Dog tongueCapnocytophaga canimorsus is a bit of an obscure bacterium. When I talk about it to veterinary or physician audiences, I’m usually met with blank stares – not surprising, since it’s not really mentioned in veterinary or medical school, from what I can tell. It’s a rare cause of infection, but a nasty one. The fact that it’s present in almost all dogs’ mouths and can cause fatal infections in people (especially people that are lacking a spleen or have a compromised immune system) makes the approach to managing it challenging. Virtually every dog poses some risk of a fatal infection, but the overall risk is very low.

The latest report about this particular bug is entitled “Lick of death: Capnocytophaga canimorsus is an important cause of sepsis in the elderly” (Wilson et al. BMJ Case Reports 2016).

The title is pretty misleading.

  • First, it should be noted that the patient survived the infection (but sepsis is very serious).
  • “important cause of sepsis” hardly applies to something that’s so rare that a single case warrants a publication.
  • There also wasn’t any proof that a lick was the source; however, it’s a reasonable assumption.

Regardless, the report describes the case of a 70-year-old woman that developed C. canimorsus sepsis (overwhelming bloodstream infection). She owned an Italian greyhound, and while no bites or scratches were reported (which doesn’t necessarily mean they didn’t occur), the dog licked her frequently. It was assumed that the source of exposure was a lick from the dog.  The bacterium would have had to enter the body through some broken skin, or through a mucous membrane (e.g. if the dog licked her face a lot and saliva got in the woman’s eyes, nose or mouth – not unheard of, unfortunately).

This report has lead to a variety of news articles (some straightforward and some very much over-the-top) about the risks associated with licking from pets.

Yes, licking is associated with some risk, but so are many other things in life that we do on a daily basis. I get asked about licking all the time. My standard response is that I don’t like my dog licking me, but that’s not a germaphobic thing, I just don’t particularly like it. For most people, the risk from being licked by a dog is low, but in some situations it’s higher, including:

Typical high risk groups: young children, elderly individuals, people with compromised immune systems and pregnant women. The highest risk groups for this bug in particular are people without a functional spleen and alcoholics. More care (or complete avoidance) should be taken by them.

Licking around the eyes, nose, moouth, ears and open wounds: this is riskier than licking intact skin.

Also remember that a little washing goes a long way. If there’s concern about saliva exposure, washing the site after an inadvertent lick probably helps a lot.

The “learning points” from the article are good:

  • Capnocytophaga canimorsus is a rare but significant cause of fulminant sepsis in pet owners.
  • Identification of C. canimorsus is facilitated by clinical suspicion and requires close collaboration with microbiology colleagues.
  • Infection may occur following close contact with a dog and does not require overt scratch or bite injuries.
  • Increased pet ownership and age-related immune dysfunction are thought to confer higher risk in the elderly.
  • Bacterial zoonoses from common household pets are frequently missed diagnoses.

For more information about this potentially nasty bug (and many others), check out the information sheets on the Worms & Germs Resources – Pets page.