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An Emerging Disease of Ferrets: Disseminated Idiopathic Myositis
Julia Whittington, DVM
November 17, 2005
Ferrets, Mustela putorius furo, are small mammals belonging to the order Carnivora and are a probable descendant of the European polecat. Although kept as domesticated animals since 400 BC, the popularity of ferrets as pets has been rapidly increasing in North America and Europe. Ferrets are friendly, fun-loving animals and make remarkably good pets. So it is with frustration that veterinarians and ferret owners are faced with an emerging disease that has no known cause or cure.
Disseminated Idiopathic Myositis (DIM) was first described in 2003 and generally results in a fatal inflammatory condition of the muscles. To date, over 40 suspected cases have been identified. Animals diagnosed with DIM are typically young, between three and 21 months old, with both males and females affected. The sources of the ferrets are variable, as are their vaccine histories.
The clinical signs of DIM in ferrets are non-specific with most ferrets displaying lethargy and fever. Additionally most ferrets have a decreased appetite and a reluctance to move around. Some ferrets with DIM will have one or more enlarged lymph nodes or other swellings not associated with lymph tissue. The fever is generally persistent and will fluctuate, becoming as high as 108 degrees F in some cases. Many of these ferrets become dehydrated and develop poor body condition as a result of the fever and decreased food intake. Some ferrets with DIM develop diarrhea, mild serous nasal discharge, with increased heart and respiratory rates as well.
Diagnostic testing of affected ferrets often show markedly elevated white blood cell counts with significant increases in inflammatory cells, neutrophils. They may also have a mild to moderate anemia. Radiography and ultrasonography are usually unremarkable. Histopathology of skeletal muscle, heart and esophagus of ferrets with DIM typically have severe suppurative to pyogranulomatous inflammation. Biopsies of skeletal muscle from the hind leg or lumbar region or from lymph nodes and masses may be useful for antemortem diagnostic purposes.
Many different therapies have been attempted in efforts to reduce the fever and inflammation associated with this disease. Antibiotic therapy including penicillins, cephalosporins, fluoroquinolones, doxycycline, clarithromycin, azithromycin, trimethoprim-sulfa, aminoglycosides, metronidazole, and chloramphenicol have been unsuccessful. Treatment with steroidal and non-steroidal anti-inflammatory drugs also have little effect. Other drugs including antifungal and antiviral agents have been ineffective in controlling signs of DIM. Interferon-alpha at a dose of 600 IU/day has been shown to reduce the fever in a few cases.
At this time, the etiology of DIM is unknown. No pathogen has been isolated in any of the confirmed cases. Bacterial infection is still considered a possibility due to the suppurative nature of the inflammation seen.
Recent recommendations include treatment of suspected DIM ferrets with prednisone and cyclophosphamide due to the suspicion that DIM may have an immune-mediated component based on the lack of response to effective treatment for most pathogens.
Veterinarians or ferret owners who suspect DIM in a ferret are encouraged to visit the American Ferret Association website at www.ferret.org for more information on the disease. Specific information for veterinarians with suspected cases of DIM is included on the site.
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