Q: My cat recently started having diarrhea, so I took her to my veterinarian, who then referred her to a veterinary internist. After an extensive work-up, no cause for my cat’s diarrhea was identified, and it continued fairly consistently.

When I started to have diarrhea myself, I suspected that something was wrong and consulted with my physician, who diagnosed me with a Clostridium difficile (C.diff) infection. After 14 days on antibiotics, my diarrhea resolved but returned two weeks later.

Suspicious, I took my cat’s liquid stool to a veterinary microbiologist, who found C. diff. Can you advise me about how to eliminate C. diff in my cat? 

A: Thanks for getting in touch, and I am very sorry to hear of the problems that you and your cat have been experiencing. As you have probably learned, C. diff is a somewhat enigmatic organism in that it can cause serious disease in some individuals but can also be found in the GI tracts of healthy individuals. Perhaps a brief review of what we know about C. diff and its impact on cats would be helpful.

C diff is an anaerobic bacterium (i.e., it thrives in environments with low oxygen) that is found in humans, a variety of animal species, and the environment. It can be found in two states: a vegetative form that multiplies in the GI tract and a spore form that is passed in the feces and can survive in the environment for long periods of time. This spore form is the infectious form, and individuals become infected by ingesting environmental spores.

Disease is caused in infected individuals by three toxins that some strains of C. diff produce, called toxins A, B, and CDT, respectively. Strains that do not produce these toxins are generally considered to be benign.

The toxins that some strains of C. diff produce can damage the lining of the GI tract, resulting in diarrhea, vomiting, nausea, abdominal pain, fever and blood in the stool in more severe cases. Importantly, many people and animals carry C. diff in their GI tracts without showing any signs of disease, usually because the strains they carry do not produce the toxins mentioned above and/or because their growth and activity is kept in check by other (beneficial) bacterial species.

If the growth of these beneficial bacteria is inhibited (by antibiotics, for example), then potentially harmful strains of C. diff can overgrow and cause disease via the production of one or more of these toxins.

C. diff has been isolated from the GI tracts of both healthy cats and those experiencing GI symptoms, usually diarrhea. It is estimated that 3% to 5% of healthy cats shed C. diff spores in their feces while showing no adverse health effects, and that as many as 35% of cats harbor this bacterium in their GI tracts.

In many cases, the strains of C diff that cats harbor are the same as those found in people, and while there is some anecdotal evidence that supports the notion of both cat-to-human and human-to-cat transmission, the risk of this type of inter-species transmission is currently believed to be relatively low.

A very important point to note is that we do not definitively know that C. diff causes diarrhea in cats. Attempts to eliminate it from your cat’s GI tract (i.e., with antibiotics) may not only be of questionable benefit, but may also be harmful in that the delicate balance between the various species of bacteria that reside in her GI tract may be upset, which can result in significant GI disease.

Please discuss these issues with your veterinarian, as it is possible that your cat’s GI signs are due to other disease processes (i.e., inflammatory bowel disease, food sensitivity, or GI lymphoma), and that the finding of C. diff in her GI tract is a “red herring.”

Best of luck, and please send us an update when you can.