Medical case studies are a great way for physicians and curious non-medics to learn about some of the rare diseases and conditions out there. But considering how many dangerous and often unsightly afflictions a human can encounter, sometimes perusing these articles can make certain people a little paranoid.

This particular case involves a man who became infected with an extremely virulent bacterium that he caught from his cat, but bear in mind that this disease is pretty rare, even among pet owners. Plus, if you do have a cat, you should be much more concerned about the toxoplasma protozoan that might already be holed up in your brain and possibly altering your behavior.

As described in The New England Journal of Medicine, a 68-year-old from Missouri was recently diagnosed with glandular tularemia, one of six manifestations that an infection with Francisella tularensis bacteria may take. F. tularensis is found around the world, but the strain that poses a threat to humans occurs predominantly in North America. The bacteria can live inside a variety of animals – it has been reported in mammals, birds, reptiles, fish, and invertebrates – and may persist between hosts in soil or water for several weeks. Transmission occurs when a suitable new host consumes contaminated water or organic tissue, inhales bacteria, gets bitten by something like a tick, or makes skin contact with a source of infection.

As few as 10 to 50 bacteria are all it takes to seed a tularemia infection, and without treatment, the disease is fatal in up to 60 percent of cases (though the glandular form is less lethal than the systemic or lung-based forms).

Thankfully, the bacteria is currently susceptible to several common antibiotics, so the only significant challenge for modern cases is making a prompt diagnosis, notes Mayo Clinic.   

The patient at the heart of this story presented to the Barnes-Jewish Hospital in St. Louis with three highly swollen, red, painful-to-the-touch lymph nodes that he claimed had been increasingly bothersome and inflamed ever since he experienced a week-long fever about two months ago. When asked if anything noteworthy had happened at the same time, the patient recounted that two days before his fever started, his cat had died. Apparently, a veterinarian had diagnosed the man’s cat with feline leukemia without doing any tests and told him to treat his cat with prednisone.

Now, as anyone who has had to give a cat medication can imagine, this process undoubtedly involved close contact and maybe even a few bites and scratches – a perfect opportunity for F. tularensis to jump from cat to human. You see, feline tularemia has similar symptoms as the feline leukemia virus, and although a course of immune system-suppressing steroids can help a cat's body recover, such treatment may quickly kill an animal with a bacterial infection.

Taken altogether, the symptoms and past exposures were a perfect match for glandular tularemia but physicians Laura Marks and Andrej Spec needed to be sure. Because F. tularensis is listed as a potential biological warfare agent, culturing the microbe requires elaborate safety protocols; thus, the go-to laboratory method is to look for antibodies against the bacteria in the blood. The man's antibody test came back positive, so the physicians initiated a three-week course of doxycycline.

The lesions were completely gone by week three.

To catch a tularemia infection in yourself or your pet before it progresses dangerously, be on the lookout for the symptoms described above, as well as loss of appetite, dehydration, pneumonia, abscesses or ulcers, and an enlarged spleen or liver.