The latest edition of Emerging Infectious Diseases (Berger et al 2011) describes a case of Corynebacterium ulcerans infection in a women that was likely acquired from her cat.

Corynebacterium ulcerans is a bacterium that’s related to C. diphtheriae, the cause of diphtheria. Some strains of C. ulcerans can produce toxins that cause diphtheria-like disease, and with the success of diphtheria vaccination, C. ulcerans is now the leading cause of diphtheria-like disease in people in some regions. Typically, C. ulcerans infections are associated with ingestion of contaminated milk or dairy products, but reports of infections acquired from dogs and cats appear to be on the rise. As is often the case, whether this is because it’s becoming more common or that people are simply looking more is unclear.

In this report, a woman from Germany developed diphtheria-like disease, including a sore throat, ear ache, hoarseness and nasal obstruction. A swab was taken from her nose and throat, and toxigenic C. ulcerans was isolated. She didn’t report any livestock contact and had not traveled abroad, so other possible sources of infection were considered, particularly other types of animal contact. She had a cat, so nose and throat swabs were collected from her pet, and the same strain of C. ulcerans was isolated.

With this type of investigation, you can’t prove that the cat gave the bug to the owner. Since the cat was healthy and tested after the owner was sick, you can’t say for sure whether the cat was the original source or if it was infected by the owner. However, with a bug like C. ulcerans that has been associated with pets before and that can be carried by healthy cats, the conclusion that it came from the cat is reasonable. The cat was treated with antibiotics and C. ulcerans was not detected after treatment.

This is an interesting report.  It’s always good to see people thinking about the relationship between human and animal disease, but at the same time, it’s important to put this into context. Yes, C. ulcerans is a potential zoonotic concern, but it’s rare. Anytime you see a case report involving a single person in the medical literature, you know it’s either something new or very rare. In this case, it’s the latter, since we know from previous reports that this bug can cause human infection and be transmitted from animals. Rare doesn’t mean never, and you can’t dismiss it, but C. ulcerans is just one of many bacteria that can be found in cats and transmitted to people. It’s part of the inherent risk of infection that comes with cat ownership. This relatively low risk is hopefully outweighed by the benefits of cat ownership, and the cost-benefit can be maximized by basic infection control and hygiene practices. This report also shows how it’s important for physicians to query pet ownership when dealing with infectious diseases in their patients, something that still needs lots of improvement.