Animal Diseases passed on to humans?

How come so many dangerous diseases are passed from animal to human?
Such as the HIV (AIDS), wasn't it first passed on from a chimpanzee when scientists were experimenting with it?
And right, now the Swine Flu.

Most animals have an HIV equivalent. It most likely happened when people were receiving transfusions of equine plasma. It was a common procedure 50 years ago, but since went out. The virus likely just adapted to the new human environment. It does mutate quickly, after all.

Any way, the reason it's so dangerous when they cross species is because we have no natural immunity to it. Over time the virus will be less dangerous.

Swine flu is a combination of a mutated strain of Pig flu viruses and Human flu viruses.It just happens when two viruses replicate. Nothings targeting us over another species of animal. (We're not that special).

YOU CANNOT GET THE FLU FROM A PIG OR FROM EATING PORK< THIS IS NOTHING LIKE HIV STOP FREAKING OUT.

in the case of HIV, someone most likely ate infected monkey meat and the strain was able to works itself into the system

Sorry for the caps, I like using them

Most virus's get passed to human from animal after the virus mutates to be able to have human as a host. It gets passed through some type of liquid transfer as through water, water droplets from the lungs or respiration's from the infected animal or blood, feces,etc,.,

There is no evidence to show that swine influenza can be transmitted through food to the humans.However eating properly handled and cooked pork and pork products is safe. Cooking pork to an internal temperature of 160掳F kills bacteria and viruses.

Well, because they are animal diseases, our bodies aren't prepared to fight them. It seems viruses undergo an evolutionary process where they can mutate from animals to humans. And they say humans mutated from animals, too... so it just seems to be how evolution works.