A letter in Emerging Infectious Diseases (Ludwig et al 2011) describes an uncommon Mycobacterium infection in a pet ferret, with potential human health concerns.
The three-year-old ferret from Germany was taken to a veterinarian with a five-month history of coughing, recent weight loss, vomiting and mild diarrhea. A chest radiograph was taken and "nodular densities" were found in the lungs (these would show up as white spots on the radiograph). This type of finding is usually an indication of something bad going on in the lungs, such as tumours or granulomas. Because of the poor prognosis, the ferret was euthanized. At necropsy, the lung nodules were confirmed, and there were some other abnormalities such as and enlarged spleen and a lot of enlarged lymph nodes. Using a combination of culture and molecular tests, Mycobacterium celatum infection was identified as the cause.
Mycobacteria are a diverse group of microorganisms, whose most notable member is M. tuberculosis, the cause of (not surprisingly) tuberculosis (TB) in humans. Mycobacterium celatum belongs a large group classified as ‘non-tubercular’ Mycobacterium species.
Mycobacterium celatum is rather uncommon, being first diagnosed in a person with AIDS in 1993, and only being reported sporadically in people since then. Most human infections have occurred in people with compromised immune systems, but there are some reports of people with apparently normal immune systems becoming infected. There is also one previous report of an infection in a ferret. There is no evidence that the ferret reported here had a compromised immune system, so the reason for the infection is not apparent. The source of infection is also unknown. Since there were granulomas throughout the lungs, it suggests that the ferret inhaled the organism, but that can’t be proven and there are no clues even suggesting a possible source.
An interesting aspect of this report is the question about whether the ferret’s owner may also have been infected. It’s perhaps a bit of a stretch, but there was a suggestion that the owner may have been infected as well because he/she reported a chronic cough. Testing was performed and no Mycobacterium (of any species) was detected, but the person was treated with antibiotics prior to being tested so a false-negative culture is possible. The likelihood that the person was truly infected is probably quite low, but it can’t be dismissed.
Ferret owners shouldn’t be too worried about M. celatum. This is an example of one of many possible rare infections that can be encountered. Similarly, this report doesn’t mean that ferrets should be considered at higher risk for causing human infections. Every animal poses some degree of risk to people, and ferrets are actually pretty low-risk overall. Mycobacterial infections aren’t something to be too concerned about, but, as suggested in this report, the general concept of considering human disease when something is diagnosed in a pet is excellent and too often overlooked.
(Photo credit: Luke Rutherford)