Use of serological and mucosal immune responses to Mycoplasma hyopneumoniae antigens P97R1, P46 and P36 in the diagnosis of infection.

Currently available ELISAs used to diagnose Mycoplasma hyopneumoniae infection in pigs have high specificity but low sensitivity. To develop more sensitive assays, the kinetics of specific serum IgG and respiratory mucosal sIgA responses against three M. hyopneumoniae antigens, namely, P97R1 (an adhesin protein), P46 (a membrane protein), and P36 (a cytosolic protein), were characterised over 133 days following experimental infection. Immunoglobulin G against the three proteins remained at high concentrations from 28 to 133 days post-infection (dpi), although IgG against P97R1 was detected earlier and was more reactive than the other two antigens under assessment. Mucosal sIgA appeared earlier than serum IgG but did not persist as long; sIgA concentrations against P97R1 were the highest. Seroconversion was detected 2 weeks earlier with the P97R1-based ELISA than with a commercially available ELISA. On analysis of serum samples from five pig farms that did not use a M. hyopneumoniae vaccine, the P97R1-based IgG ELISA demonstrated a 73.6% coincidence rate with the commercial kit. Moreover, this more specific P97R1-based ELISA detected more positive samples than the commercial kit (52.8% vs. 39.2%). It was concluded that the systemic immune response to M. hyopneumoniae infection in pigs was delayed in onset but persistent whereas the mucosal response developed more rapidly but was less sustained. The P97R1 antigen was identified as a suitable serological marker for diagnosing M. hyopneumoniae infection in pigs, particularly early stage infection.

Development and validation of an attenuated Mycoplasma hyopneumoniae aerosol vaccine.

Mycoplasma hyopneumoniae (M. hyopneumoniae) causes a chronic respiratory disease with high morbidity and low mortality in swine, and has been presented as a major cause of growth retardation in the swine industry. Aerosol vaccination presents a needle free, high throughput, and efficient platform for vaccine delivery, and has been widely applied in poultry vaccination. However, aerosol vaccines have rarely been used in swine vaccination primarily because the long and curving respiratory track of swine presents a barrier for vaccine particle delivery. To develop an effective M. hyopneumoniae aerosol vaccine, three major barriers need to be overcome: to optimize particle size for aerosol delivery, to maintain the viability of mycoplasma cells in the vaccine, and to optimize the environmental conditions for vaccine delivery. In this study, an aerosol mycoplasma vaccine was successfully developed based on a conventional live attenuated M. hyopneumoniae vaccine. Specifically, the Pari LCD nebulizer was used to produce an aerosol vaccine particle size less than 5 µm; and a buffer with 5% glycerol was developed and optimized to prevent inactivation of M. hyopneumoniae caused by aerosolization and evaporation. Before nebulization, the room temperature and relative humidity were control to 20-25 °C and 70-75%, respectively, which helped maintain the viability of aerosol vaccine. Animal experiments demonstrated that this newly developed aerosol vaccine was effectively delivered to swine low respiratory track, being confirmed by nested-PCR, in situ hybridization and scanning electron microscope. Moreover, M. hyopneumoniae specific sIgA secretion was detected in the nasal swab samples at 14 days post-immunization. To our knowledge, this is the first report on a live M. hyopneumoniae aerosol vaccine.

Development and validation of a SIgA-ELISA for the detection of Mycoplasma hyopneumoniae infection.

An alternative indirect enzyme-linked immunosorbent assay (ELISA) for the detection of Mycoplasma hyopneumoniae secretory IgA (SIgA) antibody (SIgA-ELISA) was developed using an adhesin (P97R1) of M. hyopneumoniae produced in Escherichia coli. The SIgA-ELISA assay was validated by the comparison with a nested-PCR assay and a commercial M. hyopneumoniae antibody detection kit (IgG-ELISA). Two hundred and sixty nasal swab samples, bronchoalveolar lavage fluids or serum samples were prepared for SIgA-ELISA validation from a M. hyopneumoniae-free farm, a M. hyopneumoniae vaccinated farm and two M. hyopneumoniae contaminated farms. The results showed that the SIgA-ELISA assay could distinguish the M. hyopneumoniae infection from M. hyopneumoniae vaccinated pigs, which was impossible for the current commercial M. hyopneumoniae antibody detection kits. The diagnostic sensitivity (DSN), specificity (DSP) and accuracy of the SIgA-ELISA were 97.0%, 94.4% and 95.8%, respectively and were compared with nested-PCR on 260 field nasal swab samples. The results of repeatability tests revealed that the coefficients of variation of swab samples within and between runs were less than 10%. This SIgA-ELISA is a needle-free detection methodology for large-scale surveys of M. hyopneumoniae infection.