[krool1969 (OP)]

I'm having an argument with a friend who lets his dog lick his spoon. He arguers that this is not gross because humans have quite a lot more bacteria in our mouths than dogs do. I argue that it is not the number of microbes that is important, but rather the species.

Because dogs use their tong for toilet paper they are likely to have fecal bacteria in their mouth, while humans use warm water or disposable paper to clean ourselves, then we (should) wash our hands after.

Another important question would be is there any kind of significant transfer of microbes shared between the two? In a Mythbusters episode they tested double dipping and discovered there was very little (if any) microbial transfer into the tub of dip.

[CliffordK]

I've seen dogs that think of horse apples as a delicacy. 

Many of the common human pathogens don't cross zoological species.  So, it is unlikely that you will catch the cold or flu from your pet.

However, I'm seeing the list of zoonotic illnesses that can infect humans is rather long.
http://www.2ndchance.info/zoonoses.htm
http://www.gopetsamerica.com/dog-health/zoonoses_dogs.aspx

Here are some notes about leptospirosis. 
http://www.seattlepi.com/lifestyle/health/article/Dog-disease-can-be-passed-to-humans-vets-warn-1169743.php

Here are some diseases transmitted with dog bites.
http://www.ehow.com/about_5467186_dog-bite-diseases.html
Likely they would be different with the mode of entry, a bite vs orally.

And, Cat Scratch Disease (from cats) can be problematic for some individuals too.
http://en.wikipedia.org/wiki/Cat_scratch_disease

Some of the zoonotic diseases won't be passed through saliva.  For example, worms may only be passed via feces. 

It is likely that if your friend has been sharing his spoon with his dog for some time, he and the dog may share some GI bacteria.  And, if the dog is healthy, the risk of getting something new from it would be low.

I wouldn't, however, share my silverware with any stray dog in the park.

You will note that some people will kiss their pets, and allow the pets to lick their face.  Is that any different?

[Airthumbs]

You have missed the fact that dogs like to clean their nether regions by licking them.  Several times I have seen a dog doing this and then an owner walk into the room and let the dog lick their face. 

I do not allow dogs anywhere near my food but they do occasionally manage to get a lick on my face, yuck!

[CliffordK]

There was a discussion earlier on whether a person could "self-infect" with their own GI bacteria.   I think the conclusion was that to a large extent, flora in one's system won't make one sick, unless allowed to multiply.

So, a cat or a dog grooming likely isn't a problem for themselves.   

The question then is how much "flora" does the owner and pet share.  Perhaps it would be quite a bit in some cases.

[evan_au]

On different aspect of "Is it safe to share your food with your dog?", we recently took our new puppy to puppy school, and the vet warned us not to share:

• chocolate
• onions
• cooked bones (they splinter)
• Corn cobs (cause intestinal obstruction)

One of chocolate/onions could cause a dog's red blood cells to break down!

A recent study showed that, compared to wolves, domesticated dogs have a copy-number variation in the amylase gene, allowing them to digest starchy food much more readily. It is suggested that this is because domesticated wolves/dogs hung around human trash heaps, and helped themselves to the scraps of human food (including cultivated starchy vegetables). So they are probably OK with most kinds of human food. 

...But I guess the question really was: "Are humans safe to share the leftovers of a dog's meal/saliva/etc?".

[evan_au]

Dog saliva has some antiseptic properties against some types of bacteria: http://en.wikipedia.org/wiki/Wound_licking
...but not others!

[Minerva]

I guess you could also ask if its safe to kiss a woman (women are much more likely to have faecal matter/bacteria on their hands than men) or touch your face/mouth/eyes after being in any public place.  If you live with an animal you will share GI bacteria eventually-it cant be avoided - so overt demonstrations like face licking just make us cringe because it draws attention to it (if you think too hard about avoiding bacteria you end up like Howard Hughes....).

When I worked in an office I got fed up with people using up the milk I brought in and never leaving any for me so I started bringing it in a large urine sample bottle (unused of course).  It was probably more sterile than the containers they brought theirs in but no-one wanted it..... 

Anyone know why my smileys don't work?

[menageriemanor]

evan au (and others), your list of what not to feed is very incomplete.  Many are unaware that grapes and their dried form, and raisins are toxic and can kill dogs.  This includes the manky but great for the garden, old crushings of grapes, sold as soil conditioner.  Many labs die from scoffing that, spread around the garden, as improver.

Macadamia and walnuts have an unknown toxin that can kill.  I know that the first symptom most owners may notice, for macadamia poisoning, is a cycling motion in hind legs, when moving, (an exaggerated stepping).  Mushrooms can make sick, baby food can have onion powder in it, (still toxic).  The list to avoid is huge and often every list is incomplete, PLUS remember sticks for throwing, if from oleander, could kill.  Sticks can be dangerous, dogs can run into a stick that has javelined into the ground, and run a stick into their throat, puncturing it.  Balls are far safer, but even then, size is important.  Nothing that could be easily swallowed, and block intestine.  Please read a number of lists.  It's amazing how many are incomplete.

Also, be aware the black walnut leaves can poison stock, cause asthma in people and horses at the right time of year, and even 10/20% of walnut wood in bedding for stabled horses, can cause founder in 48 hours.  Also warned against using it in bedding for pet mice through rabbits. I had a sheep die from nibbling leaves, and found huge warnings in dept of ag info from America and Canada.  Other walnuts, commercially grown, often have black walnut rootstock. which effect the plants in the spud family, asparagus, etc.  Sorry slight deviation, but wish to save others from distress.In Oz, no one seems aware, but we don't have the huge plantations of commercial walnuts.  I think, due to many commercial walnut farms in California being scrubbed out for redevelopment and grapevines, the walnut shavings/sawdust problem was discovered.