Abstract
The on-site Molecular Diagnostics Laboratory of the Zoological Society of San Diego investigated an outbreak suspected to be a foreign animal disease. Within a 4 wk period in February 2003, three male Vaal rhebok (Pelea capreolus), endangered South African antelopes, were presented to the veterinary hospital for evaluation of subdued behavior and decreased appetite of 24 hr duration. Additional clinical signs were variable and included ataxia, increased bronchovesicular lung sounds, excessive salivation, and head tremor. Radiographic changes supported a respiratory disease component in each case. Despite supportive treatment, all three were either euthanatized or died within 2 days of presentation.
Post-mortem examination showed that the animals had one or more lesions consistent with a systemic infection (pneumonia, cellulitis, and lymphadenitis). However, the etiology could not be determined histologically. The affected animals also had USDA permanent post entry quarantine (PQ) status that severely hindered the amount of diagnostic testing that could be done outside the grounds of the San Diego Zoo. Consequently, the zoo relied on its on-site Molecular Diagnostics Laboratory to investigate possible viral or bacterial etiologies.
Using polymerase chain reaction (PCR) methods, the laboratory found that the animals were infected with Mycoplasma of the mycoides cluster. These mycoplasmas are of particular concern, in that all species of this cluster are pathogenic in ruminants, and thus have a tremendous effect on livestock industries by causing death and disease in cattle, goats and sheep.3 The mycoides cluster of mycoplasmas consists of six species that are closely related genetically and phenotypically.4 Among these, Mycoplasma mycoides subsp. mycoides small-colony (MmmSC) and Mycoplasma capricolum subsp. capripneumoniae (Mccp), which are the causes of contagious bovine pleuropneumonia (CBPP) and contagious caprine pleuropneumonia (CCPP) respectively, are of particular concern. These mycoplasmas are classified by the Office International des Epizooties as A and B list pathogens1,2 and are considered to be foreign animal diseases in the United States because of the threat they pose to domestic animals.
Due to the possibility of the agent being a foreign animal pathogen, the USDA was notified and archived samples from affected animals were submitted for evaluation. The USDA excluded the presence of MmmSC and Mccp, and confirmed our results that the disease-causing agent is a Mycoplasma of the mycoides cluster. However, the zoo was still faced with the dilemma of an infectious Mycoplasma that had caused acute disease in the rhebok, and could possibly affect other animals. Further molecular analysis allowed the identification of each species of infecting Mycoplasma, and the development of diagnostic tests to track possible contact animals. The results of this study illustrate that although mycoplasmal infections are ubiquitous and usually non-pathogenic, some species of animals can be particularly susceptible to them. The ability to use on-site molecular diagnostics in the disease investigation of PQ status animals can be an invaluable tool in determining the possible cause of the disease, and in future prevention of outbreaks through surveillance.
Literature Cited
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2. Rurangirwa FR, JH Kinyili. 2000. Contagious caprine pleuropneumonia. In: M Truszczynsky, ed. Manual of Standards for Diagnostic Tests and Vaccines. 4th ed. Office International des Epizootes (O.I.E.), Paris, France.
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