Characterisation of the tracheal transcriptional response of chickens to chronic infection with Mycoplasma synoviae.

Mycoplasma synoviae causes infectious synovitis and respiratory tract infections in chickens and is responsible for significant economic losses in the poultry industry. Effective attachment and colonisation of the trachea is critical for the persistence of the organism and progression of the disease it causes. The respiratory tract infection is usually sub-clinical, but concurrent infection with infectious bronchitis virus (IBV) is known to enhance the pathogenicity of M. synoviae. This study aimed to explore differentially expressed genes in the tracheal mucosa, and their functional categories, during chronic infection with M. synoviae, using a M. synoviae-IBV infection model. The transcriptional profiles of the trachea were assessed 2 weeks after infection using RNA sequencing. In chickens infected with M. synoviae or IBV, only 1 or 8 genes were differentially expressed compared to uninfected chickens, respectively. In contrast, the M. synoviae-IBV infected chickens had 621 upregulated and 206 downregulated genes compared to uninfected chickens. Upregulated genes and their functional categories were suggestive of uncontrolled lymphoid cell proliferation and an ongoing pro-inflammatory response. Genes associated with anti-inflammatory effects, pathogen removal, apoptosis, regulation of the immune response, airway homoeostasis, cell adhesion and tissue regeneration were downregulated. Overall, transcriptional changes in the trachea, 2 weeks after infection with M. synoviae and IBV, indicate immune dysregulation, robust inflammation and a lack of cytotoxic damage during chronic infection. This model provides insights into the pathogenesis of chronic infection with M. synoviae.

Transcriptomic analysis of the effects of tylosin on the protective immunity provided by the Mycoplasma gallisepticum vaccine Vaxsafe MG ts-304.

The antimicrobial tylosin is commonly used to control mycoplasma infections, sometimes in combination with vaccination. However, the efficacy of a live mycoplasma vaccine, when combined with subsequent antimicrobial treatment, against the effects of subsequent infection with a virulent strain is unknown. This study employed differential gene expression analysis to evaluate the effects of tylosin on the protection provided by the live attenuated Vaxsafe MG ts-304 vaccine, which has been shown to be safe and to provide long-term protective immunity against infection with Mycoplasma gallisepticum. The transcriptional profiles of the tracheal mucosa revealed significantly enhanced inflammation, immune cell proliferation and adaptive immune responses in unvaccinated, untreated birds and in unvaccinated birds treated with tylosin 2 weeks after infection with virulent M. gallisepticum. These responses, indicative of the typical immune dysregulation caused by infection with M. gallisepticum, were less severe in the unvaccinated, tylosin-treated birds than in the unvaccinated, untreated birds. This was attributable to the effect of residual levels of tylosin in the tracheal mucosa on replication of virulent M. gallisepticum. These responses were not detected in vaccinated, tylosin-treated birds or in vaccinated, untreated birds after infection. The tracheal mucosal transcriptional profiles of these birds resembled those of unvaccinated, untreated, uninfected birds, suggesting a rapid and protective secondary immune response and effective vaccination. Overall, these results show that, although tylosin treatment reduced the duration of immunity, the initial protective immunity induced by Vaxsafe MG ts-304 lasted for at least 22 weeks after vaccination, even after the administration of tylosin for 16 weeks following vaccination.

Evaluation of the MilA ELISA for the diagnosis of herd infection with Mycoplasma bovis using bulk tank milk and estimation of the prevalence of M. bovis in Australia.

Infection with Mycoplasma bovis has been identified as a growing threat in dairy industries worldwide and there is an urgent need for an inexpensive and accurate herd-level screening tool to identify herds that have been exposed to M. bovis. This study aimed to evaluate the use of the MilA ELISA for testing bulk tank milk (BTM) samples for antibodies against M. bovis and estimate a suitable cut-off and diagnostic sensitivity (DSe) and specificity (DSp) for this assay. An optimal cut-off was then applied for investigating the geographical and seasonal distribution of infection with M. bovis in Australia. A total of 5554 BTM samples from 2683 dairy herds were collected during March, August and December 2017. BTM samples were tested in the MilA ELISA and a cut-off of 29 antibody units (AU) was estimated to be optimal using Bayesian latent class analysis which makes no assumption about the true disease status of herds under investigation. At this cut-off, the DSe and DSp were estimated to be 96.6% (95% highest probability density [HPD] interval: 87.0, 99.8) and 94.2% (95% HPD: 89.9, 97.4), respectively. The diagnostic specifications were found to vary markedly with stage of the production cycle, suggesting that targeted sampling was needed to maximize accuracy. We also found distinct differences in the apparent prevalence of M. bovis in different dairying regions, as well as seasonal variation. The highest apparent prevalence of M. bovis was observed in samples collected in March and an overall drop in the proportion of positive herds was seen from March to December. Overall, this study provides insights into the dynamics of BTM antibodies against M. bovis in Australian dairy herds and how the MilA ELISA can be applied for bulk tank milk testing.