaccinated pigs only. Regarding respiratory symptoms and lung lesions, no vaccine decreased coughing. However, all vaccines reduced the pneumonia score but more so in animals receiving the Mhp vaccine, whether single or combined. This vaccine also decreased the Mhp load in the respiratory tract. In conclusion, combined vaccination against both Mhp and PRRSV efficiently pooled the efficacy of each single PRRSV and Mhp vaccination and could be an interesting tool to control PRDC in European swine production.

Complete genome sequence of a porcine epidemic diarrhea s gene indel strain isolated in france in december 2014.

We report the first and only case of a porcine epidemic diarrhea (PED) outbreak occurring in December 2014 in northern France, and we show using the full-length genome sequence of the French PED virus (PEDV) isolate that it was a PEDV indel strain close to German PEDV strains recently isolated.

The use of Bayesian methods for evaluating the performance of a virus-like particles-based ELISA for serology of hepatitis E virus infection in swine.

In the absence of commercial kits for serological studies specifically for hepatitis E virus (HEV) infection of swine, the capsid protein of a swine genotype 3 HEV was expressed using a recombinant baculovirus. This antigen was used in an enzyme-linked immunosorbent assay (ELISA) for detection of anti-HEV antibodies. Estimation of sensitivity and specificity was carried out in comparison with a commercial serological assay using sera from pigs infected experimentally with HEV genotype 3, negative sera from SPF pigs and swine sera collected at slaughterhouses. Since a "gold standard" is not available, a latent-class Bayesian approach for correlated tests was used to estimate the sensitivity and specificity of both tests. External field and experimental data were used to determine the parameters of Beta prior distributions. The estimated mean sensitivity of the commercial test was 0.47 with a 95% credibility interval of 0.39-0.55, whereas the estimated mean sensitivity of the genotype 3-based assay was 0.92 [0.81-0.99]. The estimated specificities were 0.98 [0.93-0.99] and 0.98 [0.95-0.99] for the genotype 3-based test and commercial test, respectively. In conclusion, genotype 3-antigen derived from swine HEV is a better candidate for assessing hepatitis E serology in swine.

Experimental infection of SPF pigs with Actinobacillus pleuropneumoniae serotype 9 alone or in association with Mycoplasma hyopneumoniae.

The purpose of this study was to compare in SPF pigs, the pathogenicity of an Actinobacillus pleuropneumoniae serotype 9 strain 21 (isolated from the palatine tonsils of a healthy gilt on a French nucleus pig farm, with no clinical signs or lung lesions but a highly positive reaction to A. pleuropneumoniae serotype 9 antibodies) with a pathogenic A. pleuropneumoniae strain 4915 serotype 9 (isolated in France from an outbreak of porcine pleuropneumonia). The pathogenicity of one Mycoplasma hyopneumoniae strain alone or associated with A. pleuropneumoniae strain 21 was also compared. Eight groups of 7 pigs were infected (at 6 or 10 weeks of age) and a control group was kept non-infected. Results showed that sensitivity to A. pleuropneumoniae was related to the age of the pig (6 weeks vs 10 weeks) whatever the strain. Surviving pigs infected at 6 weeks of age developed severe clinical signs, lung lesions typical of A. pleuropneumoniae and they seroconverted. In contrast, symptoms and lung lesions were almost non-existent in pigs infected with strain 21 at 10 weeks of age, but a seroconversion was observed with very high ELISA titres. These results were in accordance with those observed in the nucleus pig farm. Infection with M. hyopneumoniae alone induced typical mycoplasmal symptoms, pneumonia and seroconversion. Symptoms and lung lesions were the most noticeable in pigs infected with M. hyopneumoniae at 6 weeks of age and with A. pleuropneumoniae 4 weeks later. Our results show that the presence of A. pleuropneumoniae serotype 9 in a pig herd may be clinically unnoticed and that M. hyopneumoniae may potentiate A. pleuropneumoniae infection.

Risk factors for Salmonella seroconversion of fattening pigs in farrow-to-finish herds.

We did a prospective observational 9-month long study to quantify risk factors of managerial and hygiene practices, and pig-health status for Salmonella seroconversion of fattening pigs reared in subclinically infected French farrow-to-finish farms. During the fattening phase, 2,649 pigs belonging to the same batch of contemporary pigs, from 89 conventional farrow-to-finish farms were individually followed and regularly blood sampled on a monthly basis. Farm recruitment was based on the farmer's willingness to cooperate. Pig status was assessed using an indirect ELISA test. Evolution of the serological status was studied by means of survival analysis. A Cox proportional-hazards model, taking into account the clustering of animals at the farm level, was used to examine the effects of explanatory variables on the time to Salmonella seroconversion of pigs. Applying group level antibiotic treatment to the pigs during the fattening period (Hazard Ratio (HR) = 2.4; 95% CI: 1.7, 3.4) was identified as a risk factor for Salmonella seroconversion, as the presence of residual Salmonella contamination in the fattening pen before placing the pigs into the pens (HR = 1.9; 95% CI: 1.2, 2.9). Porcine reproductive and respiratory syndrome virus (PRRSV) seropositivity during the fattening period also indicated an increased hazard for seroconversion (HR = 1.6; 95% CI: 1.1, 2.5). The batch size was identified as a risk factor for Salmonella seroconversion: the higher the number of pigs was in the fattening room followed, the higher was the risk (HR(+10 pigs) = 1.05 for a 10-pig increment; 95% CI: 1.03, 1.06). The biosecurity measures of wearing specific clothes before entering the facilities (HR = 0.5; 95% CI: 0.3, 0.9) and enclosing the pig farm facilities were protective (HR = 0.4; 95% CI: 0.2, 0.8).

Listeria monocytogenes contamination of finishing pigs: an exploratory epidemiological survey in France.

Listeria monocytogenes is a foodborne pathogen of major concern for public health in industrialised countries. Since L. monocytogenes carriage by pigs at the herd level could be a primary source for carcass contamination, control measures should be designed to reduce the L. monocytogenes load at the pre-harvest stage. For this purpose, an exploratory analytical survey was carried out in 2000-2001 in 93 French farrow-to-finish pig farms concerning L. monocytogenes contamination in pigs before they left for the slaughterhouse. On each farm, the L. monocytogenes status of a batch of contemporary fattening pigs housed in the same room was assessed on faecal material samples taken by means of gauze swabs wiped on the perianal region of the pigs. Fourteen percent of the batches studied had at least one contaminated sample and were therefore classified as L. monocytogenes contaminated batches. Two logistic regression models were used to assess the association between managerial and hygiene practices and the risk of L. monocytogenes contamination of the batch at the end of the finishing period on the whole data set (n = 93) and in the wet feeding farms only (n = 57). Wet feeding during the fattening period was identified as a risk factor for L. monocytogenes contamination. Risk factors related to the introduction of L. monocytogenes in pig facilities were identified for both the general and wet feeding farm data sets. Poor care paid to hygiene on the farms was found to increase the risk of being infected (boots cleaning, change room presence). When the duration of the empty period prior to the introduction of growing pigs was less than one day in the fattening section, the risk of L. monocytogenes contamination was significantly increased. For wet feeding farms, a distribution pipeline cleaning procedure including disinfection was found to be associated with a higher risk of contamination than no cleaning or a procedure consisting of rinsing with water only.