ACVIM issues statement on M. bovis infection in cattle
MedWire News: The American College of Veterinary Internal Medicine (ACVIM) has issued a consensus statement dealing with Mycoplasma bovis infection in cattle, in which they provide evidence-based recommendations for the treatment and control of this important bovine pathogen.
M. bovis infection causes respiratory disease, otitis media, arthritis, mastitis, and a variety of other diseases, and has a substantial impact on the health, welfare, and productivity of dairy and beef cattle.
The infection can be difficult to diagnose and control, however, and the epidemiology and pathophysiology of M. bovis-associated disease is not well understood.
In the new consensus statement, an expert panel of the ACVIM led by Fiona Maunsell (College of Veterinary Medicine, University of Florida, Gainesville) critically reviewed the scientific literature, including peer-reviewed journal articles, reviews, and conference proceedings.
Based on this review of the evidence, they propose a number of recommendations intended for veterinarians dealing with cattle, with a particular focus on systems in North America.
In terms of diagnosis, the statement says that rapid and accurate diagnosis of M. bovis infection is compromised by the low sensitivity and specificity of available tests, as well as subclinical infection and intermittent shedding.
These limitations notwithstanding, infection can be detected serologically, using enzyme-linked immunoassay (ELISA) against M. bovis-specific serum antibodies, or from cultures of clinical material, using either ELISA or polymerase chain reaction.
With regard to treatment, it is well-established that mycoplasma mastitis responds poorly to intramammary or systemic antimicrobial drugs, and treatment of cows with the condition is not recommended.
In terms of specific antimicrobial agents, M. bovis is not susceptible to β-lactam antimicrobials or to sulfonamides and is resistant to erythromycin. However, it is generally susceptible to tetracyclines, macrolides, linosamides, florfenicol, and fluoroquinolones.
Two drugs are currently approved in the USA for treatment of bovine respiratory disease (BRD) associated with M. bovis: tulathromycin and florfenicol. A third drug, gamithromycin, is approved in this indication in Canada.
A few controlled trials have evaluated the efficacy of antimicrobials for the treatment of experimentally induced M. bovis-associated disease, with some success. There is less information on the treatment of naturally occurring infection, but the evidence in this setting generally supports early, aggressive antibiotic therapy.
Metaphylaxis can be appropriate in cattle with clinical M. bovis-associated disease, as is "strategic treatment" of cattle - particularly calves - at high risk for disease; however, vaccination efforts to date have been unsuccessful.
Looking to the future, the statement highlights a number of "priority areas" for research. These include the development of cost-effective, sensitive, and specific diagnostic tests; the collection of prevalence data to allow the true impact of M. bovis-associated disease to be determined; and more epidemiologic data on risk factors for infection and disease and the long-terms impact of infection.
"Perhaps the most critical needs are evidence-based strategies to limit the clinical, welfare, and economic impacts of M. bovis infection," write Maunsell and co-authors in the Journal of Veterinary Internal Medicine.
"Identifying these strategies will require well-designed field studies to critically evaluate vaccines, antimicrobials for treatment, or metaphylaxis or both, and management strategies for the control of M. bovis infections."
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By Joanna Lyford