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

Characterization of a Mycoplasma hyopneumoniae aerosol infection model in pigs

The purpose of the present study was to develop and characterize an experimental aerosol model for Mycoplasma hyopneumoniae (M. hyopneumoniae) infection and respiratory disease in pigs. The experiment was carried out to determine the pathogenicity, colonization, mucosal immune response, and clinical course of disease of dose-controlled aerosols of M. hyopneumoniae. Four groups of three M. hyopneumoniae-free gilts each were individually exposed to aerosols of diluted lung homogenate containing M. hyopneumoniae strain 232 in a chamber. Each group was exposed to different doses of viable organisms (105 to 106 color changing units/mL during 15-20 or 30-35 min in two consecutive days). Nasal, laryngeal, and deep-tracheal secretions were collected from each gilt at 0, 7, 14, 21, and 28 days post-exposure (dpe). Blood samples were collected at 0 and 28 dpe. At necropsy, lung lesions were assessed, and bronchial secretions and bronchoalveolar lavage fluid (BALF) were collected from each lung set. Blood was used to assess seroconversion by means of an indirect ELISA, while BALF, deep-tracheal and nasal secretions were tested by modifying the ELISA to evaluate mucosal IgG and IgA production. Nasal, laryngeal, deep-tracheal, and bronchial secretions were tested by real-time PCR to evaluate bacterial load. Gilts became infected irrespective of the infectious dose, as determined by M. hyopneumoniae detection in deep-tracheal secretions from all gilts at 7 dpe. A specific local humoral immune response starting at 14 dpe was detected in all gilts. While all experimental groups presented gilts with some extent of mycoplasmal pneumonia, only the exposure of gilts to high-dose aerosols consistently reproduced typical clinical signs and severe lung lesions. These results showed that the reproduction of mycoplasmal pneumonia by means of infectious aerosols can be successfully achieved at experimental level, making this model a valuable alternative to evaluate preventive and treatment measures against M. hyopneumoniae.

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.

A diagnostic approach to confirm Mycoplasma hyopneumoniae "Day zero" for pathogen eradication

Breeding herds in the US are trending toward eradication of Mycoplasma hyopneumoniae (M. hyopneumoniae) due to the positive impact on welfare and downstream production. In an eradication program, "Day 0″ is the time point when the last replacement gilts to enter the herd were exposed to M. hyopneumoniae and marks the beginning of a herd closure. However, no specific diagnostic protocols are available for confirmation of successful exposure to define Day 0. Therefore, the objective of this study was to develop diagnostic guidelines, including sample collection approaches, for two common gilt exposure methods to confirm an entire population has been infected with M. hyopneumoniae following purposeful exposure. Forty gilts, age 21-56 days, were ear-tagged for longitudinal sample collection at five commercial gilt developer units (GDUs) and were exposed to M. hyopneumoniae by natural contact or aerosolization. Study gilts originated from sources known to be negative to major swine pathogens, including M. hyopneumoniae, and were sampled prior to exposure to confirm negative status, then every two weeks. Blood samples were collected for antibody detection, while laryngeal and deep tracheal secretions and pen based oral fluids were collected for PCR, and sampling continued until at least 85% of samples were positive by PCR. Detection of M. hyopneumoniae varied greatly based on sample type. Oral fluids showed the lowest detection in groups of gilts detected positive by other sample types. Detection by PCR in deep tracheal secretions was higher than in laryngeal secretions. Seroconversion to and PCR detection of M. hyopneumoniae on oral fluids were delayed compared to PCR detection at the individual level. By two weeks post-exposure, at least 85% of study gilts in three GDUs exposed by aerosolization were PCR positive in deep tracheal secretions. Natural contact exposure resulted in 22.5% of study gilts becoming PCR positive by two weeks post-initial exposure, 61.5% at four weeks, and 100% at six weeks on deep tracheal secretions. Deep tracheal secretions required the lowest number of gilts to sample for the earliest detection compared to all other samples evaluated. As observed in one of the GDUs using aerosolization, demonstration of failure to expose gilts to M. hyopneumoniae allowed for early intervention in the exposure protocol and delay of Day 0, for accurate timing of the eradication protocol. Sampling guidelines proposed in this study can be used for verification of M. hyopneumoniae infection of gilts following exposure to determine Day 0 of herd closure.

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.

Cough associated with the detection of Mycoplasma hyopneumoniae DNA in clinical and environmental specimens under controlled conditions

Background

The association of cough with Mycoplasma hyopneumoniae (MHP) DNA detection in specimens was evaluated under conditions in which the MHP status of inoculated and contact-infected pen mates was closely monitored for 59 days post-inoculation (DPI).

Methods

Seven-week-old pigs (n = 39) were allocated to five rooms (with one pen). Rooms contained 9 pigs each, with 1, 3, 6, or 9 MHP-inoculated pigs, respectively, except Room 5 (three sham-inoculated pigs). Cough data (2 × week) and specimens, tracheal swabs (2 × week), oral fluids (daily), drinker wipes (~ 1 × week), and air samples (3 × week) were collected. At 59 DPI, pigs were euthanized, and lung and trachea were evaluated for gross and microscopic lesions. Predictive cough value to MHP DNA detection in drinker and oral fluid samples were estimated using mixed logistic regression.

Results

Following inoculation, MHP DNA was first detected in tracheal swabs from inoculated pigs (DPI 3), then oral fluids (DPI 8), air samples (DPI 10), and drinker wipes (21 DPI). MHP DNA was detected in oral fluids in 17 of 59 (Room 1) to 43 of 59 (Room 3) samples, drinker wipes in 4 of 8 (Rooms 2 and 3) to 5 of 8 (Rooms 1 and 4) samples, and air samples in 5 of 26 (Room 2) or 3 of 26 (Room 4) samples. Logistic regression showed that the frequency of coughing pigs in a pen was associated with the probability of MHP DNA detection in oral fluids (P < 0.01) and nearly associated with drinker wipes (P = 0.08). Pathology data revealed an association between the period when infection was first detected and the severity of gross lung lesions.

Conclusions

Dry, non-productive coughs suggest the presence of MHP, but laboratory testing and MHP DNA detection is required for confirmation. Based on the data from this study, oral fluids and drinker wipes may provide a convenient alternative for MHP DNA detection at the pen level when cough is present. This information may help practitioners in specimen selection for MHP surveillance.

Cross-sectional study on the in-herd prevalence of Mycoplasma hyopneumoniae at different stages of pig production

BACKGROUND

A cross-sectional study was carried out to assess the prevalence of Mycoplasma hyopneumoniae infections before vaccination in 3-week-old piglets and to gain information about infection dynamics.

METHODS

In 13 German and three Austrian farms with a known history of enzootic pneumonia, 790 piglets and 158 sows were sampled (blood samples, tracheobronchial swabs [TBS] [piglets], laryngeal swabs [LS] [sows]), and 525 pen-based oral fluids (OFs) were collected in growing and fattening pigs. Laboratory diagnostics included enzyme-linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (PCR) analyses.

RESULTS

Antibodies to M. hyopneumoniae were present in 87.5 per cent of all herds. Seroprevalence ranged from 0.0 to 100.0 per cent and 0.0 to 88.0 per cent in sows and piglets, respectively. M. hyopneumoniae-deoxyribonucleic acid (DNA) was present in 3.8 and 0.4 per cent of LS and TBS, respectively. Gilts had a 10.9 times higher chance being M. hyopneumoniae PCR-positive than older sows. In 75.0 per cent of all farms, M. hyopneumoniae-DNA was present in OFs. Detection rate was significantly higher in OFs of 20-week-old than in younger pigs (p < 0.001).

CONCLUSION

Results indicate that M. hyopneumoniae infections of the lower respiratory tract in piglets are rare but highlight the role of gilts in maintaining infection in the herd. Collecting OFs seems promising for surveillance, if coughing occurs simultaneously.

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.