[thedoc (OP)]

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.
Asked by Page Barbalena

               
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[thedoc (OP)]

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 of a 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 than 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 world...

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.

[sharkeyandgeorge]

unlikely, the idea that dog bites are cleaner than humans is somewhat based on the infection statistics for both types of bites, historically a greater percentage of recorded human bites have become infected but this is mainly down to the fact that if a dog bites you you go to the doctor and get preventative treatment however if your child bites you your likely to treat it yourself and only go to a doctor, where it is then recorded, if it becomes infected thus skewing the statistics.

[RD]

Some of the species of microorganisms in the dog cannnot colonise a human,
whereas all the microorganisms in a human mouth, (by definition), can.

So being bitten by a member of your own species can be more hazardous than being bitten by different species
because all their bacteria and viruses can colonise you.

Differences were noted in the microbiology of human bite wounds and animal bite wounds . The most striking difference was the higher number of isolates per wound in human bites compared with animal bites (5.4 versus 2.8 isolates per specimen).

http://www.ncbi.nlm.nih.gov/pubmed/12825249

[gixxor]

wow...never thot so

[Jessica H]

Seems the punishment doesn't fit the crime then.

A dog that bites gets put down, while my 2-yr-old daughter just got a note sent home from school.
 []

[geo driver]

you saying that you daughter should be put down jess  []

however a child bites once, a dog wont stop.

[thedoc (OP)]

Did we mention your answer on air?  Go to the podcast page to find out...
or [chapter podcast=2537 track=10.03.28/Naked_Scientists_Show_10.03.28_5991.mp3] Listen to the Answer Now[/chapter] or [download as MP3]

[Anon]

if its taught not to bite a dog will stop it doesnt deserve to put down anymore then a babie unless its completly rabid and cant be taught not to bite

[davidk]

One circumstance deserves mention.  Human 'bites' are not uncommon as a result of one person punching another in the mouth.  The injury thus obtained frequently involves penetration into the hitters metacarpo-phalangeal joints, sometimes accompanied by fractures.  Any contaminated injury involving a joint, whether it be canine, human or other, is more serious.  Infection here is harder for the immune system to access and complications are disabling.  This type of injury is overwhelmingly associated with human teeth rather than dog bites and largely is responsible for the human bites' reputation.

[chris]

Thanks @davidk - very valid points. One thing not mentioned in the answer above is that we frequently have to consider post-exposure prophylaxis against blood-borne viral infections (HIV, HCV, HBC) in people with hand lacerations incurred in the course of resolving a dispute or two with a third party.

[Liaata]

I got bit by a dog and went to the doctor. He told me that a dog bite is not very dangerous in terms of infections. He said a cats bite us worse and a humans bite is the most dangerous one.