dMycoplasma bovis is a pathogen of emerging significance in cattle throughout the world that is causing a range of diseases, including mastitis, arthritis, and pneumonia. The limited availability and efficacy of current diagnostic and prophylactic tools for its control and its increasing antimicrobial resistance are contributing to its increasing importance in beef and dairy cattle. We have developed an indirect IgG enzyme-linked immunosorbent assay (ELISA) based on a recombinant fragment of the MilA protein and have shown its potential as an effective diagnostic tool. To more comprehensively estimate the diagnostic sensitivity and specificity of this IgG ELISA for detection of infection with M. bovis in cattle and to define a suitable cutoff for use in the field, we further assessed its performance in experimentally infected calves in a closed beef herd and by applying Bayesian latent class modeling to laboratory testing results from 7,448 cattle entering Australian feedlots. The most effective cutoff points were estimated to be 68.6 antibody units (AU) for experimentally infected calves and to be 58.7 AU for a closed adult herd. Under field conditions, in feedlot cattle the globally optimal cutoff was estimated to be 105 AU. At this cutoff, the diagnostic sensitivity was 94.3% (95% probability interval [PI], 89.9% to 99.6%) with a diagnostic specificity of 94.4% (95% PI, 90.3% to 99.6%). Applying this 105 AU cutoff, 13.1% of cattle were seropositive for infection with M. bovis on entry into feedlots, and 73.5% were seropositive when followed up approximately 6 weeks later suggesting a high risk of infection shortly after entry into feedlots. Mycoplasma bovis is regarded to be an emerging cause of bovine respiratory disease (BRD) in veal calves, and infection can also cause polyarthritis and/or otitis media. In adult cattle, M. bovis is mainly associated with mastitis, keratoconjunctivitis, and reproductive tract disorders. Outbreaks of pneumonia induced by M. bovis have been reported throughout the world (1-3) and cause economic loss due to reduced weight gain and increased medication costs (4). The importance of M. bovis has been increasing because of increasing resistance to antimicrobial agents (5) and the lack of an effective vaccine (6). Transmission can occur through fomites, contact, or aerosol, and subclinically infected calves are believed to be carriers for life, so comingling of animals from different farms and age groups, combined with transport stress, results in outbreaks shortly after arrival in feedlots (7). Therefore, identification of infected source herds before introduction of animals to a naive group may help to prevent outbreaks (6).The gold standard for diagnosis of M. bovis infection is culture of the organism, but this is time-consuming and laborious. A M. bovis-specific PCR assay has been developed (8), but such assays are unlikely to be useful for herd screening, as excretion is only detectable for a limited time after infection. Serological diagnosis can be sensitive and inexpensive...

Polioencephalomalacia was diagnosed histologically in cattle from two herds on the Darling Downs, Queensland, during July-August 2007. In the first incident, 8 of 20 18-month-old Aberdeen Angus steers died while grazing pastures comprising 60%Sisymbrium irio (London rocket) and 40%Capsella bursapastoris (shepherd's purse). In the second incident, 2 of 150 mixed-breed adult cattle died, and another was successfully treated with thiamine, while grazing a pasture comprising almost 100%Raphanus raphanistrum (wild radish). Affected cattle were either found dead or comatose or were seen apparently blind and head-pressing in some cases. For both incidents, plant and water assays were used to calculate the total dietary sulfur content in dry matter as 0.62% and 1.01% respectively, both exceeding the recommended 0.5% for cattle eating more than 40% forage. Blood and tissue assays for lead were negative in both cases. No access to thiaminase, concentrated sodium ion or extrinsic hydrogen sulfide sources were identified in either incident. Below-median late summer and autumn rainfall followed by above-median unseasonal winter rainfall promoted weed growth at the expense of wholesome pasture species before these incidents.

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Mycoplasma bovis is associated with several clinical syndromes of cattle. Currently, limited information is available on the sensitivity (Se) and specificity (Sp) of serological assays used for the detection of M. bovis-specific antibodies. Consequently, it is difficult to critically evaluate the outcomes of studies that use these assays. Therefore, the current study used bovine sera sourced from M. bovis exposure studies from three countries to estimate the Se and Sp of two commercial M. bovis enzyme-linked immunosorbent assays (ELISA), BIO K302 and BIO K260, and Western blotting. Western blotting had the highest Se estimate of 74% (95% confidence interval (CI): 16–98%), compared to the BIO K302: 47% (95% CI: 10–87%) and BIO K260: 28% (95% CI: 1–92%). However, for Sp, the BIO K302: 96% (95% CI: 87–99%) and the BIO K260: 100% (95% CI: 93–100%) out-performed Western blotting: 88% (95% CI: 56–98%). Western blotting was the best assay for detecting seroconversion, correctly identifying 61% (95% CI: 29–86%) of exposed animals compared to 35% for BIO K302 (95% CI: 21–54%) and 8% for BIO K260 (95% CI: 0–87%). While none of the methods assessed had high Se and Sp, the availability of these estimates will aid in the interpretation of studies that use these assays. The results of this study highlight the difficulties encountered when using serology to detect exposure to M. bovis in cattle.

The preliminary results demonstrate detection of M. bovis in samples from all feedlots studied. When considered in the context of the reviewed literature, they support the inclusion of M. bovis on the list of pathogens to be considered during investigations into BRDC in Australia.

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Mycoplasma bovis can be a commensal bacterial inhabitant of the upper respiratory tract of healthy bovines. However, under certain circumstances and conditions that are incompletely understood, M. bovis can be associated with a number of clinical syndromes, one of which is bovine respiratory disease (BRD). In Australia, there is little information on the prevalence and epidemiology M. bovis in beef production systems. The overall aim of this thesis was to help close this knowledge gap.Commercially available serological diagnostic methods for the detection of M. bovis-specific antibody have not been validated in the Australian cattle population. Arguably, more importantly, however is the fact that diagnostic sensitivity (Se) and specificity (Sp) and / or analytical sensitivity (ASe) and specificity (ASp) estimates for commercially available M. bovis sero-diagnostic tests are not available. 28% (95% CI: 1% -92%). However, in terms of Sp the commercial ELISAs out performed western blotting; BioK302: 96% (95% CI: 87% -99%); BioK260:100% (95% CI: 93% -100%) and western blotting: 88% (95% CI: 56% -98%) respectively. In terms of both Se and Sp combined, none of the methods assessed here performed well. As such, when interpreting the results obtained from these ELISAs, the potential impact imperfect Se and / or Sp can have needs to be considered.Despite the poor performance of the BioK302 and BioK260 ELISAs particularly in terms of Se, these tests were used to determine the sero-prevalence of M. bovis antibody in Australian feeder cattle at feedlot induction and draft (approximately 42 days on feed). Paired bovine sera from 1,354 randomly selected animals were sourced from a bovine serum bank (n = 35,160) collected as part of another study, The National Bovine Respiratory Disease Initiative. As the classification of the result of a single serum sample could differ between the BioK302 and BioK260, sero-prevalence estimates were obtained using the individual ELISA results in addition to series and parallel interpretation of the two ELISA kit results. The apparent sero-prevalence of M. bovis-specific antibody at feedlot induction estimates ranged from 2.4% -6.8% (95% CI: 1.3% -8.6%) and the apparent sero-prevalence estimates at draft ranged from 22.4% -44.2% (95% CI: 19.1% -48.6%). The level of sero-conversion to M. bovis between induction and draft was also determined. Only animals that were classified as sero-negative at induction were included in sero-conversion analyses. In the current study, 24.3% (95% iii CI: 20.8% -27.7%) and 19.5% (95% CI: 17.3% -21.7%) of animals sero-converted to M. bovis between induction and draft based on the BioK302 and dichotomised BioK260 ELISA results respectively.Using these ELISA results, an assessment of putative risk factors associated with sero-positivity at feedlot induction or sero-conversion between induction and draft was performed. An increased risk of sero-positivity at feedlot induction was found to be associated with; (i) history of exposure to a saleyard at least 27 d...