Science Questions

Is a human bite worse than a dog bite?

Hi, My name is Page. I am a student at the University of North Texas in the US and I love the podcast of the Naked Scientists. Is it true that a dog's mouth is cleaner than a humans? Or is it that the normal flora of a human more virulent than a dog's normal flora? Thank you. Page Barbalena

We posed this question to  Dr Nick Brown, Medical Microbiologist and Andreas Karas, Consultant Microbiologist, both from the Health Protection Agency...

Nick - Well, you might think that the dog bite would be the more dangerous and certainly of course, in terms of trauma, and particularly if related to attacks, they can be very nasty.  But actually, in terms of infections, then human bites have a very high incidence of complications.  And so, many people would actually say that human bites are nastier than dog bites.  So, all our mouths and all animal mouths are full of bacteria all the time and the sort of organisms that cause this infection are the things like Streptococci and Staphylococci particularly.  But the importance of the bite of course is that because of the teeth and the trauma that’s  associated with it and then those organisms can be introduced deep into the tissues where they can replicate and cause infections.

Andreas - The question about whether a dog bite or human bite is worse would depend largely on where in the world you are.  If you were in the developing world, rabies becomes a major factor and you would much rather be bitten by a human where rabies is much less likely.  If you were in another part of the world, it would depend a lot on the site of the bite.  Human bites in my experience are always much worse as they're often on the face, genitalia, really bad parts of the body, so probably better to go for dog.  But if you had an equivalent bite for the same size bite on let’s say your leg by a human or a dog, it’s probably much over muchness. Generally humans probably have a more diverse flora and larger number of different organisms.  Dogs have a lower number of organisms.  But either of their mouths would have hundreds of different bacteria in them of different types, and the ones that do the damage are really anaerobes.  Dogs have a particular organism called Capnocytophaga canimorsus, which can – if it gets into your bloodstream, can give you very severe blood poisoning.  And there’s a lot of talk about human bites being worse and dog bites.  Probably slightly true, not much evidence to prove that.  I would say, probably if I were to choose, I’d go for dog in the developed

Diana - In some cases, human bites can be worse than a dog bite, but this is dependent on how deeply the teeth penetrate the skin.  There are some nasty bacteria living in our mouths, but populations vary between individuals almost as much as they vary between species.  But if your dog has rabies, then you're probably better off being bitten by a person.  Many of the infections hospitals see which come from human bites are actually where someone has punched another person in the face, but their skin was broken when it came into contact with the recipient’s teeth.

March 2010