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.

Bacterial pathogens associated with lung lesions in slaughter pigs from 125 herds

Relationships between macroscopic lesions and Polymerase Chain Reaction (PCR) detection of Mycoplasma hyopneumoniae (Mhp), Pasteurella multocida (Pm), Actinobacillus pleuropneumoniae (App), Haemophilus parasuis (Hps) and Streptococcus suis (Ssuis) of the lungs of 3731 slaughter pigs from 125 herds were assessed in France. Pneumonia and pleuritis were the most frequent lesions (69.3% and 15% of the lungs, respectively). Mhp, Pm, App, Ssuis and Hps were detected in 69.3%, 36.9%, 20.7%, 6.4% and 0.99% of the lungs, respectively. Mhp and Pm were associated with pneumonia at both the pig and herd levels. Pleuritis was not associated with any pathogen at the pig level, but was associated with a high percentage of pigs PCR-positive for App at the herd level. Measures focused on control of Mhp, Pm and App should significantly reduce the occurrence of both pneumonia and pleuritis.

Longitudinal study of respiratory infection patterns of breeding sows in five farrow-to-finish herds

A longitudinal study was carried out in five French farrow-to-finish herds differently affected by respiratory diseases to describe the carrying and infection patterns of batches of sows to various respiratory pathogens during gestation and lactation. An entire batch of sows was followed during two successive reproduction cycles. Nasal, tonsillar and oro-pharyngeal swabs and blood samples were taken from each sow 9 and 4 weeks before farrowing and 1 and 4 weeks after farrowing. Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Pasteurella multocida, Haemophilus parasuis and Streptococcus suis were detected from swab samples using PCR assays. Blood samples were tested for antibodies against M. hyopneumoniae, A. pleuropneumoniae serotypes 1-9-11 and 2, Porcine Circovirus type-2 (PCV-2) and Porcine Reproductive and Respiratory Syndrome virus (PRRSV) by ELISA tests. Antibodies against H₁N₁, H₁N₂ and H₃N₂ Swine Influenza Viruses (SIV) of European lineages were tested by hemagglutination inhibition assay. The results indicated that S. suis is widespread among sows (67.1% of PCR-positive sows). A. pleuropneumoniae, P. multocida, and H. parasuis were detected by PCR in 30.9%, 24.6% and 23.4% of the sows, respectively. Antibodies against M. hyopneumoniae were recovered from more than 55% of the sows in all herds whereas the micro-organism was detected in 2.4% of the sows. Although PCV-2 and SIV infections were highly prevalent, the PRRSV infection patterns ranged from no infection in farms mildly affected by respiratory diseases to active circulation in more severely affected herds. The sow population thus constitutes a reservoir for a continuous circulation of respiratory pathogens and needs to be properly considered in control strategies.

Estimation of the sensitivity of four sampling methods for Mycoplasma hyopneumoniae detection in live pigs using a Bayesian approach

Four sampling techniques for Mycoplasma hyopneumoniae detection, namely nasal swabbing, oral-pharyngeal brushing, tracheo-bronchial swabbing and tracheo-bronchial washing, were compared in naturally infected live pigs. In addition, a quantitative real-time PCR assay for M. hyopneumoniae quantification was validated with the same samples. 60 finishing pigs were randomly selected from a batch of contemporary pigs on a farm chronically affected by respiratory disorders. Each pig was submitted to nasal swabbing, oral-pharyngeal brushing, tracheo-bronchial swabbing and tracheo-bronchial washing. Nested-PCR and real-time PCR assays were performed on all samples. A Bayesian approach was used to analyze the nested-PCR results of the four sampling methods (i.e. positive or negative) to estimate the sensitivity and specificity of each method. M. hyopneumoniae was detected by nested-PCR in at least one sample from 70% of the pigs. The most sensitive sampling methods for detecting M. hyopneumoniae in live naturally infected pigs were tracheo-bronchial swabbing and tracheo-bronchial washing, as compared to oral-pharyngeal brushing and nasal swabbing. Swabbing the nasal cavities appeared to be the least sensitive method. Significantly higher amounts of M. hyopneumoniae DNA were found at the sites of tracheo-bronchial sampling than in the nasal cavities or at the oral-pharyngeal site (p<0.001). There was no difference between the tracheo-bronchial washing and the tracheo-bronchial swabbing results (p>0.05). Our study indicated that tracheo-bronchial swabbing associated with real-time PCR could be an accurate diagnostic tool for assessing infection dynamics in pig herds.

Development of a quantitative Real-Time TaqMan PCR assay for determination of the minimal dose of Mycoplasma hyopneumoniae strain 116 required to induce pneumonia in SPF pigs

AIMS

A triplex real-time PCR assay to quantify Mycoplasma hyopneumoniae in specimens from live and dead pigs was developed and validated. The minimal dose of Myc. hyopneumoniae required to induce pneumonia in specific pathogen-free pigs was determined.

METHODS AND RESULTS

This TaqMan test simultaneously detected three genes encoding the proteins P46, P97 and P102. All Myc. hyopneumoniae strains analysed were detected, including strains isolated in three countries (France, England and Switzerland) and from several pig farms (n = 33), and the test was specific. The estimated detection thresholds were 1.3 genome equivalents (microl(-1)) for the targets defined in p97 and p102 genes and 13 genome equivalents (microl(-1)) for the segment defined in the p46 gene. This test was used to quantify Myc. hyopneumoniae in specimens sampled from experimentally infected pigs. In live pigs, c. 10(7), 10(8) and 10(10) genome equivalents (ml(-1)) of Myc. hyopneumoniae were detected in the nasal cavities, tonsils and trachea samples, respectively. In dead pigs, 10(8)-10(10) genome equivalents (ml(-1)) of Myc. hyopneumoniae were detected in the lung tissue with pneumonia. The estimated minimal dose of Myc. hyopneumoniae required to induce pneumonia was 10(5) colour-changing units (CCU) per pig (corresponding to 10(8) mycoplasmas).

CONCLUSION

The triplex RT-PCR test was validated and can be used for testing samples taken on the pig farms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This test should be a very useful tool in pig herds to control enzootic pneumonia or healthy carrier pigs and to study the dynamics of Myc. hyopneumoniae infections.

Isolation of Mycoplasma hyopneumoniae from different sampling sites in experimentally infected and contact SPF piglets

The purpose of this study was to determine the optimal route of infection and the optimal sampling sites for the recovery of M. hyopneumoniae, the etiological agent of enzootic porcine pneumonia. Virulence of two strains, BQ 14 and 116, isolated in France in 1975 and 2003, respectively, was also compared. Groups of specific pathogen free piglets were experimentally infected by the intratracheal or intranasal route. One non-inoculated pig was placed in each group of infected pigs to study direct transmission. Two groups were kept uninfected. Coughing was recorded daily. Blood samples, nasal, tonsillar and tracheal swabs and tracheobronchiolar washings were collected weekly. Pigs were killed 27-37 days post-infection. Lung lesions were scored and swabs were collected from nasal cavities, tonsils, trachea, lung, liver and spleen. All the samples, collected from live and dead pigs, were cultured for M. hyopneumoniae recovery. Results showed that both experimentally infected pigs and contact pigs developed enzootic pneumonia, whatever the route of infection and the strain tested. Direct contact transmission occurred quickly. No difference between the two routes of infection or between the two strains tested was evidenced, but high individual variations were observed between pigs. Tracheal swabs and tracheobronchiolar washings were the most effective samples to detect M. hyopneumoniae compared to nasal or tonsillar swabs. Our results also suggested that tracheobronchiolar washings could have an influence on the lesion extent observed at necropsy. M. hyopneumoniae could be re-isolated from liver and spleen of experimentally infected pigs and contact pigs.

Persistence of Mycoplasma hyopneumoniae in experimentally infected pigs after marbofloxacin treatment and detection of mutations in the parC gene

The ability of Mycoplasma hyopneumoniae to persist despite fluoroquinolone treatments was investigated with pigs. Groups of specific-pathogen-free pigs were experimentally infected with M. hyopneumoniae strain 116 and treated with marbofloxacin at the therapeutic dose (TD) or half of the therapeutic dose (TD/2) for 3 days. Results showed that, despite tissue penetration of marbofloxacin, particularly in the trachea and the tracheal secretions, the treatments did not have any influence on M. hyopneumoniae recovery from tracheal swabs. Mycoplasmas were also isolated from inner organs and tissues such as liver, spleen, kidneys, and bronchial lymph nodes. Recontamination of pigs via environment could not explain mycoplasma persistence after medication, as decontamination of pigs and allocation to a new disinfected environment did not have any significant effect on the phenomenon. A significant decrease in the susceptibility level to marbofloxacin of 12 mycoplasma clones reisolated after the treatments (TD/2 and TD) was observed. Two point mutations were found in the ParC quinolone resistance-determining region (QRDR) of DNA topoisomerase IV (Ser80-->Phe and Asp84-->Asn), and one point mutation was observed just behind the QRDR of ParC (Ala116-->Glu). This is the first time that mutations in a gene coding for topoisomerase IV have been described for M. hyopneumoniae after in vivo marbofloxacin treatments in experimentally infected pigs. However, development of resistance is not sufficient to explain M. hyopneumoniae persistence in vivo since (i) marbofloxacin concentrations were above the marbofloxacin MIC of the wild-type strain and (ii) mycoplasmas reisolated after a single injection of marbofloxacin did not display an increased marbofloxacin MIC.

Multiplex PCR assay for detection of Streptococcus suis species and serotypes 2 and 1/2 in tonsils of live and dead pigs

A PCR assay was developed for the detection of Streptococcus suis serotypes 2 and 1/2. This multiplex PCR is based on the amplification of the gene coding for 16S rRNA of S. suis and on the amplification of the cps2J gene coding for the capsule of S. suis serotypes 2 and 1/2. An internal control was constructed and added in this test to monitor the efficiency of amplification in each reaction. To evaluate the specificity of the test, 31 strains of other bacterial species related to S. suis or isolated from pigs and 42 strains of S. suis serotypes 1 and 3 to 34 were analyzed. The detection threshold of the test was 28 S. suis CFU/ml. The specificity and the sensitivity of the multiplex PCR test and the presence of an internal control allowed the analysis of biological samples without a culture step. The PCR assay was then applied to the detection of 14 S. suis serotype 1/2 strains, 88 S. suis serotype 2 strains isolated from pigs, and 25 S. suis serotype 2 strains isolated from humans. This test was also applied to analyze tonsil samples of pigs experimentally infected and carrier pigs without any symptoms.

Use of recombinant ApxIV in serodiagnosis of Actinobacillus pleuropneumoniae infections, development and prevalidation of the ApxIV ELISA

Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia, which causes worldwide severe losses in pig farming. The virulence of the 15 serotypes of A. pleuropneumoniae is mainly determined by the three major RTX toxins ApxI, ApxII and ApxIII, which are secreted by the different serotypes in various combinations. A fourth RTX toxin, ApxIV, is produced by all 15 serotypes only during infection of pigs, but not under in vitro conditions. Pigs infected with A. pleuropneumoniae show specific antibodies directed against ApxIV. In contrast, antibodies against the other three toxins ApxI, ApxII and ApxIII are also found in pigs free of A. pleuropneumoniae. The antibodies to the three latter might result from other, less pathogenic Actinobacillus species such as A. rossii and A. suis. We used a recombinant protein based on the N'-terminal part of ApxIV to serologically detect A. pleuropneumoniae infections in pigs by immunoblot analysis. The analysis of sera of experimentally infected pigs revealed that ApxIV-immunoblots detected A. pleuropneumoniae infections in the second to third week post infection. We developed an indirect ELISA based on the purified recombinant N'-terminal moiety of ApxIV. The analysis of sera from pigs that were experimentally or naturally infected by A. pleuropneumoniae, and of sera of pigs that were free of A. pleuropneumoniae, revealed that the ELISA had a specificity of 100% and a sensitivity of 93.8%. The pre-validation study of the ApxIV-ELISA revealed that the latter was able to detect A. pleuropneumoniae-positive herds, even when clinical and pathological signs of porcine pleuropneumonia were not evident. Pigs vaccinated with a subunit vaccine Porcilis App were serologically negative in the ApxIV-ELISA.

An attempt at measuring health in nucleus and multiplier pig farms

A pilot epidemiological inquiry was undertaken in France in a group of 205 nucleus and multiplier pig farms. The aim was to find out a method for a quantitative evaluation of the health level in farms selling young breeders. An exhaustive protocol was prepared for data collection. The sources of information were clinical inspections on the farms, meat inspection data at slaughter and laboratory investigations. Data processing issued in the selection of a profile made of 14 prevailing health indicators. These were then associated so as to set up a health index with an overall score. In a second phase, the relevance of the method with respect to disease transmission was assessed. The principle was a contact challenge within totally controlled facilities between SPF pigs hysterectomy-derived and gilts taken from farms with different health scores as previously checked. The contact lasted for 28 days. Eleven farms were chosen and in every one of them 7 gilts were sampled and 10 SPF pigs were assigned to each of these farms. All the pigs were submitted to a detailed observation. At the end of it the pigs were euthanized at the laboratory and checked to find out any lesions and infectious agents. A wide range of symptoms appeared among the SPF pigs. Mortality rate was 14.6%. Pneumonia affected 23.7% of them. A relationship was found between the germ transfer and the severity of the troubles. The degree of illness in SPF pigs was clearly related to the score obtained previously in the corresponding farms. Consequently, the method was considered as valid with respect to health evaluation.

Non-pathogenic Actinobacillus isolates antigenically and biochemically similar to Actinobacillus pleuropneumoniae: a novel species?

Two unusual Actinobacillus isolates were recovered from pigs with no clinical signs, no lesions and no history of swine pleuropneumonia. Two representative strains (9953L55 and 0347) analyzed in this study were initially biochemically and antigenically identified as A. pleuropneumoniae serotypes 1 and 9, respectively, by traditional identification methods. Both strains presented, however, negative results with three A. pleuropneumoniae-specific PCR tests and revealed in particular the absence of the apxIV toxin genes. However, both strains produced and secreted ApxII toxin although they only harbored the toxin genes apxIICA, which is an uncommon feature for any of the known A. pleuropneumoniae serotypes. Upon experimental inoculation of pigs, these strains proved to be totally non-pathogenic. Animals infected with one of the strains produced antibodies that cross-react with A. pleuropneumoniae serotypes 1-9-11-specific LC-LPS ELISA. Phylogenetic analysis based on 16S rRNA gene sequence analysis revealed that these strains form a separate phylogenetic group that is distinct from other Actinobacillus species and is particularly different from A. pleuropneumoniae.

A reverse transcription-PCR assay to detect viable Mycoplasma synoviae in poultry environmental samples

In order to study horizontal transmission of Mycoplasma synoviae an avian pathogen, a reverse transcription-polymerase chain reaction (RT-PCR) assay was developed to detect viable Mycoplasma in environment. The test was based on the RT-PCR of the 16S ribosomal RNA (rRNA) of Mycoplasma genus. Results showed that Mycoplasma 16S rRNA was stable up to 23 h after cell death. Therefore, the test allowed detection of viable or very recently (less than 23 h) dead mycoplasmas. M. synoviae survival in artificially contaminated water, food and soil and in the environment of M. synoviae experimentally infected turkeys was estimated by culture and RT-PCR. The RT-PCR method was then applied in a naturally infected laying hen farm showing problems of recurrent mycoplasmosis in the hens. Results confirmed the usefulness of RT-PCR in checking the efficiency of biosecurity measures and in improving cleaning and disinfection protocols.

Fluoroquinolone resistance in Mycoplasma gallisepticum: DNA gyrase as primary target of enrofloxacin and impact of mutations in topoisomerases on resistance level

Resistant mutants of Mycoplasma gallisepticum were selected in vitro by passaging strains 10 times in increasing concentrations of enrofloxacin. The regions of gyrA/gyrB and parC/parE, encoding the quinolone resistance-determining regions (QRDRs) of DNA gyrase and DNA topoisomerase IV, respectively, of the mutants obtained during different passages were sequenced. Several mutations were found in the four fluoroquinolone targets. Substitution of Ser-83-->Arg in GyrA and Ser-80-->Leu or Trp in ParC QRDRs seem to have the greatest impact on resistance to fluoroquinolones. The results obtained also suggest that the preferential target of enrofloxacin in M. gallisepticum is DNA gyrase.

In vitro development of resistance to enrofloxacin, erythromycin, tylosin, tiamulin and oxytetracycline in Mycoplasma gallisepticum, Mycoplasma iowae and Mycoplasma synoviae

The in vitro emergence of resistance to enrofloxacin, erythromycin, tylosin, tiamulin, and oxytetracycline in three avian Mycoplasma species, Mycoplasma gallisepticum, Mycoplasma synoviae and Mycoplasma iowae was studied. Mutants were selected stepwise and their MICs were determined after 10 passages in subinhibitory concentrations of antibiotic. High-level resistance to erythromycin and tylosin developed within 2-6 passages in the three Mycoplasma species. Resistance to enrofloxacin developed more gradually. No resistance to tiamulin or oxytetracycline could be evidenced in M. gallisepticum or M. synoviae after 10 passages whereas, resistant mutants were obtained with M. iowae. Cross-sensitivity tests performed on mutants demonstrated that mycoplasmas made resistant to tylosin were also resistant to erythromycin, whereas mutants made resistant to erythromycin were not always resistant to tylosin. Some M. iowae tiamulin-resistant mutants were also resistant to both macrolide antibiotics. Enrofloxacin and oxytetracycline did not induce any cross-resistance to the other antibiotics tested. These results show that Mycoplasma resistance to macrolides can be quickly selected in vitro, and thus, providing that similar results could be obtained under field conditions, that development of resistance to these antibiotics in vivo might also be a relatively frequent event.

Antimicrobial susceptibility of Streptococcus suis isolated from swine in France and from humans in different countries between 1996 and 2000

The susceptibility of 135 Streptococcus suis strains isolated from pigs (n = 110) and from humans (n = 25) to 13 antimicrobial agents was studied by microdilution and disc diffusion methods using Mueller-Hinton Agar II (MH) supplemented with either defibrinated sheep blood (MHSB) or horse serum (MHHS). Results were similar for both methods used except for penicillin G whose zone diameters were reduced with MHSB compared with MHHS. When MH was supplemented with sheep blood, 39% of S. suis strains classified as penicillin susceptible by MHHS microdilution showed intermediate susceptibility. Nearly all strains were susceptible to penicillin G (except by disc diffusion in MHSB), amoxicillin, ceftiofur, florfenicol, gentamicin and bacitracin. The least active antimicrobial agents were doxycycline and macrolides/lincosamides. High-level resistance (MIC > 500 mg/L or zone diameters < 10 mm) to streptomycin and kanamycin was detected in only a few strains. The virulence of strains did not seem to be related to antimicrobial resistance because no statistical difference was reported between the proportion of resistant strains of S. suis isolated from pigs with meningitis, septicaemia and arthritis, and those from tonsils and nasal cavities. However, significant differences were found in the proportions of macrolide- or doxycycline-resistant strains between S. suis serotype 2 and other serotypes. The results of antibiotic susceptibility testing presented in this study indicate that beta-lactams can be used in empirical treatment of human and pig S. suis infections in France.

Plasma haptoglobin concentration in swine after challenge with Streptococcus suis

Eight 15-week-old pigs, reared under specific pathogen-free conditions, were inoculated with Streptococcus suis serotype 2. The animals were monitored before and after challenge by measuring rectal temperature, recording specific clinical symptoms and collecting blood samples for haptoglobin determination. Twenty-four hours after infection, the average haptoglobin plasma concentration of the animal group increased significantly and reached a maximum 4 days post-inoculation, followed by a constant mean level until the end of the trial on day 10. In spite of individual differences between the animals, an increase in haptoglobin concentration of at least 2.5 times above normal was observed in all infected pigs 1 day after challenge. Twenty-four hours after challenge, lameness was observed in five animals and an elevated body temperature was observed in seven of the eight experimental infected animals. These are the classical clinical symptoms of streptococcal infection. Haptoglobin was shown to increase in acute S. suis infection in pigs.

Characterization of mutations in DNA gyrase and topoisomerase IV Involved in quinolone resistance of Mycoplasma gallisepticum mutants obtained in vitro

Mycoplasma gallisepticum enrofloxacin-resistant mutants were generated by stepwise selection in increasing concentrations of enrofloxacin. Alterations were found in the quinolone resistance-determining regions of the four target genes encoding DNA gyrase and topoisomerase IV from these mutants. This is the first description of such mutations in an animal mycoplasma species.

Experimental airborne transmission of Streptococcus suis capsular type 2 in pigs

Experimental airborne transmission of Streptococcus suis type 2 was studied in specific pathogen free piglets. Forty piglets were allotted to five groups of eight 7-week-old animals and housed in three separated units. Negative control pigs (group 1) were housed in unit A and infected batches were housed in units B (group 2) and C (groups 4). In units B and C, non-inoculated groups (groups 3 and 5, respectively), 40 cm distant from the respective inoculated group and without any physical contact between them, also took place. Six animals of groups 2 and 4 were inoculated intravenously with 2 x 10(8) colony forming units (cfu) of a mild and a high virulent S. suis strains, respectively. The remaining animals in these groups and pigs from groups 1, 3, 5 received broth medium in the same way. Differences among virulence of S. suis capsular type 2 were observed in inoculated pigs of groups 2 and 4. Pigs from group 2 became carriers, showing only mild symptoms. By contrast, animals from group 4 presented an acute form of the disease. All the indirect contact pigs in groups 3 and 5 had S. suis in palatine tonsils from day 6 after the infection and they presented clinical manifestations similar to those observed in experimentally infected pigs. Two direct contact animals were also contaminated in the upper respiratory tract but surprisingly they did not show any symptoms. Airborne transmission of S. suis in experimentally pigs was demonstrated in the present study. Indirect infections, as described in this study, are a more realistic way to infect pigs than other experimental procedures and may be used to further study the pathogenesis of the infection caused by this important pathogen.

Experimental infection of specific pathogen free piglets with French strains of Streptococcus suis capsular type 2

A standardized model of Streptococcus suis type 2 infection in specific-pathogen-free piglets, housed in high-security barns, was used to compare the virulence of 3 French field strains of S. suis serotype 2 isolated from tonsils of a healthy pig (strain 65) or from diseased pigs (meningitis, strain 166', or septicemia, strain 24). In one of the 2 trials, 7-week-old pigs, in 3 groups of 8, were inoculated intravenously with 2 x 10(8) colony-forming units of S. suis type 2. In each group, 1 uninfected animal was a sentinel. Eight animals were also used as negative control group. The experiment was repeated under similar conditions with strains 65 and 166'. Virulence differed markedly among these S. suis strains when clinical signs, zootechnical performances, lesions, and bacteriological data were analyzed. Strain 65 did not induce clinical signs in inoculated pigs. In contrast, pigs infected with the other 2 strains exhibited clinical signs and typical lesions of S. suis type 2 infections. Differences in virulence were also observed between the 2 virulent strains. Sentinel animals exhibited the same manifestations as those recorded in inoculated piglets. Results were similar in the second trial, indicating that under the present experimental conditions, results were reproducible. The standardized conditions described in this study could be a useful tool to further study about the S. suis infection.

Seroepidemiology of Mycoplasma hyopneumoniae in pigs from farrow-to-finish farms

A prospective study was carried out on three intensive farrow-to-finish farms. The aims were to estimate the incidence of Mycoplasma hyopneumoniae infection, to determine when pigs become infected and the pattern of transmission of infection and to verify the relationship between seroconversion and clinical signs. One batch of pigs per farm was followed from farrowing-to-slaughter. Blood samples were taken at 10, 27, 70, 94, 125 and 147 days of age, from 44, 48 and 44 pigs per farm. Colostrum and blood samples were also taken from the sows. Animals were checked clinically once a week and coughing rates were recorded. Antibodies against M. hyopneumoniae were detected by a blocking ELISA. At 27, 70 and 94 days of age most pigs on the three farms were seronegative, suggesting that no circulation of M. hyopneumoniae occurred during the growing period. Thereafter, a high proportion of pigs seroconverted, indicating that infection occurred soon after the transfer of the animals to the finishing houses. Differences were detected between farms in the incidence of seroconversion. Seropositive pigs were widely distributed among the finishing pens, suggesting that in addition to direct contact, other methods of transmission, such as indirect or airborne transmission, may have been important. Coughing started at around the same time as seroconversion. The results showed that the critical period for the transmission of M. hyopneumoniae is around the beginning of the finishing period, when pigs have low concentrations of antibodies against the agent.

Development of a blocking enzyme-linked immunosorbent assay for detection of turkey antibodies to Mycoplasma meleagridis

A blocking enzyme-linked immunosorbent assay (B-ELISA) was developed to detect antibodies to Mycoplasma meleagridis (MM) in turkey sera. This assay was based on two mouse monoclonal antibodies recognising all MM strains tested but none of seven avian mycoplasmal species tested. Furthermore, their binding to the Tween 20 antigen was inhibited by serum from MM-infected birds. The B-ELISA test format was optimized. The cut-off was determined using a set of sera from MM-free turkeys. This B-ELISA was then compared with a commercial indirect ELISA (I-ELISA). Specificities of the two ELISA tests were not significantly different (100 or 99%, respectively). The sensitivity of B-ELISA was significantly higher than the I-ELISA when I-ELISA suspicious results were considered as negative. Testing sera from experimentally MM-infected animals showed that serum plate agglutination (SPA) test detected positive birds before both ELISA methods. Samples were collected in MM-infected commercial flocks and analyzed by SPA, ELISAs, MM-PCR or culture. Results showed that the sensitivity of the B-ELISA appeared superior to the I-ELISA. Moreover, the ability to detect maternal antibodies makes it a useful tool for eradication or control of MM infections.

Antigen heterogeneity and epitope variable expression in Mycoplasma meleagridis isolates

Immunoblotting was used to check the antigenic profiling of 27 Mycoplasma meleagridis strains isolated in different countries. Hyperimmune polyclonal rabbit antiserum as well as monoclonal antibodies (MAbs) raised against M. meleagridis (MM) showed antigen heterogeneity among strains. Five anti-MM MAbs were selected for lack of reaction against heterologous avian mycoplasma. Three of these five Mabs did not cross-react with 63 mycoplasma strains from six species affecting turkeys other than M. meleagridis. The five Mabs used to analyse the epitopes of 30 M. meleagridis strains indicated that some epitopes were not expressed in all strains. Moreover, other epitopes were located on proteins which differed according to number or molecular mass from strain to strain. The five Mabs therefore, recognised variable surface proteins, among which two were amphiphilic membrane proteins. Three of the selected Mabs recognised 29 or 30 of the 30 tested strains. The in vitro expression of surface epitopes in M. meleagridis ATCC 25284 was investigated by colony immunobinding and allowed demonstration of a variable antigenic system.

Use of an internal control in a nested-PCR assay for Mycoplasma hyopneumoniae detection and quantification in tracheobronchiolar washings from pigs

We have previously reported a nested PCR assay for the detection of Mycoplasma hyopneumoniae directly in tracheobronchiolar washings from living pigs in field conditions. Here, we describe the construction and use of an internal control to monitor the presence of PCR inhibitors. A PCR modified target DNA was constructed by insertion of a small DNA fragment into the M. hyopneumoniae specific DNA target. We have demonstrated that the internal control failed to be amplified in only three tracheobronchiolar washings samples out of the 362 tested. This control molecule was inserted in a Spiroplasma citri derived plasmid vector and introduced into S. citri cells by electroporation. After a few passages we ensured that the recombinant plasmid became inserted into the genome of S. citri. PCR amplification of the DNA of this transformed S. citri strain using nested PCR primers led to amplification of a 900-bp fragment which can be discriminated from the M. hyopneumoniae PCR product 700 bp. The S. citri transformants with the integrated internal control were added to the tracheobronchiolar washings prior to PCR and used as an internal control to check the efficiency of sample processing, and to demonstrate the presence of inhibitors. Furthermore, we have been able to estimate the number of mycoplasma cells in the tracheobronchiolar washings. Quantitation was performed by comparing the PCR signal intensity of the specific M. hyopneumoniae template with known concentrations of the S. citri competitor. The titer in tracheobronchiolar washings ranged approximatively from 10(4)to 10(8)M. hyopneumoniae cells per ml of clinical specimen. Quantitative PCR can be a useful tool for monitoring the progression of M. hyopneumoniae in the disease process.

A nested PCR assay for the detection of Mycoplasma hyopneumoniae in tracheobronchiolar washings from pigs

A nested polymerase chain reaction (PCR) was developed for the detection of Mycoplasma hyopneumoniae, the etiological agent of enzootic pneumonia, in tracheobronchiolar washings from live pigs. Two nested pairs of oligonucleotide primers were designed from the sequence of a specific DNA probe (I 141; accession number U02537). The primer combination was Hp1/Hp3 for the first step PCR while the nested primers (Hp4/Hp6) allowed amplification of a 706 bp fragment. All strains of M. hyopneumoniae tested in this study could be detected by the nested PCR. DNA from other bacterial species isolated from the respiratory tract of pigs or from other mycoplasmal species were not amplified. The detection limit was estimated to be 1 fg, corresponding approximately to one organism, while in the one step PCR previously described 4 x 10(2) organisms were required. The nested PCR was evaluated on 362 tracheobronchiolar lavages collected from pigs at 2, 4 and 6 months of age in eight herds chronically infected with M. hyopneumoniae. The nested PCR was compared to a blocking ELISA performed with sera collected from the same pigs at the same ages, and to an immunofluorescence test at slaughter on 65 lungs from 6-month old pigs. The comparison indicated that the nested PCR was significantly (p<0.05) more sensitive (157 positive results of 362 samples) than ELISA (118 positive results of 362 samples) for detection of M. hyopneumoniae infection. Nested PCR was also significantly more sensitive (54 positive results of 65 samples) than immunofluorescence (29 positive results of 65 samples) for detection of M. hyopneumoniae in pig lungs at slaughter. Moreover, the nested PCR was used to confirm the absence of the mollicute in a pig herd without any history of M. hyopneumoniae infection. Thus, nested PCR appears to be a useful test to assess M. hyopneumoniae infection on pig farms.

Production of muraminidase-released protein (MRP), extracellular factor (EF) and suilysin by field isolates of Streptococcus suis capsular types 2, 1/2, 9, 7 and 3 isolated from swine in France

A total of 323 isolates of Streptococcus suis recovered from diseased or healthy pigs in France were serotyped. The presence of virulence-related proteins, Muraminidase-Released Protein (MRP), Extracellular Factor (EF) and Suilysin was also studied in 122 isolates of capsular types 2, 1/2, 9, 7 and 3 to evaluate their implication in virulence of S. suis. Capsular types 2, 1/2, 9, 7 and 3 were the most frequently detected (93%), with 69% for the capsular type 2 alone. Capsular types 2, 1/2, 9, 7, 3, 1, 4, 8, 18, 10 and 12 were isolated from diseased pigs, whereas types 2, 7, 9, 1/2, and 3 originated from the nasal cavities or tonsils of healthy animals. Most of the S. suis type 2 isolates recovered from diseased pigs carried MRP+ EF- Suilysin- (46%) or MRP+ EF+ Suilysin+ (28%) phenotypes. The MRP+ EF- Suilysin- phenotype was also detected in 67% of S. suis type 2 strains isolated from healthy pigs. The production of the virulence-related proteins was less frequently found in S. suis types 1/2, 9, 7 and 3 recovered either from diseased or healthy pigs. In this study, all the capsular type 1/2 strains were MRP+ EF- Suilysin- and all the S. suis type 7 harboured an MRP- EF- Suilysin- phenotype. The MRP- EF- Suilysin- phenotype was found in S. suis types 2, 3, 7 and 9 isolated from septicaemia, meningitis, pneumonia, and pleurisy. These results suggest that the presence of these proteins should not be used as a single condition for classifying the virulence of a field isolate in France.

A PCR assay used to study aerosol transmission of Actinobacillus pleuropneumoniae from samples of live pigs under experimental conditions

The study describes a polymerase chain reaction (PCR) assay for the detection of Actinobacillus pleuropneumoniae. The test is based on the amplification of the omlA gene coding for an outer membrane protein of A. pleuropneumoniae. To test the specificity of the reaction, 19 other bacterial species related to A. pleuropneumoniae or isolated from pigs were assayed. They were all found negative in the PCR assay. The detection threshold of the test was 10(2) A. pleuropneumoniae CFU/assay. The test was then applied to the detection of A. pleuropneumoniae from tonsillar biopsies and tracheobronchial lavage fluids of pigs without a culture step. The detection of A. pleuropneumoniae in these samples was performed by PCR, by conventional culture and by bacteriology with immunomagnetic beads. The number of samples that were found positive by PCR was almost three times higher than the number of samples from which A. pleuropneumoniae was isolated by both bacteriological techniques. The detection of A. pleuropneumoniae in these samples allowed us to demonstrate its aerosol transmission to pigs under experimental conditions. The trial involved 18 specific pathogen free pigs. Six pigs, infected with A. pleuropneumoniae, were located in a unit A, together with four non-infected animals (contact pigs). Eight non-infected pigs (reporter pigs) were located in a unit B, adjacent to A. We detected A. pleuropneumoniae in samples from infected animals but also from 'contact' (unit A) and 'reporter' (unit B) pigs. The results of this study show that the simple preparation of the samples followed by the PCR assay may be a useful tool for epidemiological studies.

Isolation and characterization of a capsule-deficient mutant of Actinobacillus pleuropneumoniae serotype 1

The capsular polysaccharides (CPS) play a major role in pathogenicity of Actinobacillus pleuroIpneumoniae, the causative agent of porcine pleuropneumonia. The purpose of the present study was to isolate a mutant in CPS biosynthesis by using a mini-Tn 10 transposon mutagenesis system and evaluate its adherence to host cells. One mutant apparently did not possess CPS as it did not react with a monoclonal antibody against A. pleuropneumoniae serotype 1 capsular antigen. Absence of capsule was confirmed by flow cytometry and also by transmission electron microscopy after polycationic ferritin labelling. The site of insertion of the mini-Tn 10 was determined and found to be in the cpxC gene. Its gene product, CpxC, is a protein involved in polysaccharide transport across the cytoplasmic membrane during CPS biosynthesis. Use of piglet tracheal frozen sections indicated that the CPS mutant adhered significantly (P=0.0001) more than the parent strain. The non-capsular mutant was less virulent in pigs compared to the parent strain and showed no mortality in experimentally infected pigs. The CPS mutant was however resistant to pig serum. This CPS mutant is the first A. pleuropneumoniae mutant in a CPS transport gene. It is also the first time that adherence of a CPS mutant of A. pleuropneumoniae is evaluated. Our observations indicate that capsular polysaccharides of A. pleuropneumoniae serotype 1 are not involved in adherence to piglet tracheal frozen sections but rather mask, at least in part, the adhesive functions.

Experimental aerosol transmission of Actinobacillus pleuropneumoniae to pigs

In order to demonstrate the possible role of aerosol in the transmission of Actinobacillus pleuropneumoniae, an experiment including 18 specific pathogen-free (SPF), 10-week-old piglets, randomly distributed into 2 adjacent units, was carried out. In these facilities, air was forced through absolute filters to prevent any contact with infectious agents. During the first 6 d post inoculation, the 2 units were connected by a rectangular opening and the air circulation was forced by the ventilation system from unit A (inoculated pigs) to unit B (non-inoculated pigs). The A. pleuropneumoniae strain (biovar 1 serovar 9) was isolated in France from an outbreak of porcine pleuropneumonia. Two different infecting doses, 10(7) cfu/animal and 10(8) cfu/animal, were inoculated by intranasal route in 6 pigs of unit A. The infection spread quickly from the inoculated pigs to the non-inoculated pigs. Clinical signs were acute during the 4 d post inoculation: hyperthermia, respiratory distress and, sometimes, death (6 pigs of the unit A and 2 pigs of the unit B). All pigs seroconverted against A. pleuropneumoniae serovar 9 within 2 weeks. Lung lesions were severe: fibrinous pleurisy and lung hemorrhages in the acute stage, pleural adherences and focal pulmonary necrosis in the chronic stage. Actinobacillus pleuropneumoniae was isolated from the tonsils and/or lungs in 16 animals. It could be also isolated from the air of the experimental unit. This study showed that A. pleuropneumoniae was readily transmitted through aerosol over a distance of at least 2.5 m.

Isolation and characterization of mini-Tn10 lipopolysaccharide mutants of Actinobacillus pleuropneumoniae serotype 1

Lipopolysaccharide (LPS) has previously been identified as the major adhesin of Actinobacillus pleuropneumoniae involved in adherence to porcine respiratory tract cells. The purpose of the present study was to isolate and characterize mutants in LPS biosynthesis by using a mini-Tn10 transposon mutagenesis system. Seven mutants appeared to possess a rough LPS (among which two had similar Southern blot profiles) while one mutant (#5.1) expressed the high-molecular-mass LPS, but as visualized by Tricine SDS-PAGE, showed an additional band in the core-lipid A region. The LPS mutants showed sensitivity to pig serum to various degrees, while the parent strain was serum-resistant. Use of piglet frozen tracheal sections indicated that, surprisingly, the rough LPS mutants adhered similarly or in greater numbers than the parent strain. However, the LPS mutant #5.1 adhered significantly less than the parent strain and was also less virulent in pigs. The gene affected by mini-Tn10 in LPS mutant #5.1 is galU, the structural gene for UTP-alpha-D-glucose-1-phosphate uridylyltransferase, involved in LPS core biosynthesis. Complementation analysis confirmed that the phenotypic characteristics of LPS mutant #5.1 are the result of the inactivation of the galU gene. Our data suggest that although the presence of O-antigen does not seem to be essential, an intact core-lipid A region might be required for adherence of A. pleuropneumoniae to porcine respiratory tract cells. To the best of our knowledge, these mutants represent the first isogenic mutants of A. pleuropneumoniae defective in LPS biosynthetic genes.

Genomic relatedness among Actinobacillus pleuropneumoniae field strains of sterotypes 1 and 5 isolated from healthy and diseased pigs

Forty-four Actinobacillus pleuropneumoniae isolates recovered from both healthy and diseased pigs were characterized by random amplified polymorphic DNA analysis (RAPD), pulsed field gel electrophoresis (PFGE) and apx toxin gene typing. Nine RAPD types and 14 PFGE patterns were identified. No common RAPD or PFGE patterns were found between strains of serotype 1 and those of serotype 5. The RAPD analysis indicated that the 15 serotype 1 strains isolated from diseased pigs were assigned to 4 RAPD types, with 66% of strains characterized by the same RAPD type. By contrast, the 5 strains of serotype 1 isolated from healthy carriers were dispersed in 4 RAPD types. These data suggest that the diversity of strains isolated from healthy pigs could be higher than that of strains recovered from diseased pigs. In addition, all serotype 5 strains exhibited a unique RAPD type. Unlike RAPD, PFGE analysis allowed discrimination among isolates of serotype 1 and among those of serotype 5. All but 3 isolates showed the same apx genotype as their respective serotype reference strain. These data indicate that RAPD analysis is a valuable rapid tool for routine subtyping of strains of serotype 1. For strains of serotype 5, a combination of several typing methods, such as PFGE and apx gene typing, is needed to provide useful information on the molecular epidemiology of swine pleuropneumonia.

Chromosome sizes and phylogenetic relationships between serotypes of Actinobacillus pleuropneumoniae

The genome size of Actinobacillus pleuropneumoniae was determined by pulsed field gel electrophoresis of AscI and ApaI digested chromosomal DNA. The genome size of the type strain 4074T (serotype 1) was determined to be 2404 +/- 40 kb. The chromosome sizes for the reference strains of the other serotypes range between 2.3 and 2.4 Mb. The restriction pattern profiles of AscI, ApaI and NheI digested chromosomes showed a high degree of polymorphism among the different serotype reference strains and allowed their discrimination. The analysis of the macrorestriction pattern polymorphism revealed phylogenetic relationships between the different serotype reference strains which reflect to some extent groups of serotypes known to cross-react serologically. In addition, different pulsed fields gel electrophoresis patterns also revealed heterogeneity in the chromosomal structure among different field strains of serotypes 1, 5a, and 5b, while strains of serotype 9 originating from most distant geographical places showed homogeneous ApaI patterns in pulsed field gel electrophoresis.

Swine mycoplasmoses

Mycoplasma hyopneumoniae is the primary agent of enzootic pneumonia in pigs. The lung lesions, generally observed in young pigs, are characterised by a hyperplasia of the epithelial cells and an increased perivascular and peribronchiolar accumulation of mononuclear cells. Following M. hyopneumoniae infection, immune reactions are observed and resistance is induced in pigs. Laboratory diagnosis is generally performed by an immunofluorescent test and by enzyme-linked immunosorbent assay. Antibiotics are useful but the development of resistance has been described. Vaccination seems to be an effective method of controlling the disease. M. hyorhinis, generally transmitted by sows to piglets through nasal secretions, exists in a high percentage in the respiratory tract of healthy pigs. But some strains can induce serofibrinous to fibrinopurulent polyserositis and arthritis. M. hyorhinis is isolated from acute and subacute phase lesions and serum antibodies are detectable. M. hyosynoviae has a special affinity for joint tissue and may cause arthritic disease, leading to economic losses. This mycoplasma is generally located in the tonsils. Piglets are infected by sows after four to six weeks of life. Evidence of disease occurs in animals of between 30 to 40 kg and 100 kg, and bursae and joints are affected. A non-suppurative viscous fluid of a serofibrinous/serosanguineous nature is reported. In chronic cases, the synovial membrane is affected. M. hyosynoviae is isolated from the joints and pharyngeal/tonsillar samples and can induce antibodies in blood and joint fluid. Predisposing factors play an important role. M. flocculare is widely distributed in swine, in normal and pneumonic lungs and in nasal cavities, but no pathogenic capability has been described. There is great interest in this mycoplasma because of the great similarity to M. hyopneumoniae.

Detection of antibodies against Streptococcus suis capsular type 2 using a purified capsular polysaccharide antigen-based indirect ELISA

In the present study a purified capsular polysaccharide antigen-based indirect ELISA (CPS-ELISA) to detect antibodies against Streptococcus suis capsular type 2 was developed and compared with a whole cell antigen-based ELISA (WCA-ELISA). The WCA-ELISA presented a very low specificity when rabbit antisera to other capsular types were tested. Most of these cross-reactions were due to common proteins. The standardized CPS-ELISA gave satisfactory results using a concentration of 0.1 micrograms/well; most cross-reactions decreased significantly, with some exceptions, such as those shared by capsular types 1/2, 12 and 17. These cross-reactions were mainly due to common epitopes present in the capsule, as shown by immunoblotting. In a second experiment, the CPS-ELISA was used to detect antibodies in experimentally infected piglets. Despite the fact that capsular type 2 S. suis could be reisolated from all infected animals during and/or after the trial, antibody titers against a second infection. Sera from piglets experimentally infected were completely protected against a second infection. Sera from piglets experimentally infected with S. suis capsular types 1/2 or 12 presented cross-reactions at low dilutions, confirming data previously obtained with rabbit sera. Finally, sera of animals from herds with clinical signs associated with S. suis capsular type 2 did not present titers significantly different from those of disease free herds. From our results we concluded that the CPS-ELISA developed in this study can not be used as a diagnostic tool to identify infected animals.

Analysis of putative ABC transporter genes in Mycoplasma hyopneumoniae

A previously described DNA probe specific for Mycoplasma hyopneumoniae (I-141) was fully sequenced and found to consist of 1618 bp and to contain two tandemly repeated ORFs. The deduced amino acid sequence of the two ORFs showed significant homologies with ATP-binding cassette (ABC) transporter proteins, particularly those of the eukaryotic multidrug resistance (MDR) protein family (up to 21% identity and 47% similarity). A somewhat lower homology was evident with the secretion protein HlyB of the RTX-haemolysin from Escherichia coli. The location of the two ORFs on the M. hyopneumoniae chromosome was downstream of the rrl gene encoding the 23S rRNA, but transcribed in the opposite direction. PCR amplification and subsequent chromosomal analysis by Southern blot hybridization of several M. hyopneumoniae strains showed that all field strains contained the two putative ABC transporter genes. However, some culture collection strains derived from strain J had lost these genes as the result of a 2221 bp deletion.

Role of capsular sialic acid in virulence and resistance to phagocytosis of Streptococcus suis capsular type 2

Streptococcus suis capsular type 2 has a capsule rich in sialic acid (NANA). Sialic acid, known to be an antiphagocytic factor for many bacterial species, inhibits the activation of the alternative complement pathway. The role of capsular NANA in virulence, resistance to phagocytosis and intracellular survival of S. suis capsular type 2 was evaluated. In general, a low concentration of NANA was observed for all the S. suis strains tested. In addition, no difference could be found in NANA concentrations between strains of different virulence degrees. Sialic acid concentration increased in the virulent strain 89-1591 and the avirulent strain 90-1330 after in vivo growth with an increased capsular material thickness compared to growth in vitro. No significant difference could be found in the phagocytosis rate by porcine blood monocytes of either strain and strain 89-1591 treated with sialidase or the sialic acid-binding lectin from Sambucus nigra (SNA I). Intracellular survival of strain 89-1591 decreased after treatments with sialidase or lectin, becoming comparable to that of strain 90-1330. Finally, no difference could be seen in virulence using a murine model, even if strain 89-1591 was treated with the enzyme or the lectin. Thus, NANA does not seem to be a critical virulence factor for S. suis capsular type 2.

Polymerase chain reaction for Mycoplasma hyopneumoniae detection in tracheobronchiolar washings from pigs

We have used the polymerase chain reaction (PCR) to detect Mycoplasma hyopneumoniae in tracheobronchiolar washings collected from experimentally infected piglets. On the basis of the published nucleotide sequence of M. hyopneumoniae I141 probe (accession number U02537), primers were chosen to produce an amplified fragment of 1561 bp. All the M. hyopneumoniae strains tested could be detected by the PCR test. DNA from other mycoplasmal and bacterial species currently isolated from respiratory tract of piglets gave negative result. The detection limit was estimated to be 500 fg of purified DNA corresponding to 4.10(2) organisms. The sensitivity of PCR reaction was also evaluated on microorganisms in culture, the limit sensitivity was 2.5 10(3) organisms. In the present study, a total of 143 tracheobronchiolar washings collected from experimentally infected piglets were submitted to PCR. For each tracheobronchiolar washing, PCR was performed on crude extracts treated with lysis buffer and on extracted DNA. The PCR results obtained with the two kinds of samples were compared to the immunofluorescence (IF) results. This comparison indicates a good correlation between PCR and IF test in 121/143 cases. The presence of M. hyopneumoniae is revealed in 19/143 of the washing samples only by PCR. In our hand, PCR appears to be the more sensitive test to detect M. hyopneumoniae in experimentally infected piglets.

Immune response against the L-lactate dehydrogenase of Mycoplasma hyopneumoniae in enzootic pneumonia of swine

The L-lactate dehydrogenase (LDH) of Mycoplasma hyopneumoniae, formerly named protein P36, belongs to the predominant immunogenic proteins in pigs which were naturally or experimentally infected with M. hyopneumoniae. The antigenic reaction against M. hyopneumoniae LDH has been shown to be species specific. Recombinant M. hyopneumoniae LDH, which was genetically engineered to contain six histidine residues at its C-terminal end, was expressed in E. coli and purified to a high degree using Ni-chelate affinity chromatography. The genetically engineered LDH still showed the same biochemical activity and immunological specificity as the wild-type LDH and was used as an antigen for a M. hyopneumoniae LDH ELISA. Using this assay, we showed that pigs experimentally infected with M. hyopneumoniae raised antibodies against LDH in two steps. An early, relatively weak anti-LDH response was detected between 5 to 10 weeks post-infection when clinical signs and lung lesions occur. This first minor raise of anti-LDH antibodies occurred simultaneously with the strong appearance of antibodies against an antigen consisting of membrane proteins of M. hyopneumoniae prepared with Tween 20 extraction. A second, strong raise in anti-LDH antibodies was observed from the twelfth week after infection, at a time when the disease signs and the infectious agent disappeared. The high anti-LDH titer persisted until 21 weeks post-infection, in contrast to the antibody titer against the membrane proteins which started to decrease after its peak at 12 weeks post-infection. A LDH-ELISA may also be useful for detecting past infections.

A blocking ELISA using a monoclonal antibody for the serological detection of Mycoplasma hyopneumoniae

A blocking ELISA was developed by using a monoclonal antibody (4082-05-344-18) which specifically detected an epitope on the Mycoplasma hyopneumoniae 40 kDa membrane protein without cross-reacting with M flocculare or M hyorhinis. The results obtained with sera from specific pathogen-free pigs inoculated with M flocculare or M hyorhinis confirmed the specificity of the assay. An immunoblotting procedure was used to characterise the antibody response of pigs experimentally infected with M hyopneumoniae. Antibodies to the 40 kDa antigen were detected two weeks after infection and remained as major markers for at least 20 weeks. Cross-reacting antibodies to this antigen were not detected in convalescent sera from piglets infected with M flocculare or M hyorhinis. Sera from experimentally infected pigs were compared by means of the blocking ELISA and an indirect ELISA. The kinetics of ELISA antibodies after experimental inoculation were also studied. The detection of antibody was rather more stable for a longer time with the blocking ELISA than with the indirect ELISA. In an evaluation of more than 1000 sera from the field there was excellent agreement between the two methods.

Virulence of capsulated and noncapsulated isolates of Pasteurella multocida and their adherence to porcine respiratory tract cells and mucus

The virulence and the adherence to porcine respiratory tract cells and mucus of three toxigenic, capsular type D Pasteurella multocida isolates and their noncapsulated variants were evaluated in the present study. Loss of capsule by P. multocida, verified by transmission electron microscopy after polycationic ferritin labeling, was associated with a massive reduction in virulence of the organisms in mice. Specific-pathogen-free piglets inoculated intranasally with one of the capsulated isolates or its noncapsulated variant developed turbinate lesions characterized by bone resorption and by an inflammation of the mucosa associated with hyperplasia and squamous metaplasia of the epithelium. Infection with the capsulated isolate led to more severe lesions and atrophy of turbinates. The interactions of these P. multocida isolates with porcine respiratory tract cells and mucus were studied in vitro. The presence of capsule resulted in a decrease in binding of respiratory tract mucus were studied in vitro. The presence of capsule resulted in a decrease in binding of respiratory tract mucus to P. multocida isolates as determined by a dot blot assay. The presence of capsule also resulted in a significant decrease in adherence to porcine tracheal rings maintained in culture. The capsule seemed to mask outer membrane components which are involved in adherence. One of these components might be lipopolysaccharide since purified lipopolysaccharide bound respiratory tract mucus and blocked adherence of this microorganism to porcine tracheal rings. Our data indicate that capsular material does not seem to be involved in adherence of P. multocida to respiratory tract cells and mucus, but capsulated isolates are more virulent in mice and also in piglets.

Serological characterisation of Actinobacillus pleuropneumoniae strains of serotypes 1, 9 and 11

Various serological tests such as agglutination, coagglutination, indirect haemagglutination, immunodiffusion and counterimmunoelectrophoresis were used to characterise serologically Actinobacillus pleuropneumoniae isolates of serotypes 1, 9 and 11 using rabbit hyperimmune sera against serotypes 1 to 12. The rapid slide agglutination test using whole-cell suspension and the indirect haemagglutination test using whole-cell saline extract as antigens gave type specific reactions for serotypes 1 and 9. Antigens comprising saline extracts of boiled or autoclaved cells demonstrated common epitopes among the isolates of all three serotypes in the indirect haemagglutination test. Quantification of the type and group-specific antigens by the coagglutination test. Quantification of the type and group-specific antigens by the coagglutination test distinguished serotypes 1 and 9 strains from those of serotype 11. Results of absorption studies in immunodiffusion tests indicated that the cross-reactivity encountered among strains of serotypes 1, 9 and 11 might be due to common epitopes associated with cell-wall antigens. However, they certainly also have type-specific epitopes, possibly associated with superficially located, capsular antigens.

A specific DNA probe for detecting Mycoplasma hyopneumoniae in experimentally infected piglets

Mycoplasma hyopneumoniae is the primary agent of swine enzootic pneumonia. Because of fastidious growth requirements and its serological cross-reactions with other porcine mycoplasmas, we developed a specific DNA probe for its detection. A partial genomic library of M. hyopneumoniae was constructed in plasmid pBR 322 using Hind III chromosomal fragments. The recombinant plasmids were screened by differential hybridization with M. flocculare and M. hyorhinis genomic DNA probes. One non-hybridizing recombinant plasmid was selected and its 1.65 kbp insert (designated I141) tested for specificity against genomic DNA from numerous mycoplasmas, other bacteria species and DNA from lung tissue of specific pathogen free (SPF) piglets. The 32P labelled I141 could detect specifically down to 400 pg of M. hyopneumoniae genomic DNA. To test the suitability of the I141 probe for the laboratory diagnosis of M. hyopneumoniae infections, we used clinical tracheobronchial specimens from piglets which were experimentally infected with M. hyopneumoniae. The results with hybridization on each specimen were compared to findings with an immunofluorescence test. Of the clinical specimen tested, there was agreement in the two tests of 63%.

Electron microscopic observation of the respiratory tract of SPF piglets inoculated with Mycoplasma hyopneumoniae

Seven hysterectomy derived piglets were repeatedly challenged with Mycoplasma hyopneumoniae during the first week of life. Samples of trachea, bronchi and lung tissue collected 2-11 weeks post-inoculation (p.i.) were examined using light and electron microscopy. Autoradiography was used to study in more detail the site of M. hyopneumoniae multiplication. Gross lesions were observed in lung tissue and were characterized by hyperplasia of the epithelium and an increased mononuclear cell accumulation in perivascular and peribronchiolar areas. Mild lesions of the trachea and the bronchi, including epithelial hyperplasia and infiltration of the lamina propria by inflammatory cells, were noted. Electron microscopy showed that, 2-6 weeks p.i., changes in the mid-trachea and bronchi surface consisted of the loss of cilia. Mycoplasmas covered tufts of cilia remaining on the epithelial cell surface. Scanning and transmission electron micrographs showed that they were predominantly found closely associated with the top of cilia. No specialized terminal structure could be seen and no mycoplasma cells were identified lying free in the lumen nor in close contact with the plasma membrane of cells or microvilli. Some fine fibrils radiating from one mycoplasma to another or to cilia were seen at higher magnification by scanning electron microscopy. Six to eleven weeks p.i., a disrupted epithelial surface lacking cilia was observed. Cells were desquamated and shed into the lumen with cellular remains containing droplets of mucus. Autoradiography revealed that label corresponded to the observed mycoplasma distribution. At the top of cilia, a high density of labeling was visible in the zone of high mycoplasma concentration. Therefore, incorporation of the label in the mycoplasma is proof or their multiplication in the trachea. The intimate association between the mycoplasma and cilia may be an important factor in the pathogenesis of the disease caused by M. hyopneumoniae (swine enzootic pneumonia).

Immunological and pathological reactions in piglets experimentally infected with Mycoplasma hyopneumoniae and/or Mycoplasma flocculare

The aim of this work was to examine in vivo whether infection with Mycoplasma hyopneumoniae (M. hyop) and/or Mycoplasma flocculare (M. floc) would interact and influence the severity of enzootic pneumonia in piglets. Specific pathogen-free, hysterectomy-derived piglets were allocated to six groups and experimentally inoculated with M. hyop. and/or M. floc at the age of 2 or 8 weeks. Clinical symptoms, frequency of coughing and temperature measurement were noted daily. Lung lesions were recorded by post-mortem examination and histological observations. The cross-inoculation with both mycoplasmas did not influence the clinical or the pathological picture of the disease. Evolution of specific and crossreacting antibodies was analyzed by ELISA and immunoblotting. Animals inoculated with M. floc did not develop any lesions but showed a weak antibody response 6-8 weeks post-infection (p.i.). No cross-reacting antibodies against M. hyop proteins were detected. In animals inoculated with M. hyop, the first antibody response was detectable 4-5 weeks p.i. and was stronger in piglets infected at the age of 2 weeks than at the age of 8 weeks. Three cross-reacting antibodies against M. floc proteins with molecular weights of 110, 47 and 33 kDa were detected by antibodies to M. hyop. Experimental infections with both mycoplasmas did not show differences in the pattern of species-specific proteins.

Cloning and expression of a species-specific early immunogenic 36-kilodalton protein of Mycoplasma hyopneumoniae in Escherichia coli

Mycoplasma hyopneumoniae, the etiologic agent of porcine enzootic pneumonia, synthesizes a 36-kDa protein which is an early and strong immunogenic factor in experimentally and naturally infected swine. The gene encoding this protein was cloned by screening a gene library of M. hyopneumoniae DNA with rabbit hyperimmune serum made against whole M. hyopneumoniae cells and convalescent-phase swine serum. Analysis of the recombinant protein expressed in Escherichia coli by immunoblot techniques showed that the protein is expressed in E. coli in its full length and does not cross-react with proteins from M. flocculare or M. hyorhinis. Genetic analysis showed that the gene was expressed from the lac promoter of the vector and seems to be translationally initiated from its own ribosome binding site. Subcloning in a transcriptional fusion vector to optimize expression resulted in production of the 36-kDa protein in E. coli at levels up to 30% of total protein.

Identification of a 68-kilodalton outer membrane protein as the major protective antigen of Bordetella bronchiseptica by using specific-pathogen-free piglets

Maternal antibody to an outer membrane 68-kilodalton (kDa) protein of Bordetella bronchiseptica was shown to be protective in experiments on specific-pathogen-free piglets. After challenge with B. bronchiseptica, 100% (n = 19) control piglets from nonimmunized sows developed pneumonia, coughing, and sneezing, and 74% of the animals developed severe atrophic rhinitis. In 12 piglets from a sow immunized with 68-kDa protein, pneumonia occurred only in 34% of offspring, coughing was reduced, the duration of coughing bouts was shortened, and severe atrophic rhinitis occurred in one animal only (8%). The difference in the occurrence of atrophic rhinitis and of pneumonia in immunized and nonimmunized offspring was statistically significant (P less than 0.05). Sera of protected piglets had high titers (enzyme-linked immunosorbent assay) of antibodies that showed a high specificity for the 68-kDa protein isolated from B. bronchiseptica, whereas their reactivity with an analogous 69-kDa protein isolated from Bordetella pertussis was low or absent. The 68-kDa protein of B. bronchiseptica appeared to be the major protective antigen in B. bronchiseptica infection; however, isolated protein alone did not induce such a solid protection, as observed in a previous study after the application of an effective whole cell vaccine.

An evaluation in pigs of Nobi-Vac AR and an experimental atrophic rhinitis vaccine containing P multocida DNT-toxoid and B bronchiseptica

The trial involved eight large white sows obtained from a closed experimental specific pathogen free herd. Four sows (two each for an experimental vaccine and for Nobi-Vac AR) were vaccinated twice (eight weeks and two weeks before parturition) with 2 ml of vaccine administered intramuscularly. Two unvaccinated sows were used as an infected control group and two unvaccinated sows served as an uninfected control group. Forty-six piglets (28 from vaccinated sows and 18 from unvaccinated sows) were challenged by intranasal instillation of Bordetella bronchiseptica at two days of age and Pasteurella multocida type D, dermonecrotic toxin at seven days of age. Among the infected control group some piglets died and there were clinical signs of pneumonia and severe turbinate atrophy. In the vaccinated groups the results showed that immunisation of the pregnant sows had provided a good level of antibodies, which were transmitted to their offspring. There was a significant reduction in the clinical signs and no lesions were observed in the group vaccinated with the experimental vaccine and only moderate atrophy of the turbinates in the Nobi-Vac AR group. B bronchiseptica and P multocida were never recovered from the lungs of the vaccinated groups and in the nasal cavities their frequency declined with age.

The Mycoplasma hyopneumoniae plasma membrane as a vaccine against porcine enzootic pneumonia

From an economical standpoint, the colonization of the respiratory epithelium by Mycoplasma hyopneumoniae, the mollicute responsible for enzootic pneumonia in pigs which leads to a reduction in the weight gain/feed ratio, has serious consequences in very young animals; we show here that its is possible to efficiently protect these animals with the colostral antibodies raised in sows immunized during their gestation with M. hyopneumoniae BQ14 membranes. In an experiments using 9 sows and 75 piglets, the vaccinal preparation was found to protect 70 to 100% of the piglets (depending upon the presentation of the immunogen) as well as being totally innocuous. The best results were obtained with an adjuvant made of hydroxide aluminium gel. Of the piglets born to non-immunized sows, 8.3% exhibited typical pneumonic lesions. The vaccination procedure was found to enhance the elimination of M. hyopneumoniae from the respiratory tract of the piglets, as in 95% of the protected animals, the microorganisms could no longer be isolated. Conversely, M. hyopneumoniae was isolated from 89% of the piglets born to unvaccinated sows. A correlation was found between the protective effect and the rise in the titre of circulating antibodies directed against M. hyopneumoniae surface antigens. These results show that the plasma membrane of M. hyopneumoniae is a potential vaccine against porcine enzootic pneumonia. In particular, passively transmitted immunity via the colostrum provides the most precocious means of protection for the animals.

Comparison of enzyme-linked immunosorbent assay (ELISA) and indirect hemagglutination (IHA) in experimental Mycoplasma hyopneumoniae infection of pigs

Twenty-five hysterectomy-derived piglets were infected intratracheally at 16 days of age with a field strain of Mycoplasma hyopneumoniae. Twenty uninfected piglets constituted the control group. Clinical symptoms were noted daily and sera collected weekly. The 45 pigs were killed from 1 to 20 weeks after infection. M. hyopneumoniae induced a temperature response, coughing and pneumonia. After 10 weeks, a noticeable regression of the macroscopic lung lesions was observed. The infection was followed by an antibody response, and the antibody titers reflected the disease stages. ELISA appears to be the most sensitive procedure to detect early and late antibody production.

Evaluation of Bordetella bronchiseptica vaccines in specific-pathogen-free piglets with bacterial cell surface antigens in enzyme-linked immunosorbent assay

The progenies of specific-pathogen-free sows which had been immunized with Bordetella bronchiseptica vaccines of various origin before parturition were challenged intranasally with B. bronchiseptica within 5 days of birth. Sera of piglets were taken weekly and investigated by enzyme-linked immunosorbent assay against a mixture of B. bronchiseptica cell surface antigens containing curled fibers and fimbriae, lipopolysaccharide, and a mixture of proteins mostly derived from the outer membrane. The serological response to this antigenic mixture was paradoxical; the highest titers were obtained with the least effective vaccines. Antibodies which did relate to protection were oriented against the outer-membrane-derived proteins, one of which, of 68,000 molecular weight, appeared to be particularly important for two reasons. First, its concentration within the antigenic mixture was dependent upon cultural conditions; of all the proteins present in virulent strains, it was the first to disappear upon modulation. Second, it was absent from a strain which was unable to induce atrophic rhinitis in specific-pathogen-free piglets. Although all vaccines tested had some beneficial effect on the various clinical manifestations of the disease, only two vaccines were effective (P less than 0.001) in the prevention of nasal pathological changes. These two vaccines also stimulated the highest titers against the 68,000-molecular-weight protein. A mouse protection test utilizing a lethal intraperitoneal challenge failed to monitor the efficacy of vaccines for protection against atrophic rhinitis.