Orange White KittenAnytime you see a case report in the medical literature, you know it must be something rare or new. Otherwise, no one would publish the occurrence of a single case. That can skew people’s perceptions because weird things get more attention.

So, it’s always hard to say what we should think about one-off reports of zoonotic infections. Is it the tip of the iceberg, with a lot of cases being missed? Is it an emerging threat? Is it a one-in-a-million fluke?  Often, it’s hard to say which of those might be true.

With those disclaimers in mind, here are a couple reports.

First reported human case of native mitral infective endocarditits caused by Streptococcus canis (Amsallem et al, Can J Cardiol 2014)

Streptococcus canis is somewhat of the dog equivalent to human Group A strep. It’s found in a lot of healthy dogs and usually doesn’t cause a problem, but can cause severe disease. It can also cause disease in people, but that is quite rare.

This case report is about a 65-year-old woman who developed infection of a heart valve. She needed an emergency valve replacement but recovered. The source was assumed to be her dog, but no unusual contacts such as a bite were reported. As is common, there appeared to have been little further investigation, and the dog was not tested to see if it was the source. Testing of the dog isn’t something I’d recommend as a routine measure in response to a human infection, but when it’s being published, a little more investigation would be nice.

Pasteurella multocida infection after solid organ transplantation (Christenson et al, Lancet Infect Dis 2015).

This one’s maybe less of an oddball case in that Pasteurella multocida, a bacterium commonly found in the mouths of healthy dogs and cats, is well recognized as a cause of infection in situations where it can get past the body’s normal protective barriers. Often, that’s because of bites or licking of broken skin. In this case, the infection probably occurred because of a combination of that and a profoundly weakened immune system because of the transplant.

The affected person was a 66-year-old man who had a kidney transplant. He had two dogs and a cat “with which he was very close.” He developed sepsis (a severe bloodstream infection) and subsequently died. It was suspected that the cat licking some ulcers on his leg was the source of the bacterium, but there was no subsequent investigation.

Low but ever-present risk

Both of these reports involve infections caused by bacteria that are commonly found in healthy dogs and cats. Human infections are rare, despite presumably very frequent exposure. This highlights the low but ever-present risk, and the need for basic infection control and hygiene practices to reduce the risk of infection. A few basic steps such as hand washing and keeping animals away from compromised body sites go a long way.