Evaluation of an IgG Enzyme-Linked Immunosorbent Assay as a Serological Assay for Detection of Mycoplasma bovis Infection in Feedlot Cattle

Abstract

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...

Bulk tank milk antibody ELISA as a biosecurity tool for detecting dairy herds with past exposure to Mycoplasma bovis

“…The low coefficient of determination value and weaker association in the current study may have been due, in part, to imperfect specificity of the ELISA in Australian dairy production systems. Although the specificity of this ELISA was high when used on individual serum samples from nonexposed calves (Wawegama et al, 2016), we observed seroprevalences in lactating cows varying from 6 to 22% in the 6 control herds with no known clinical history of mycoplasmosis. This may have been attributable to antigen cross-reactivity with other pathogens.…”

“…Finally, the absence of a close association may have been partly attributable to poor sensitivity of the Bio-X ELISA at the individual animal level. Sensitivity of this ELISA has been estimated as 37% (95% CI: 22-54) relative to an IgG ELISA in sera from individual animals (Wawegama et al, 2016) and 60% (95% posterior credibility interval: 38-96) in BTM (Nielsen et al, 2015). However, although not all herds with a known history of M. bovis disease had a positive BTM (≥37 ODC %), the BTM ELISA may be more useful in identifying absence or presence of previous exposure to M. bovis at the herd level.…”

“…A separate study evaluated the use of the ELISA on serum samples from individual calves experimentally exposed to aerosols containing M. bovis. Relative sensitivity and specificity compared with an M. bovis-specific IgG ELISA were 37% (95% CI: 22-54) and 95% (95% CI: 83-99), respectively (Wawegama et al, 2016). A third study investigated factors that may affect the BTM ELISA ODC%; a significant positive relationship was observed between the within-herd ELISA apparent prevalence in lactating cows (based on individual composite milk samples) and the BTM ELISA ODC% (Petersen et al, 2016).…”

Short communication: Shedding of Mycoplasma bovis and antibody responses in cows recently diagnosed with clinical infection

“…As M. bovis can be detected from body sites other than the mammary gland, such purchases pose a risk for the introduction of M. bovis. More recently, studies have evaluated the use of ELISA to detect animals previously exposed to M. bovis (and hence, potentially infected; Wawegama et al, 2016).…”

A review of mycoplasma diagnostics in cattle

“…Suggestions of poor sensitivity 63,115 Organism must be viable, therefore storage and handling of the sample is important 7,11 Animal must be shedding the organism at the time of sampling 26,28 Abbreviation: PCR, polymerase chain reaction.…”