Antibody responses of swine following infection with Mycoplasma hyopneumoniae, M. hyorhinis, M. hyosynoviae and M. flocculare

Effect of pooled tracheal sample testing on the probability of Mycoplasma hyopneumoniae detection

Tracheal pooling for Mycoplasma hyopneumoniae (M. hyopneumoniae) DNA detection allows for decreased diagnostic cost, one of the main constraints in surveillance programs. The objectives of this study were to estimate the sensitivity of pooled-sample testing for the detection of M. hyopneumoniae in tracheal samples and to develop probability of M. hyopneumoniae detection estimates for tracheal samples pooled by 3, 5, and 10. A total of 48 M. hyopneumoniae PCR-positive field samples were pooled 3-, 5-, and 10-times using field M. hyopneumoniae DNA-negative samples and tested in triplicate. The sensitivity was estimated at 0.96 (95% credible interval [Cred. Int.]: 0.93, 0.98) for pools of 3, 0.95 (95% Cred. Int: 0.92, 0.98) for pools of 5, and 0.93 (95% Cred. Int.: 0.89, 0.96) for pools of 10. All pool sizes resulted in PCR-positive if the individual tracheal sample Ct value was < 33. Additionally, there was no significant decrease in the probability of detecting at least one M. hyopneumoniae-infected pig given any pool size (3, 5, or 10) of tracheal swabs. Furthermore, this manuscript applies the probability of detection estimates to various real-life diagnostic testing scenarios. Combining increased total animals sampled with pooling can be a cost-effective tool to maximize the performance of M. hyopneumoniae surveillance programs.

Dynamics of antibody response and bacterial shedding of Mycoplasma hyorhinis and M. hyosynoviae in oral fluids from experimentally inoculated pigs

Mycoplasma hyorhinis (Mhr) and M. hyosynoviae (Mhs) are commensal organisms of the upper respiratory tract and tonsils but may also cause arthritis in pigs. In this study, 8-week-old cesarean-derived colostrum-deprived (CDCD) pigs (n = 30; 3 groups, 10 pigs per group, 2 pigs per pen) were inoculated with Mhr, Mhs, or mock-inoculated with culture medium and then pen-based oral fluids were collected at different time points over the 56 days of the experimental study. Oral fluids tested by Mhr and Mhs quantitative real-time PCRs revealed Mhr DNA between day post inoculation (DPI) 5-52 and Mhs DNA between DPI 5-15. Oral fluids were likewise tested for antibody using isotype-specific (IgG, IgA, IgM) indirect ELISAs based on a recombinant chimeric polypeptide of variable lipoproteins (A-G) for Mhr and Tween 20-extracted surface proteins for Mhs. Mhr IgA was detected at DPI 7 and, relative to the control group, significant (p < 0.05) antibody responses were detected in the Mhr group between DPI 12-15 for IgM and DPI 36-56 for both IgA and IgG. In the Mhs group, IgM was detected at DPI 10 and significant (p < 0.05) IgG and IgA responses were detected at DPI 32-56 and DPI 44-56, respectively. This study demonstrated that oral fluid could serve as an effective and convenient antemortem sample for monitoring Mhr and Mhs in swine populations.

Characterizing the detection of inactivated Mycoplasma hyopneumoniae DNA in the respiratory tract of pigs

A positive Mycoplasma hyopneumoniae PCR result in a clinical specimen may eventually represent the mere detection of non-viable bacteria, complicating the diagnostic interpretation. Thus, the objective of this study was to evaluate the PCR detection of non-viable M. hyopneumoniae and its residual cell-free DNA in live pigs. Pigs were inoculated with either active or inactivated M. hyopneumoniae and were sampled for up to 14 days. Mycoplasma hyopneumoniae was not detected by PCR at any timepoint in pigs inoculated with the inactivated bacterium, suggesting that in healthy pigs, the non-viable M. hyopneumoniae DNA was rapidly sensed and cleared.

Establishment of a Mycoplasma hyorhinis challenge model in 5-week-old piglets

Introduction

Mycoplasma hyorhinis is an emerging swine pathogen with high prevalence worldwide. The main lesions caused are arthritis and polyserositis, and the clinical manifestation of the disease may result in significant economic losses due to decreased weight gain and enhanced medical costs. We aimed to compare two challenge routes to induce M. hyorhinis infection using the same clinical isolate.

Methods

Five-week-old, Choice hybrid pigs were inoculated on 2 consecutive days by intravenous route (Group IV-IV) or by intravenous and intraperitoneal routes (Group IV-IP). Mock-infected animals were used as control (control group). After the challenge, the clinical signs were recorded for 28 days, after which the animals were euthanized. Gross pathological and histopathological examinations, PCR detection, isolation, and genotyping of the re-isolated Mycoplasma sp. and culture of bacteria other than Mycoplasma sp. were carried out. The ELISA test was used to detect anti-M. hyorhinis immunoglobulins in the sera of all animals.

Results

Pericarditis and polyarthritis were observed in both challenge groups; however, the serositis was more severe in Group IV-IV. Statistically significant differences were detected between the challenged groups and the control group regarding the average daily weight gain, pathological scores, and ELISA titers. Additionally, histopathological scores in Group IV-IV differed significantly from the scores in the control group. All re-isolated strains were the same or a close genetic variant of the original challenge strain.

Discussion

Our results indicate that both challenge routes are suitable for modeling the disease. However, due to the evoked more severe pathological lesions and the application being similar to the hypothesized natural route of infection in Group IV-IV, the two-dose intravenous challenge is recommended by the authors to induce serositis and arthritis associated with M. hyorhinis infection.

Efficacy evaluation of a novel oral silica-based vaccine in inducing mucosal immunity against Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae, the main etiological agent of Porcine Enzootic Pneumonia, is widely spread in swine production worldwide. Its prevention is of great interest for the productive system, since its colonization in the lung tissue leads to intense production losses. This study aimed to compare the M. hyopneumoniae shedding and acute-phase response in 30 pigs submitted to different vaccination protocols: an experimental oral vaccine using a nanostructured mesoporous silica (SBA-15) as adjuvant (n = 10); an intramuscular commercially available vaccine at 24 days of age (n = 10); and a control group (n = 10) following experimental challenge with M. hyopneumoniae. Laryngeal and nasal swabs were collected weekly and oral fluids were collected at 7, 10, 14, 17, 23, 28, 35, 42, and 49 days post-infection to monitor pathogen excretion by qPCR. Nasal swabs were also used to detect anti-M. hyopneumoniae IgA by ELISA. Blood samples were collected for monitoring acute phase proteins. The antibody response was observed in both immunized groups seven days after vaccination, while the control group became positive for this immunoglobulin at 4 weeks after challenge. Lung lesion score was similar in the immunized groups, and lower than that observed in the control. SBA-15-adjuvanted oral vaccine provided immunological response, decreased shedding of M. hyopneumoniae and led to mucosal protection confirmed by the reduced pulmonary lesions. This study provides useful data for future development of vaccines against M. hyopneumoniae.

Improving Mycoplasma hyopneumoniae diagnostic capabilities by harnessing the infection dynamics

Mycoplasma hyopneumoniae remains one of the most problematic bacterial pathogens for pig production. Despite an abundance of observational and laboratory testing capabilities for this organism, diagnostic interpretation of test results can be challenging and ambiguous. This is partly explained by the chronic nature of M. hyopneumoniae infection and its tropism for lower respiratory tract epithelium, which affects diagnostic sensitivities associated with sampling location and stage of infection. A thorough knowledge of the available tools for routine M. hyopneumoniae diagnostic testing, together with a detailed understanding of infection dynamics, are essential for optimizing sampling strategies and providing confidence in the diagnostic process. This study reviewed known information on sampling and diagnostic tools for M. hyopneumoniae and summarized literature reports of the dynamics of key infection outcomes, including clinical signs, lung lesions, pathogen detection, and humoral immune responses. Such knowledge could facilitate better understanding of the performance of different diagnostic approaches at various stages of infection.

Development of ELISA Using Recombinant Proteins for the Diagnosis of Mycoplasma hyopneumoniae Infection

In order to develop a more sensitive and reliable method for detection of serum antibodies against Mycoplasma hyopneumoniae infection in pigs, six recombinant proteins of M. hyopneumoniae (P102, P95, P46, P97 like, Lppt, and hypothetical P987) were used for the standardization of an indirect enzyme-linked immunosorbent assay (ELISA). The proteins were evaluated against 50 sera of the specific pathogen-free and 50 sera of pigs with lesions suggestive of infection. The sensitivity was 88%, 86%, 78%, 74%, 66%, and 60% for the proteins P102, P95, P46, P97 like, Lppt, and hypothetical protein P987, respectively. Moreover, the proteins were used to establish the seroprevalence in two different commercial herds (254 sera pigs from farm considered free of M. hyopneumoniae and 246 from farm with clinical signs of enzootic pneumonia and positive serology for M. hyopneumoniae) and the positive rate was 65.2% for P95, 54.6% for P102, 40.2% for P46, 37.2% for P97 like, 17.4% for the hypothetical P987, and 14% for Lppt protein. In addition, the ELISA with six recombinant proteins was compared to commercial HerdCheck kit using 118 random pig sera samples and the results showed that ELISA with recombinant proteins were more sensitive than the commercial test. These data show that the recombinant proteins P95 and P102 are potential targets to be used in diagnostic tests to detect antibodies against M. hyopneumoniae. Although more studies are necessary, this study provides insights that these recombinant proteins can be useful in epidemiological investigations and as potential biomarkers in differentiating infected animals from those vaccinated.

Effect of antibiotic treatment on Mycoplasma hyopneumoniae detection and infectious potential

Mycoplasma hyopneumoniae (M. hyopneumoniae) causes significant economic losses in the swine industry. Antibiotics with activity against Mycoplasma spp. are employed for disease mitigation and pathogen elimination. However, veterinarians are often challenged with the detection of M. hyopneumoniae by PCR after antibiotic treatment, thus raising the question whether the bacterium is still infectious. The objective of this study was to evaluate the effect of tulathromycin treatment on M. hyopneumoniae detection and infectious potential during the acute and chronic phases of infection. For each infection phase, one age-matched naïve gilt was placed in contact with one M. hyopneumoniae infected gilt that was either treated with tulathromycin, treated and vaccinated, or non-treated, for 14 days. Four replicates per treatment group were performed for each infection phase. A numerical reduction in relative bacterial load was observed in acutely treated gilts compared to non-treated gilts. The rate at which naïve gilts became infected with M. hyopneumoniae was numerically reduced when co-housed with treated, acutely infected gilts compared to those housed with non-treated, infected gilts. During the chronic infection phase, M. hyopneumoniae was detected by PCR in more than 50 % of treated infected gilts and persisted for up to three months post-treatment. Transmission was not detected in all treatment groups however, the possibility that the pathogen was infectious could not be completely ruled out. Further research focused on assessing M. hyopneumoniae detection and viability post-treatment is necessary to guide control and elimination efforts.

Pathogenicity & virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae: is the etiological agent of porcine enzootic pneumonia (EP), a disease that impacts the swine industry worldwide. Pathogen-induced damage, as well as the elicited host-response, contribute to disease. Here, we provide an overview of EP epidemiology, control and prevention, and a more in-depth review of M. hyopneumoniae pathogenicity determinants, highlighting some molecular mechanisms of pathogen-host interactions relevant for pathogenesis. Based on recent functional, immunological, and comparative “omics” results, we discuss the roles of many known or putative M. hyopneumoniae virulence factors, along with host molecules involved in EP. Moreover, the known molecular bases of pathogenicity mechanisms, including M. hyopneumoniae adhesion to host respiratory epithelium, protein secretion, cell damage, host microbicidal response and its modulation, and maintenance of M. hyopneumoniae homeostasis during infection are described. Recent findings regarding M. hyopneumoniae pathogenicity determinants also contribute to the development of novel diagnostic tests, vaccines, and treatments for EP.

Transfer of Mycoplasma hyopneumoniae-specific cell mediated immunity to neonatal piglets

Mycoplasma hyopneumoniae is the primary agent of enzootic pneumonia in pigs. Although cell mediated immunity (CMI) may play a role in protection against M. hyopneumoniae, its transfer from sows to their offspring is poorly characterized. Therefore, maternally-derived CMI was studied in piglets from vaccinated and non-vaccinated sows. The potential influence of cross-fostering before colostrum ingestion on the transfer of CMI from dam to piglets was also investigated. Six M. hyopneumoniae vaccinated sows from an endemically infected herd and 47 of their piglets, of which 24 piglets were cross-fostered, were included, as well as three non-vaccinated control sows from an M. hyopneumoniae-free herd and 24 of their piglets. Vaccinated sows received a commercial bacterin intramuscularly at 6 and 3 weeks prior to farrowing. The TNF-α, IFN-γ and IL-17A production by different T-cell subsets in blood of sows, colostrum and blood of piglets was assessed using a recall assay. In blood of sows cytokine producing T-cells were increased upon M. hyopneumoniae vaccination. Similarly, M. hyopneumoniae-specific T-cells were detected in blood of 2-day-old piglets born from these vaccinated sows. In contrast, no M. hyopneumoniae-specific cytokine producing T-cells were found in blood of piglets from control sows. No difference was found in M. hyopneumoniae-specific CMI between cross-fostered and non-cross-fostered piglets. In conclusion, different M. hyopneumoniae-specific T-cell subsets are transferred from the sow to the offspring. Further studies are required to investigate the role of these transferred cells on immune responses in piglets and their potential protective effect against M. hyopneumoniae infections.

Evaluation of colonization, variable lipoprotein-based serological response, and cellular immune response of Mycoplasma hyorhinis in experimentally infected swine

Mycoplasma hyorhinis (Mhr) is a commensal of the upper respiratory tract that can be shed by nasal secretions and transmitted by direct contact in neonatal and nursery pigs. Lesions associated with Mhr infection include polyserositis and arthritis; however, systemic Mhr disease pathogenesis is not well characterized. This study aimed to investigate the immunopathogenesis and bacterial dissemination pattern of Mhr using single and multiple inoculation approaches in a caesarian-derived colostrum-deprived (CDCD) pig model. Animals in three treatment groups were inoculated once (Mhr 1; n = 12) or four (Mhr 2; n = 8) times with Mhr or sham-inoculated (NC group; n = 3) nasally and by tonsillar painting. Inoculum consisted of a triple cloned Mhr field isolate (4.5 × 10⁷ CFU/mL) in Friis medium. Clinical signs were evaluated daily during the study. Serum and oral fluid antibody (IgA and IgG) response and cellular immune response were assessed using a recombinant chimeric VlpA-G-based indirect ELISA and by ELISpot, respectively. The presence of Mhr in oral fluids, nasal and oropharyngeal swabs were evaluated by qPCR. At 6 wpi, pigs were euthanized and evaluated for gross lesions consistent with Mhr and bacterial colonization in tonsils by qPCR. No clinical signs or gross lesions consistent with Mhr-associated disease were observed throughout the study. For Mhr 2 group, the presence of IgA and IgG in serum and oral fluids were detected at 2 and 4 weeks post-inoculation (wpi), respectively, while in Mhr 1, only IgA was detected in oral fluids at 6 wpi. The proportion of animals shedding Mhr in nasal secretions varied from 20 to 40 % in the Mhr 1 and 62.5-100% in the Mhr 2 group. However, the proportion of animals shedding Mhr in oropharyngeal swabs was consistent through the study (60 %) in Mhr 1 and fluctuated from 20 % to 87.5 % in Mhr 2 group. The lack of clinical signs and the presence of Mhr specific humoral response and bacterial colonization indicates that the multiple inoculation experimental model may mimic subclinical natural infection in the field. In addition, the humoral and transient cellular response did not result in bacterial clearance. Based on these results, animals would have to be exposed multiple times to mount a detectable immune response.

Mycoplasma hyopneumoniae in free-living wild boars in Paraná, Brazil

This is the first study conducted in Paraná, Brazil, to investigate Mycoplasma hyopneumoniae (Mhyo) infection in free-living wild boars. Eighty-eight wild boars were managed by authorized controllers between 2017 and 2019 in the state of Paraná in southern Brazil. Management georeferencing, sex, and weight were recorded for each animal. The presence of Mhyo antibodies in wild boar serum samples was evaluated using a commercial indirect ELISA kit. The presence of enzootic pneumonia-like gross lesions was evaluated, and the observed macroscopic lesions were subjected to immunohistochemistry (IHC). The Chi-square test and the intensity of the association with the odds ratio and 95% confidence interval were used to evaluate the differences in the qualitative variables between groups (sex and municipality). Juvenile wild boars exhibited a higher seroprevalence than older ones (p = 0.005). The Teixeira Soares municipality differed in Mhyo seroprevalence in comparison with Castro (p < 0.001), Ponta Grossa (p = 0.004), and Carambeí (p < 0.001). Females were 6.79 times more likely to present consolidation lesions than males (p = 0.004). Among the evaluated lung samples with injuries, 57.1% (8/14) and 53.8% (7/13) were Mhyo positive by IHC in Castro and Ponta Grossa, respectively, confirming that the identified macroscopic lesions were caused by Mhyo. This study demonstrates the circulation of Mhyo in free-living wild boars, which raises concerns regarding the epidemiological role of this animal species for the spread of the pathogen.

Effect of multiple vaccinations on transmission and degree of Mycoplasma hyopneumoniae infection in gilts

Mycoplasma hyopneumoniae (M. hyopneumoniae) infections continue to result in significant respiratory challenges in the swine industry worldwide. Vaccination for M. hyopneumoniae is commonly utilized, as reduction in bacterial loads and clinical severity in vaccinated pigs have been shown. However, the effect of M. hyopneumoniae vaccination on transmission across different pig populations has been minimally investigated. The aim of this pilot study was to evaluate the effect of multiple vaccinations on M. hyopneumoniae infection, transmission, and genetic variability in infected and susceptible gilt populations. Thirty-two naïve gilts were allocated to four treatment groups: (1) Vaccinated seeder (VS); (2) Non-vaccinated seeder (NVS); (3) Vaccinated contact (VC); and (4) Non-vaccinated contact (NVC). At 5, 7, and 9 weeks of age, all gilts selected to be vaccinated received a commercial M. hyopneumoniae bacterin for a total of 3 doses. At 11 weeks of age, VS and NVS gilts were inoculated with M. hyopneumoniae to become seeders. At 28 days post-inoculation (dpi), VS and NVS gilts were individually relocated to clean experimental rooms, where they were placed in contact with one age-matched VC or NVC gilt (1:1 ratio) for 14 days. Blood and tracheal samples, bronchial swabs, and lung lesions were collected and/or evaluated for M. hyopneumoniae infection. In this study, a three-dose vaccination strategy against M. hyopneumoniae significantly reduced bacterial load in seeder gilts. Furthermore, a numerical reduction in M. hyopneumoniae lung lesions at 28 dpi was observed in VS gilts. All VC gilts in the VS:VC treatment group pairing remained M. hyopneumoniae negative, compared to other groups in which 1-2 transmission events occurred per treatment group. Results from this investigation provide insight on the potential impact of multiple vaccinations on reducing M. hyopneumoniae transmission and infection. Further research encompassing vaccinations of gilt groups in field settings is necessary to validate findings.

Natural transmission and detection of Mycoplasma hyopneumoniae in a naïve gilt population

Mycoplasma hyopneumoniae (M. hyopneumoniae) continues to be a prevalent and economically important swine respiratory pathogen. For M. hyopneumoniae surveillance, blood samples and/or oral fluids are commonly collected from incoming replacement gilts prior to entering sow farms. However, limitations to this approach exist, particularly due to low sensitivity during acute stages of natural infection, leading to diagnostic uncertainty. Therefore, the objective of this study was to evaluate the natural transmission and detection of M. hyopneumoniae based on the introduction of one infected gilt to a naïve population. Twenty-nine naïve gilts were housed with one M. hyopneumoniae naturally exposed gilt for 8 weeks. Deep tracheal catheters, laryngeal swabs, and blood samples were individually collected from each gilt at 0, 1, 2, 4, 6, and 8 weeks post-contact (wpc), along with one pen-based oral fluid sample. Blood samples were assayed by ELISA, while all other samples were tested by real-time PCR. The transmission rate of M. hyopneumoniae (ꞵ) was estimated using a Bayesian mixed-effects generalized linear model. At 8 wpc, 27 % (8/29) of the naïve gilts had become infected (ꞵ = 0.73 new infected gilts/gilt-week). Seroconversion was detected in 3% of contact gilts at 8 wpc. Oral fluids were negative for M. hyopneumoniae at all samplings. In this study, the natural transmission of M. hyopneumoniae was slow and detection varied based on sample type and timing. Thus, M. hyopneumoniae surveillance protocols should include lower respiratory tract samples that are tested by real-time PCR to avoid the introduction of potentially infected gilts into naïve sow farms.

Efficacy in pigs of a new inactivated vaccine combining porcine circovirus type 2 and Mycoplasma hyorhinis

Coinfection with porcine circovirus type 2 (PCV2) and Mycoplasma hyorhinis (Mhr) can induce more-severe disease than a single infection with either. We evaluated the efficacy of a new vaccine combining inactivated PCV2 and Mhr, in a model of PCV2 and Mhr infection. Twenty-five 35-day-old PCV2- and Mhr-free pigs were randomly divided into five groups, with five pigs in each group. The pigs in groups 1 and 2 were vaccinated with the combined vaccine and then challenged with Mhr or PCV2, respectively. The pigs in groups 3 and 4 were not vaccinated and then challenged with PCV2 or Mhr, respectively, and group 5 was used as the unvaccinated unchallenged control. Two weeks after booster immunization via the intramuscular route, all the pigs except those in control group 5 were challenged with PCV2 or Mhr. All the pigs were euthanized 28 days after challenge. The pigs in vaccinated groups 1 and 2 showed a significant increase in weight after challenge with PCV2 or Mhr (P < 0.001), with an average daily gain (ADG) of 0.315 kg compared with unvaccinated groups 3 and 4 (0.279 kg). Mhr was isolated from the unvaccinated pig lungs after Mhr challenge, whereas it was not isolated from the vaccinated pigs. No PCV2 or Mhr was detected with PCR or histochemical staining in vaccinated groups 1 and 2. A statistical analysis showed that the PCV2 and Mhr combined vaccine providing protected against PCV2 infection causing viremia and inguinal lymphadenopathy (5 pigs protected out 5) or against Mhr infection causing fiber inflammation (4 pigs out 5). Thus, we have developed an effective combined vaccine for the prevention and control of PCV2 or Mhr infections in swine herds, this will help reduce prevalence of PCV2 and Mhr coinfections.

Toll-Like Receptor 2 (TLR2) and TLR4 Mediate the IgA Immune Response Induced by Mycoplasma hyopneumoniae

IgA plays an important role in mucosal immunity against infectious pathogens; however, the molecular mechanism of IgA secretion in response to infection remains largely unknown, particularly in Mycoplasma spp. In this study, we found that the levels of IgA in the peripheral blood serum, bronchoalveolar lavage fluid, nasal mucosa, trachea, hilar lymph nodes, and lung tissues of pigs increased significantly after infection with Mycoplasma hyopneumoniae.

IgA plays an important role in mucosal immunity against infectious pathogens; however, the molecular mechanism of IgA secretion in response to infection remains largely unknown, particularly in Mycoplasma spp. In this study, we found that the levels of IgA in the peripheral blood serum, bronchoalveolar lavage fluid, nasal mucosa, trachea, hilar lymph nodes, and lung tissues of pigs increased significantly after infection with Mycoplasma hyopneumoniae. Furthermore, IgA and CD11c were detected in the lungs and hilar lymph nodes by immunohistochemical analysis, and colocalization of these two markers indicates that CD11c⁺ cells play an important role in IgA mucosal immunity induced by M. hyopneumoniae. To investigate the regulatory mechanism of IgA, we separated mouse dendritic cells (DCs) from different tissues and mouse macrophages from the lungs and then cultured mouse B cells together with either DCs or macrophages in vitro. In the mouse lung-DC/B (LDC/B) cell coculture, IgA secretion was increased significantly after the addition of whole-cell lysates of M. hyopneumoniae. The expression of both Toll-like receptor 2 (TLR2) and TLR4 was also upregulated, as determined by mRNA and protein expression analyses, whereas no obvious change in the expression of TLR3 and TLR7 was detected. Moreover, the IgA level decreased to the same as the control group when TLR2 or TLR4 was inhibited instead of TLR8 or TLR7/9. In conclusion, M. hyopneumoniae can stimulate the response of IgA through TLR2 and TLR4 in a mouse LDC/B cell coculture model, and the coculture model is an ideal tool for studying the IgA response mechanism, particularly that with Mycoplasma spp.

Comparison of the sensitivity of laryngeal swabs and deep tracheal catheters for detection of Mycoplasma hyopneumoniae in experimentally and naturally infected pigs early and late after infection

Detection of Mycoplasma hyopneumoniae infection in live pigs is a critical component to measure the success of disease control or elimination strategies. However, in vivo diagnosis of M. hyopneumoniae is difficult and the imperfect sensitivity of diagnostic tools has been deemed as one of the main challenges. Here, the sensitivity of laryngeal swabs and deep tracheal catheters for detection of M. hyopneumoniae early and late after infection was determined using inoculation status as a gold standard in experimentally infected pigs and a Bayesian approach in naturally infected pigs. Three-hundred and twenty 8-week old seeder pigs were intra-tracheally inoculated with M. hyopneumoniae strain 232 and immediately placed with 1920 contact pigs to achieve a 1:6 seeder-to-contact ratio. A subset of seeders and contacts were longitudinally sampled at 7, 28, 97, and 113 days post-inoculation (dpi) and at 28, 56, 84, and 113 days post-exposure (dpe), respectively, using laryngeal swabs and deep tracheal catheters. Samples were tested for M. hyopneumoniae by a species-specific real-time PCR. The sensitivity of deep tracheal catheters was higher than the one obtained in laryngeal swabs at all samplings (seeders: 36% higher than laryngeal swabs at 7 dpi, 29% higher at 97 dpi, and 44% higher at 113 dpi; contacts: 51% higher at 56 dpe, 42% higher at 84 dpe, and 32% higher at 113 dpe). Our study indicates that deep tracheal catheters were a more sensitive sample than laryngeal swabs. The sensitivity of both sample types varied over time and by exposure method, and these factors should be considered when designing diagnostic strategies.

Identification of specific B cell linear epitopes of mycoplasma hyorhinis P37 protein using monoclonal antibodies against baculovirus-expressed P37 protein

BACKGROUND

Mycoplasma hyorhinis (Mhr) is the etiologic agent of lameness and polyserositis in swine. P37 is a membrane protein of Mhr that may be an important immunogen and is a potential target for diagnostic development. However, there is little information concerning Mhr P37 protein epitopes. A precise analysis of the P37 protein epitopes should extend our understanding of the antigenic composition of the P37 protein and the humoral immune responses to Mhr infection. Investigating the epitopes of Mhr P37 will help to establish a detection method for Mhr in tissue and provide an effective tool for detecting Mhr infection.

RESULTS

Western blot and indirect immunofluorescence assays (IFA) confirmed that the expressed P37 protein was recognized by Mhr-positive porcine and mouse sera. Furthermore, the P37 protein was purified using affinity chromatography and used to immunize mice for hybridoma cell fusion. Four monoclonal antibodies (mAbs) found to be positive for Mhr were detected in infected lung tissue. A panel of truncated P37 proteins was used to identify the minimal B cell linear epitopes of the protein based on these mAbs. The core epitope was determined to be ²⁰⁶KIKKAWNDKDWNTFRNF²²²_. CONCLUSIONS: In this study, we identified 17 critical amino acids that determine the epitope of the P37 protein of Mhr. This study identified mAbs that could provide useful tools for investigating the Mhr P37 antigenic core epitope (amino acids 206-222) and detecting Mhr-specific antigens in infected tissue.

Early detection and differential serodiagnosis of Mycoplasma hyorhinis and Mycoplasma hyosynoviae infections under experimental conditions

Mycoplasma hyorhinis (MHR) and Mycoplasma hyosynoviae (MHS) are common opportunistic pathogens in the upper respiratory tract and tonsils of swine. The identification of the specific species involved in clinical cases using conventional diagnostic methods is challenging. Therefore, a recombinant chimeric polypeptide based on the seven known variable lipoproteins (A-G) specific of MHR and a cocktail of surface proteins detergent-extracted from MHS cultures were generated and their suitability as antemortem biomarkers for serodiagnosis of MHR- and MHS-infection were evaluated by ELISA. M. hyorhinis and MHS ELISA performance, evaluated using serum samples collected over a 56-day observation period from pigs inoculated with MHR, MHS, M. hyopneumoniae, M. flocculare, or Friis medium, varied by assay, targeted antibody isotype, and cutoffs. The progressions of MHR and MHS clinical diseases were evaluated in relation to the kinetics of the isotype-specific antibody response in serum and bacterial shedding in oral fluids during the observation period. In pigs inoculated with MHR, bacterial DNA was detected in one or more of the 5 pens at all sampling points throughout the study, IgA was first detected at DPI 7, one week before the first clinical signs, with both IgA and IgG detected in all samples collected after DPI 14. The peak of MHS shedding (DPI 8) coincided with the onset of the clinical signs, with both IgA and IgG detected in all serum samples collected ≥ DPI 14. This study demonstrated, under experimental conditions, that both ELISAs were suitable for early detection of specific antibodies against MHR or MHS. The diagnostic performance of the MHR and MHS ELISAs varied depending on the selected cutoff and the antibody isotype evaluated. The high diagnostic and analytical specificity of the ELISAs was particularly remarkable. This study also provides insights into the infection dynamics of MHR-associated disease and MHS-associated arthritis not previously described.

A Porcine circovirus type 2b (PCV2b)-based experimental vaccine is effective in the PCV2b-Mycoplasma hyopneumoniae coinfection pig model

Porcine circovirus type 2 (PCV2) is one of the major swine pathogens causing high economic losses due to PCV2-associated disease (PCVAD). PCV2 infection is not only immunosuppressive by damaging lymphoid tissues but is also exacerbated by co-infections with other pathogens including Mycoplasma hyopneumoniae. While PCV2 can be divided into several genotypes, currently only PCV2a, PCV2b and PCV2d are globally prevalent and considered of major importance. Most commercial PCV2 vaccines are based on PCV2a isolates; however, the high prevalence of PCV2b and PCV2d in the global pig population is raising concerns among pig veterinarians. The objective of this study was to evaluate the efficacy of an experimental PCV2b-based subunit vaccine in a combined PCV2b and M. hyopneumoniae coinfection model. Briefly, a total of 49 PCV2- and M. hyopneumoniae-free 3-week-old pigs were randomly divided into four groups: A non-vaccinated, non-infected NEG-CONTROL group, a non-vaccinated, PCV2b-infected, POS-CONTROL group, and two vaccinated and PCV2b-infected groups (SINGLE-VAC, DUAL-VAC). SINGLE-VAC and DUAL-VAC pigs were vaccinated at 3 weeks of age and DUAL-VAC pigs received a booster dose at 5 weeks of age. All pigs, except NEG-CONTROLs, were experimentally infected with M. hyopneumoniae 28 days after initial vaccination and challenged with PCV2b one week later. The pigs were necropsied 21 days after PCV2b challenge. Prior to PCV2b challenge, both vaccinated groups had detectable humoral and cell-medicated immune responses to PCV2. Vaccination significantly reduced PCV2b viremia and also reduced or eliminated PCV2-associated lymphoid lesions compared to the POS-CONTROL pigs. Under the study conditions, an experimental PCV2b vaccine protected conventional growing pigs against PCV2b viremia and associated lesions in a coinfection model with some advantages of the two-dose regimen versus the one dose regimen. Both protocols induced neutralizing antibodies against PCV2a and PCV2d prior to challenge.

Temporal patterns of colonization and infection with Mycoplasma hyorhinis in two swine production systems in the USA

Control of Mycoplasma hyorhinis (M. hyorhinis) associated disease is currently hindered by limited knowledge of the epidemiology and ecology of this organism. A prospective longitudinal investigation was conducted to determine the dynamics of M. hyorhinis colonization in two swine production systems. In each system (A, B), 51 young sows (parities 1, 2) and 56 older sows (>parity 2) were selected at farrowing and tested by qPCR of nasal swabs and for antibodies by serum ELISA. From each sow, a piglet was randomly selected, and nasal and serum samples were collected at birth, weaning, and 10 days post-weaning. Two further samplings were performed in the nursery and finishing stages during the high-risk periods for M. hyorhinis-associated disease, and 12 pigs were euthanized and necropsied at these later sampling events. The prevalence of M. hyorhinis colonization in sows was low (<5%). No associations were found between sow parity or sow serum titer and piglet nasal colonization at either birth or weaning. In contrast to the low prevalence (0.95-2.70%) observed in piglets pre-weaning, most pigs became colonized during the first four weeks after weaning and remained positive throughout the nursery and finishing stages. The detection of M. hyorhinis in oral fluids followed similar patterns as those observed using nasal swabs. ELISA results showed decreased detection of maternal antibodies at around 3 weeks of age and a subsequent increase after natural exposure. The role of M. hyorhinis in polyserositis and arthritis was demonstrated in these two herds. Establishing the temporal dynamics of exposure and infection with M. hyorhinis in pigs will enable more strategic implementation of intervention strategies in affected herds.

Analysis of swine antigen-specific antibody responses to Mycoplasma hyopneumoniae infection determined by protein microarray

Pigs harbor several different species of mycoplasmas, of which Mycoplasma hyopneumoniae presents the most significant economic impact on the swine industry. While ELISAs are the predominant diagnostic assay to measure antibody responses during infection with M. hyopneumoniae, the assay itself is only a rough estimate of the total antibody response. It lends little information on pathogen-wide antigen-specific responses. In addition, antibody responses to M. hyopneumoniae as measured by ELISA are slow to develop in infected swine. Our goal was to determine if a protein microarray could be more sensitive and informative of the serological responses of pigs to M. hyopneumoniae infection. The gene sequences of approximately 50 M. hyopneumoniae surface proteins or protein fragments were cloned, mutated to remove UGA codons, expressed in Escherichia coli and purified. The arrays were used to interrogate pig sera from various sources. Sera from naturally-infected swine gave some variability in antigen-specific responses, but, unexpectedly, the responses against the C-terminal portion of the major adhesin P97 was weak in all animals, including those that were experimentally infected. In two of four 118-day experimentally-infected caesarian-derived colostrum-deprived pigs, the strongest antibody responses occurred on days 30 and 54 against members of the P97/P102 paralog families. Our Day 0 results in the other two animals indicate that although thought to be mycoplasma free by all known criteria (serology and PCR), they may have harbored an inapparent Mycoplasma infection. In summary, the protein microarray has the potential to identify new targets for assay development to enhance sensitivity of antibody-based assays.

A p37-based ELISA used to monitor anti- Mycoplasma hyorhinis IgG in serum from pigs immunized with inactivated M. hyorhinis vaccines

Mycoplasma hyorhinis is an important pathogen of swine that can often occur as a respiratory coinfection with viral pathogens, but can also cause arthritis and polyserositis in infected animals. To date, no assay is available to assess the serologic response to M. hyorhinis vaccines, to our knowledge. We used recombinantly expressed M. hyorhinis p37 protein to monitor the magnitude of the IgG response in vaccinated animals. The assay was able to distinguish animals vaccinated with M. hyorhinis from those vaccinated with the other important Mycoplasma species: M. hyopneumoniae and M. hyosynoviae. When formulated with an ideal adjuvant, inactivated vaccines designed to protect animals against M. hyorhinis induced a measurable and dose-dependent antibody response against the p37 protein. Additionally, the protein appears to be highly conserved between strains of M. hyorhinis isolated in the United States. The specificity of the assay as well as the conservation and immunogenicity of the p37 protein make it an ideal candidate antigen for use in measuring the immune response against M. hyorhinis after vaccination in weaned pigs.

Detection and phylogenetic analysis of Mycoplasma hyopneumoniae from Tibetan pigs in western China

Enzootic pneumonia (EP), often caused by Mycoplasma hyopneumoniae, occurs in Tibetan pigs between October and December in Western China. The aim of this study was to determine the prevalence of M. hyopneumoniae in Tibetan pig herds and also the prevalence of infection. M. hyopneumoniae was detected using enzyme-linked immunosorbent assay, polymerase chain reaction (PCR), and 16S rRNA sequencing. Twenty-nine inflammatory gross-lesions were observed in 155 lungs of slaughtered pigs. Invasion of focal lymphocytes was confirmed by paraffin sectioning and hematoxylin-eosin staining of lung sections. Bronchoalveolar lavage fluid (BALF) from slaughtered Tibetan pigs and nasal swabs from others were assayed using PCR. The prevalence of M. hyopneumoniae in Tibetan pig herds (via ELISA) was 20.48% (93/454) in 3 provinces (Sichuan, Tibet autonomous region, and Qinghai) between October and December of 2014. The difference in prevalence among animals in six different growing stages was statistically significant (P < 0.05). Anti-M. hyopneumoniae antibody was detected in breeding sows (45.83%; 22/48) and piglets (50%; 3/6). PCR and gel electrophoresis of BALF showed that 6.45% (10/155) of pigs were positive for M. hyopneumoniae. The presence of M. hyopneumoniae in serum was higher in piglets and breeding sows than in any other group. In conclusion, the results of this study showed that M. hyopneumoniae is prevalent among Tibetan pigs between October and December in Western China. To the authors' knowledge, this is the first investigation of M. hyopneumoniae prevalence in Tibetan pigs of Western China using serological tests, PCR, and 16S rRNA sequencing.

Microbiome overview in swine lungs

Mycoplasma hyopneumoniae is the etiologic agent of swine enzootic pneumonia. However other mycoplasma species and secondary bacteria are found as inhabitants of the swine respiratory tract, which can be also related to disease. In the present study we have performed a total DNA metagenomic analysis from the lungs of pigs kept in a field condition, with suggestive signals of enzootic pneumonia and without any infection signals to evaluate the bacteria variability of the lungs microbiota. Libraries from metagenomic DNA were prepared and sequenced using total DNA shotgun metagenomic pyrosequencing. The metagenomic distribution showed a great abundance of bacteria. The most common microbial families identified from pneumonic swine's lungs were Mycoplasmataceae, Flavobacteriaceae and Pasteurellaceae, whereas in the carrier swine's lungs the most common families were Mycoplasmataceae, Bradyrhizobiaceae and Flavobacteriaceae. Analysis of community composition in both samples confirmed the high prevalence of M. hyopneumoniae. Moreover, the carrier lungs had more diverse family population, which should be related to the lungs normal flora. In summary, we provide a wide view of the bacterial population from lungs with signals of enzootic pneumonia and lungs without signals of enzootic pneumonia in a field situation. These bacteria patterns provide information that may be important for the establishment of disease control measures and to give insights for further studies.

Two clinical isolates of Mycoplasma hyosynoviae showed differing pattern of lameness and pathogen detection in experimentally challenged pigs

Mycoplasma (M.) hyosynoviae is known to colonize and cause disease in growing-finishing pigs. In this study, two clinical isolates of M. hyosynoviae were compared by inoculating cesarean-derived colostrum-deprived and specific-pathogen-free growing pigs. After intranasal or intravenous inoculation, the proportion and distribution pattern of clinical cases was compared in addition to the severity of lameness. Tonsils were found to be the primary site of colonization, while bacteremia was rarely detected prior to the observation of clinical signs. Regardless of the clinical isolate, route of inoculation, or volume of inocula, histopathological alterations and tissue invasion were detected in multiple joints, indicating an apparent lack of specific joint tropism. Acute disease was primarily observed 7 to 10 days post-inoculation. The variability in the severity of synovial microscopic lesions and pathogen detection in joint cavities suggests that the duration of joint infection may influence the diagnostic accuracy. In summary, these findings demonstrate that diagnosis of M. hyosynoviae-associated arthritis can be influenced by the clinical isolate, and provides a study platform to investigate the colonization and virulence potential of field isolates. This approach can be particularly relevant to auxiliate in surveillance and testing of therapeutic and/or vaccine candidates.

Mycoplasma hyorhinis is a potential pathogen of porcine respiratory disease complex that aggravates pneumonia caused by porcine reproductive and respiratory syndrome virus

The porcine respiratory disease complex (PRDC) caused by numerous bacterial and viral agents has a great impact on pig industry worldwide. Although Mycoplasma hyorhinis (Mhr) has been frequently isolated from lung lesions from pigs with PRDC, the pathological importance of Mhr may have been underestimated. In this study, 383 serum samples obtained from seven herds with a history of PRDC were tested for specific antibodies to Mhr, Mycoplasma hyopneumoniae (Mhp), and porcine reproductive and respiratory syndrome virus (PRRSV). Seropositive rates of PRRSV were significantly correlated with those of Mhr (correlation coefficient, 0.862; P-value, 0.013), but not with those of Mhp (correlation coefficient, -0.555; P-value, 0.196). In vivo experiments demonstrated that pigs co-infected with Mhr and PRRSV induced more severe lung lesions than pigs infected with Mhr or PRRSV alone. These findings suggest that Mhr is closely associated with pneumonia caused by PRRSV and provide important information on Mhr pathogenesis within PRDC. Therefore, effective PRDC control strategies should also consider the potential impact of Mhr in the pathogenesis of PRDC.

Dynamics of Mycoplasma hyopneumoniae seroconversion and infection in pigs in the three main production systems

In this study, we investigated the dynamics of Mycoplasma hyopneumoniae infections in 66 pig farms, with different production systems (one-, two-, and three-site systems), and considered different risk factors. Serological assay was used to detect serum antibodies against M. hyopneumoniae and real time polymerase chain reaction (RT-PCR) was performed to detect M. hyopneumoniae DNA in tracheobronchial swabs. Results demonstrated that M. hyopneumoniae infection status was predominantly influenced by the age of the animals and the type of production system. Infection rates were higher in older animals and the prevalence was higher in the one- and two-site systems than in the three-site systems. Dynamics of infection by RT-PCR showed that earlier M. hyopneumoniae infection on one-site farms occurs earlier, while on two- and three-site farms occurs later but spreads faster, suggesting that contact between animals of different age favors the transmission.

Quantitative real-time polymerase chain reaction for detecting Mycoplasma hyosynoviae and Mycoplasma hyorhinis in pen-based oral, tonsillar, and nasal fluids

Mycoplasma (M.) hyorhinis and M. hyosynoviae are pathogens known to cause disease in pigs post-weaning. Due to their fastidious nature, there is increased need for culture-independent diagnostic platforms to detect these microorganisms. Therefore, this study was performed to develop and optimize quantitative real-time PCR (qPCR) assays to rapidly detect M. hyorhinis and M. hyosynoviae in pen-based oral fluids as well as nasal and tonsillar fluids as proxies for samples used in swine herd surveillance. Two methods of genomic DNA extraction, automated versus manual, were used to compare diagnostic test performance. A wean-to-finish longitudinal study was also carried out to demonstrate the reproducibility of using pen-based oral fluids. Overall, pen-based oral and tonsillar fluids were more likely to be positive for both types of bacteria whereas only M. hyorhinis was detected in nasal fluids. DNA extraction protocols were shown to significantly influence test result. Although the initial detection time somewhat differed, both organisms were repeatedly detected in the longitudinal study. Overall, this study evaluated two qPCR methods for rapid and specific detection of either mycoplasma. Results from the present investigation can serve as a foundation for future studies to determine the prevalence of the two microorganisms, environmental load, and effectiveness of veterinary interventions for infection control.