Re: Why don't dogs get sick from humans.

Hi Stoddy --

Good question! Many illnesses are caused by microorganims which include bacteria and viruses. In many cases these pathogens (organisms that cause disease) produce factors that help them colonize and infect a host animal - you, me, a cow or a dog. Superficially we look different from dogs. When you observe things more closely, you'll find that we differ in many other ways that are too small to be seen by the naked eye. The surfaces of our cell membranes, though similar in many respects, have many differences. Nearly all pathogens need to bind to cell membranes at some point so they can establish a "residence", or worse, get inside the cell to do some damage - bad for us, but good for the pathogen as the inside of a cell has a lot of food and nutrients.

So - the "hook" a pathogen uses to bind to a dog cell's membrane may not work on a human cell, and vice versa.

However, humans can get sick from dogs, and dogs from humans. You may have heard of rabies - a deadly infection that once killed many peple, until Louis Pasteur developed a vaccine against the infection. The virus which causes rabies slowly destroys the nervous system. Infected animals behave oddly, often loosing their fear of humans. For this reason, you should never pet or approach a wild animal that suddenly seems 'friendly.' Dogs infected with the viruses are often called "MAD" as they foam profusely at the mouth, like a madman. The destruction of their nervous system makes it difficult to swallow saliva, so it drools from the mouth. If bitten by a mad dog, a human can contract rabies. Theoretically an infected human could pass the virus to an unifected dog, though I have never heard of it happeneing. In most cases domesticated pets acquire the virus through contact with animals in the wild.

- Lynn Bry, MadSci Admin