Characterisation, diagnosis and control of Mycoplasma spp. in Australian dairy herds

Abstract

Mycoplasma species can cause severe disease in cattle worldwide. In Australia, there has been an observed increase in the incidence of disease caused by Mycoplasma species in the last nine years. Despite this, little research has been undertaken on mycoplasma infection in Australia and thus the focus of the study described in this thesis was on the characterisation, diagnosis and control of Mycoplasma spp in Australian dairy herds. Whole genome sequencing of 82 Australian Mycoplasma bovis isolates collected over a 9 year period (2006-2015) revealed a seemingly single strain persisting throughout Australia, with marked genomic homology (Chapter 2). When diagnosing bovine samples for the presence of M. bovis, M. californicum and M. bovigenitalium, multiplex PCR was comparable to culture, with the superior method dependent on sample type and the need to identify multiple species per sample (Chapter 3). The use of PCR and culture may also be complemented by the use of an antibody-ELISA (Bio-X Bio K 302, Bio-X Diagnostics, Rochefort, Belgium) on BTM samples, in identifying herds from which the purchase of animals may pose a higher biosecurity risk for introducing M. bovis into non-infected herds (Chapter 4). Lastly, milk acidification was effective at eliminating viable M. bovis and Salmonella Dublin organisms in milk, if the appropriate pH and exposure time was maintained (Chapter 5). While much work is still needed on this debilitating pathogen, the overall findings of this study regarding the genomic characteristics of Australian M. bovis isolates, the timely use of available diagnostic methodologies in analyzing appropriate samples, and the potential control options aimed in particular at manipulating host and environmental (including management) factors provide useful guidelines for managing the serious challenge posed by the emergence of Mycoplasma spp. infection in Australian dairy herds.