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Mycoplasma in Bison

Murray Woodbury DVM, MSc.

Specialized Livestock Health and Production
Department of Large Animal Clinical Sciences
Western College of Veterinary Medicine,
University of Saskatchewn
Saskatoon,Saskatchewan    S7N 5B4

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Mycoplasma infection is emerging as one of the most important diseases and sources of economic loss that bison producers have had to face. While occasional outbreaks of mycoplasma pneumonia and arthritis have been known to occur in the North American bison industry over the last decade, an ongoing morbidity and mortality study of feedlot bison in Alberta has recently identified this pathogen as a primary cause of respiratory disease in bison.

Veterinary pathologists and industry veterinarians have met recently to discuss some economically devastating Mycoplasma bovis outbreaks occurring in cow-calf operations across the US and Canada. These outbreaks are unique in that they frequently involve infection of mature animals, a situation rarely seen in beef cattle production.

In beef cattle, mycoplasma is a secondary or tertiary pathogen and is usually found in chronic cases of Respiratory Disease Complex in stocker and feeder calves and occasionally in nursing calves in cow-calf operations. In bison, M. bovis appears capable of acting as a primary pathogen. It has been isolated in pure culture as the sole isolate from fatal cases of pneumonia in the Alberta study and in other instances as well. Mature bison cows and bulls on pasture have suffered high morbidity and mortality rates and, where animals have recovered, chronic issues of infertility and ill-thrift remain. Calves at foot appear to be unaffected except that they often suffer malnutrition and may die from other causes if their mother succumbs while they are still nursing.

In November 2011, a group of interested veterinarians, scientists, and bison industry leaders assembled to discuss the significance of the apparent industry-wide increase in mycoplasma disease. Several priorities were established for the scientific investigation of the emerging problem. To address these priorities information on outbreaks and research material in the form of bacterial isolates and necropsy samples is required. Therefore, this group is appealing to veterinarians and bison producers to report possible occurrences of mycoplasma disease to state or provincial laboratories to assist these investigations.

A broad case definition has been developed to assist in the identification of disease possibly caused by mycoplasma. At the herd level, any unusually high incidence of disease or death affecting mature animals and/or young stock, with or without an association with reduced fertility (high numbers of open cows or abortions) is of interest. The following signs in an individual bison might indicate mycoplasma disease: weight loss and/or reluctance to move; progressing to coughing, difficulty breathing, lethargy, exercise intolerance, isolation from the herd and severe weight loss often resulting in death or euthanasia.

On post mortem, the following findings are indicative of mycoplasma disease: poor nutritional condition and the presence of severe, sometimes unilateral, fibrinonecrotizing pneumonia, sometimes pleuropneumonia with prominent pulmonary sequestra formation (figures 1 and 2). Widespread dissemination (hematogenous) of the infection is common but sites of the disseminated lesions are inconsistent and may include tonsils, pharynx, larynx, mediastinal and/or abdominal lymph nodes, peritoneum, pericardium, liver, spleen, kidney, mammary gland, endometrium and joints. Lesions at distant locations are typified by areas of caseous necrosis. Diagnosis is confirmed by the presence of histopathologic lesions of brightly eosinophillic necrosis typical of M. bovis infection in combination with the identification of the organism by immunohistochemistry, PCR, or culture. Finding concurrent viral or bacterial pathogens is uncommon and inconsistent.

Figures 1 and 2

M bovis lungs

Figure 1 - Pulmonary sequestra Figure 2 - Fibrinous pleuritis

Producers and their veterinarians can assist investigators by alerting their provincial or state pathology labs about possible disease outbreaks fitting the above description. They can also help by participating in the surveys and questionnaires that will be circulating in the industry in an effort to gain important epidemiological information about the risk factors involved in mycoplasma disease transmission. A cooperative effort will help to minimize the impact of mycoplasma disease on the bison industry.

Submission of diagnostic material from suspect cases can provide much needed bacterial isolates for test development, scientific study, and possibly vaccine construction. Producers and clinical veterinarians may submit diagnostic material to local provincial or state veterinary labs. Diagnostic labs may help research efforts by sending M. bovis isolates to Dr Karen Register (email: karen.register@ars.usda.gov) at the Virus and Prion Research Unit, Agricultural Research Service, USDA, P.O. Box 70, 1920 Dayton Ave., Ames, IA, 50010. Contact Dr. Register for more information, submission forms, and the appropriate USDA shipping/import permit.