There is this myth that a dog’s mouth is cleaner than a human’s mouth. I don’t think so. Yeah, an animal that neither brushes nor flosses and, depending on the breed, can lick its ass has a cleaner mouth than a human. Right. Seem believable only if the comparator human has meth mouth. But otherwise? Not so much.
I suspect, and this is just an edumacated guess, it is due to the circumstances surrounding the bites. A dog’s bite is often a ripping and tearing injury and those with the bite get to the emergency room ASAP for care. Human bites are often one drunk male hitting another drunk male in the mouth or getting bit, and due to the inebriation, there is delay in seeking care so the infection has an opportunity to fester. Cat bites tend to be injection injuries, the thin sharp teeth pushing bacteria deep into tissues with minimal tissue damage to I&D.
As one of many asides, although I watched the Adams Family as a youth, it wasn’t until I was late middle age that I realized the meaning of the name Uncle Fester. The Fester part, not the Uncle. Around the same time, I realized why the rocks next to Haystack Rock were the Needles. Nothing is as invisible as the glaringly obvious. Like Homeopathy is only water. Or Soylent Green is people.
Not that human mouths are all that clean. The mouth and teeth have a rich microbiome of Streptococci, anaerobes (depending on the dentition), non-syphilitic (one hopes) spirochetes, and a lot of other species.
The Oral cavity is one of the most well-studied microbiomes to date with a total of 392 taxa that have at least one reference genome and the total genomes across the oral cavity approaching 1500.[21]
Approximately 700 species of prokaryotes have been identified in it. These species belong to 185 genera and 12 phyla, of which approximately 54% are officially named, 14% are unnamed (but cultivated) and 32% are known only as uncultivated phylotypes. The 12 phlya are Firmicutes, Fusobacteria, Proteobacteria, Actinobacteria, Bacteroidetes, Chlamydiae, Chloroflexi, Spirochaetes, SR1, Synergistetes, Saccharibacteria (TM7) and Gracilibacteria (GN02).
You kiss your significant other with that mouth? You betcha.
None of these organisms are particularly pathogenic, at least locally. Suck some spit into an airway during a drug-induced stupor, they may cause a lung abscess. Get them in the blood, you may get a heart valve infection. How do these bacteria get in the blood? Brushing, flossing and picking. Those with oral Streptococci as a cause of endocarditis were more likely
…to use toothpicks, dental water jet, interdental brush, and/or dental floss (OR, 3.48; 95% CI, 1.30-9.32), and to have had dental procedures during the prior 3 months (OR, 3.31; 95% CI, 1.18-9.29), whereas they were less likely to brush teeth after meals.
And IVDA. Many an injection drug user will lick the needle just prior to injecting. Some because the needle slides in easier, some to taste the drug.
And with the drug some Streptococci go along for the ride and seed the heart valve. Although, as a variation on the theme (Infectious Diseases and Bach have a lot in common) I had one patient with a Neisseria sicca endocarditis likely from licking the blood off the infection site. Now don’t go ick, a show of hands, how many of you will stick a bleeding finger in your mouth?. No one? I’m it? OK.
Let’s move on.
Dogs do have an interesting oral microbiome with a few organisms that can occasionally become pathogenic. Streptococcus canis, Staphlococcus pseudintermedius, Capnocytophagia canimorusus and Pasteurella spp. Cats are most associated with Pasteurella infections, but most mammals have their own Pasteurella, including humans. Get bit by a bison? Could result in a Pasteurella infection.
Infections from Pasteurella associated with cats were not uncommon. My most memorable? The diabetic leg infection from walking barefoot with a foot ulcer in a house with dozens of cats, the peritonitis in the peritoneal dialysis patient whose cat slept in their bag warmer, and the teenager with meningitis who liked to put tuna on her nose for the cat to lick off. The veins around the nose drain straight back into the CNS, so every time you sqooze a nose zit, you were flirting with death. It is called the ‘triangle of death‘ for a reason.
It is hard to get infected. Most organisms are not pathogenic, and the few that can cause disease do so only rarely. Just often enough, I suppose, to give me a career.
I did see the occasional infection from dogs mouths that were not due to a bite. The most curious was the child with Pasteurella meningitis whose family dog liked to lick the head of the child. Kind of like trying to get to the center of a Tootsie Roll pop. And there was the occasional cellulitis of the leg from a dog associated Streptococcus due to the dog licking the feet of the patient. One patient, with severe neuropathy, had several episodes of cellulitis as he could not feel the dog licking. This can occasionally lead to the loss of a toe. Or two.
Never let your dog acquire a taste for sweet, sweet human flesh.
It has been noted that dogs will lick their wounds, occasionally past the point of benefit. Besides mechanically cleaning the wound, there are proteins in dog saliva with mild antibacterial effects and that perhaps aid in wound healing.
Canine saliva was tested for its bactericidal effects against pathogens relevant to the presumed hygienic functions of maternal grooming of the mammary and anogenital areas and licking of wounds. Both female and male saliva were bactericidal against Escherichia coli and Streptococcus canis but only slightly, and nonsignificantly, bactericidal against coagulase positive staphylococcus and Pseudomonas aeruginosa. E. coli is the cause of highly fatal coliform enteritis of neonatal mammals and E. coli and S. canis are the main pathogens implicated in neonatal septicemia of dogs. The bactericidal effects of saliva would facilitate the hygienic function of maternal licking of the mammary and anogenital areas in protecting newborns from these diseases.
Which is true of all body fluids, as without antibacterial effects, spit, tears and other body fluids would be nothing but bacterial and fungal growth media.
Human mouths are the same yet different.
The oral proteomes of dogs and humans were appreciably different. Proteins related to apoptosis processes and biological adhesion were predominated in dog saliva. Drug-target network predictions by STITCH Version 5.0 showed that dog salivary proteins were found to have potential roles in tumorigenesis, anti-inflammation and antimicrobial processes. In addition, proteins related to regeneration and healing processes such as fibroblast growth factor and epidermal growth factor were also up-regulated in dogs.
Humans put a lot of…..interesting…. things in our mouths. I will not be one to judge. But what goes in the mouth can be chock-a-block full of bacteria that cause us no harm because of extensive anti-bacterial systems. The immune system consumes 25-30% of the body energy production keeping the microbial world at bay. About the same as the brain or resting skeletal muscle. Like I said, it is hard to get infected by most bacteria.
But some, noting that dogs and other animals like rats lick their wounds, conclude not that animals should lick their wounds, but that their dog and cat should lick the human’s wound, in my practice most often a diabetic foot ulcer.
Most sites suggest having a dog lick your wounds is a bad idea. But not all.
If your cut is small, you may feel comfortable with your dog licking and attending to your wound. If that is the case, it is suggested that you allow your dog to lick your wound. It is important to make sure your dog has been fully dewormed and checked by the veterinarian. It can be helpful in trusting this process, so no infection is created. If your dog is not willingly trying to lick at your wound, it shouldn’t be something you push at. Your wound may be something that your dog does not desire to lick and it may be something your dog feels sick over, too, and does not like it. Therefore, if you feel safe and your dog desires to lick your wound, then it may be something to encourage and allow. Yet, it is important to do what is best for you, your health, and your dog.
Many are wishy-washy,.
Letting your dog lick your wounds may not always be harmful, but it doesn’t mean you should encourage your dog to do it. The bacteria in a dog’s mouth could give you an infection and there have been some rare cases where the infection has been life-threatening.
And, of course, there is TicTok, land of fools.
Many of the websites mention the usual dog pathogens and rabies as a risk. There is almost no dog rabies in the US thanks in most part to a vaccine and in part due to Atticus. If your dog has rabies, you have more to worry about than it gently licking your blackberry scratches.
By the way, I remain of the opinion that blackberries are sentient and attack like apple trees when you pick the fruit. And that the thorns are more painful than equally sized sharp objects. I do not know if it is the shape or if the thorn has an irritant. The topic has never been scientifically investigated. And I guess from last weeks Nature, they are prickles, not thorns.
Pubmed has 43 hits for dog lick infection, including the dread Capnocytophagia sepsis in the asplenic. Cats not so much.
As another aside, as a kid I thought the Scott decision was considered so awful, it was the dread Scott decision. Like the dread Pirate Roberts. Only late in life did I discover his first name was Dred. But I still think I was correct in spirit if not in fact.
First, I know dogs will eat vomit and shit, but still. Ick. For the dog. And as I mentioned, you really don’t want human to be part of your dog’s diet.
While there are animal models to show benefit from licking wounds, there are zero clinical trials comparing animal wound licking to standard care. I would suggest that while you may get away with a dog licking a wound, the intervention is no better than soap and water and certainly has the chance of starting an infection.
But I was always a minimalist for wound care. As a medical student a plastic surgeon attending opined that you should never put in a wound what wouldn’t put in your eye. I usually, but not always, followed that idea and treated wounds with contact lenses.
But animal spit? Bad idea.
Being licked by pet dogs is frequently a common advice in articles for the uninitiated. An overview is given about the special antibacterial and wound healing properties of human and canine saliva. New developments in the human area are presumably assigned to dog saliva. Because of the presence of a quite different mouth flora including various potential zoonotic pathogens, it is strictly not advised to let dogs lick the wounds or face of the human.
Plus, while we often share bacteria, nonpathogenic and pathogenic, with our pets, why go out of the way to give dogs our pathogens?
My rule, a parallel to ‘lips that touch wine shall never mine,’ is ‘animals that can lick their butt shall never lick my wound or cut.’
But a dog licking your wound is likely better than one alternative:
You should be aware of the case of an Oregon teacher who was reprimanded after licking the blood from wounds on a track team member’s knee, a football player’s arm, and a high school student’s hand.
I mentioned all this to my wife. Her response? “What is wrong with people?”
I can’t disagree. Kind of sums up this blog.