Françoise Pol

Preventive vaccination contributes to control classical swine fever in wild boar (Sus scrofa sp.)

Over the last 20 years, oral vaccination implementing a live attenuated vaccine has been experimented in Europe in order to control classical swine fever (CSF) in Wild Boar (Sus scrofa sp.). This has generally led to an enhanced seroprevalence and a decreased viroprevalence at the scale of the whole vaccinated populations, but no quantitative analysis has demonstrated the protective effect of preventive vaccination or intensive baiting. In the present paper we conducted a retrospective analysis at the scale of the municipality, taking into account the local dynamics and possible covariates of infection to test the effect of preventive vaccination and of the baiting effort. To be efficient, vaccination was expected to increase seroprevalence above the level considered as suitable for preventing disease invasion (40-60%) independently of infection, to protect free areas from disease invasion or contribute to control subsequent disease intensity and duration. We also hypothesized that a better baiting effort would be correlated with an improvement of immunisation and disease control. In uninfected municipalities, seroprevalence increased up to 40% after 1 year, i.e., three vaccination campaigns. We observed a significant protective effect of preventive vaccination, especially within municipalities that had been vaccinated at least 1 year before disease emergence and where virus detection did not last more than one quarter. On the other hand, we did not detect a significant effect of the baiting effort on local seroprevalence or disease dynamics, suggesting that the baiting system could be improved. We discuss these results regarding the improvement of management measures and further research perspective.

New Insights on the Management of Wildlife Diseases Using Multi-State Recapture Models: The Case of Classical Swine Fever in Wild Boar

Background The understanding of host-parasite systems in wildlife is of increasing interest in relation to the risk of emerging diseases in livestock and humans. In this respect, many efforts have been dedicated to controlling classical swine fever (CSF) in the European Wild Boar. But CSF eradication has not always been achieved even though vaccination has been implemented at a large-scale. Piglets have been assumed to be the main cause of CSF persistence in the wild since they appeared to be more often infected and less often immune than older animals. However, this assumption emerged from laboratory trials or cross-sectional surveys based on the hunting bags. Methodology/Principal Findings In the present paper we conducted a capture-mark-recapture study in free-ranging wild boar piglets that experienced both CSF infection and vaccination under natural conditions. We used multi-state capture recapture models to estimate the immunization and infection rates, and their variations according to the periods with or without vaccination. According to the model prediction, 80% of the infected piglets did not survive more than two weeks, while the other 20% quickly recovered. The probability of becoming immune did not increase significantly during the summer vaccination sessions, and the proportion of immune piglets was not higher after the autumn vaccination. Conclusions/Significance Given the high lethality of CSF in piglets highlighted in our study, we consider unlikely that piglets could maintain the chain of CSF virus transmission. Our study also revealed the low efficacy of vaccination in piglets in summer and autumn, possibly due to the low palatability of baits to that age class, but also to the competition between baits and alternative food sources. Based on this new information, we discuss the prospects for the improvement of CSF control and the interest of the capture-recapture approach for improving the understanding of wildlife diseases.

Validation of commercial real-time RT-PCR kits for detection of influenza A viruses in porcine samples and differentiation of pandemic (H1N1) 2009 virus in pigs.

Swine influenza, apart from its importance in animal health, may also be of public health significance. Although the first human infections with the multi-reassortant H1N1 virus (pH1N1/09) responsible for the 2009 pandemic were not related to pig exposure, this virus was shown to be related genetically to swine influenza viruses (SIV) and easily transmissible to pigs. In addition to direct animal health concerns, transmission and possible adaptation of the pH1N1/09 virus in pigs may have serious consequences on the risk of human infection by increasing the reservoir of this virus and the risk of possible emergence of new reassortant viruses with increased virulence for pigs and/or humans. Sensitive tools to monitor and detect rapidly such an infection are therefore mandatory. In this study, five commercial real-time RT-PCR assays developed by manufacturers LSI and Adiagène were assessed and validated, (i) for rapid detection of influenza A viruses, including pH1N1/09, in pig and (ii) for the differentiation of pH1N1/09 in that species. Two kits target the influenza A virus M gene, two others amplify the pH1N1/09 virus H1 gene and one kit targets the pH1N1/09 virus N1 gene. All five kits are ready-to-use, one-step duplex RT-PCR and contain an internal positive control (IPC), appropriate for porcine biological samples, for assessing RNA extraction efficiency and the presence of PCR inhibitors. They have been used successfully by veterinary laboratories and shown to be powerful tools for the diagnosis and epidemiological surveillance of influenza virus infections in pigs.

Risk factors associated with leg disorders of gestating sows in different group-housing systems: A cross-sectional study in 108 farrow-to-finish farms in France

Group-housing, rather than individual-housing systems, is mandatory for gestating sows in the European Union (2008/120/EEC). However, leg problems occur more frequently in group-housing than in individual-housing systems and are a welfare and health concern. A cross-sectional study involving 108 farms in western France was carried out to see whether the type of the 4 main group-housing systems (i.e. large groups with electronic feeder station in stable or in dynamic groups, small groups in walk-in lock-in stalls or partial feeding stalls), and other husbandry practices, were associated with leg disorders. In each farm, the sows were examined visually for claw lesions, scored for lameness and their breeding characteristics were recorded. Lameness was positively correlated with heel lesions and dewclaw lesions. A concrete slatted floor, as compared to straw, was a major risk factor (unadjusted relative risk (RR)=9.9; 95% confidence interval (95% CI): 4.4-34.5). Walk-in lock-in stalls were found to be the most protective system. A logistic regression model was used to identify those factors which significantly increased the risk of leg problems. These factors were: housing in large groups (RR=1.5; 95% CI: 1.1-2.4), dirty floors (RR=1.6; 95% CI: 1.0-2.9), high level of ammonia (RR=1.5; 95% CI: 1.1-2.1), severely restricted feeding particularly during the last stage of pregnancy (RR=1.5; 95% CI: 1.0-2.1) and a high number of sows per stockman (RR=1.5; 95% CI: 1.0-2.4).

Validation of a commercial real-time PCR kit for specific and sensitive detection of Pseudorabies

Pseudorabies virus is the causative agent of Aujeszkys disease, one of the OIE listed diseases that mainly affects swine, but also can affect other animal species, and which can lead to heavy economic losses in pig industry. This study was designed to evaluate the performance of the ADIAVET(®) PRV REALTIME kit, a new commercial real time PCR kit for Pseudorabies virus genome detection developed by the French manufacturer Adiagène. It can be used on pig biological samples such as nasal swab supernatant, tonsil, brain or lung samples, or on samples from other susceptible animals, such as domestic carnivores. This ready-to-use duplex PCR assay contains an external positive control, appropriate for assessing DNA extraction efficiency and the presence of PCR inhibitors. The analytical specificity and sensitivity, intra- and inter-assay repeatability and diagnostic characteristics of the kit were determined and compared with virus isolation, which is the gold standard. Based on these results, the ADIAVET(®) PRV REALTIME kit received full validation for diagnostic purposes.

Oral fluid versus blood sampling in group-housed sows and finishing pigs: Feasibility and performance of antibody detection for porcine reproductive and respiratory syndrome virus (PRRSV)

The feasibility of using individual and pen-based oral fluid samples to detect PRRSV antibodies in growing-finishing pigs and group-housed sows was investigated. The diagnostic performances of a commercial oral fluid ELISA (OF-ELISA) and a serum ELISA (SER-ELISA) performed on individual or pooled samples from 5 or 10 pigs and sows was evaluated. The performance of the OF-ELISA was also assessed for pen-based oral fluids. Eight hundred and thirty-four pigs and 1598 sows from 42 PRRSV-infected and 3 PRRSV-negative herds were oral fluid sampled and bled. PRRSV antibodies were detected by an OF-ELISA performed at individual, pool (5 or 10 samples) and pen levels. Serum samples were tested by a SER-ELISA at individual and pool levels. The sensitivity and specificity of ELISAs for individual samples were assessed by Bayesian analysis. The relative diagnostic performance for the pools was calculated by taking individual samples as the gold standard. SER-ELISA and individual OF-ELISA results were used as references for estimating OF-ELISA performance for pen-based samples. Individual oral fluid collection was feasible in all kinds of pigs, whereas pen-based samples were unsuccessful in 40% of the group-housed sow pens. High levels of sensitivity comparable to those of the SER-ELISA were found for the OF-ELISA when performed on individual, 5-sample pool or pen-based samples from pigs or sows. The OF-ELISA lacked specificity for individual samples from sows. Pooling 5 individual oral fluid samples or using pen-based samples increased test specificity.

HERPÈSVIROSE CHEZ LE PORC: LA MALADIE D'AUJESZKY

Aujeszkys disease, due to Suid herpesvirus 1, is a disease of wild and domestic pigs, which can occasionally infect other mammal species, such as cattle and domestic carnivores. Eradicated or in the process of being eradicated in domestic pig herds in most countries of the European Union and in North America, the disease remains endemic in wild boar populations, with a prevalence varying according to population densities. In domestic pigs, symptoms vary depending on the age of the animals, ranging from severe nervous disorders in piglets to respiratory and reproductive disorders in adults. In other species, the disease causes a fatal meningo-encephalitis. Control programmes usually combine vaccination with marker vaccines and screening with companion diagnostic kits. In countries free from Aujeszkys disease, serological surveillance is supplemented by active surveillance.

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.