Why is it “swine flu” and not “pig flu”?

Nouns

Swine flu has been in the news a lot recently.

This has made me ask three questions: 1. What exactly does “swine” mean? 2. How is “swine” related to “pig”? 3. Why is this flu called “swine flu” and not “pig flu”?

Dictionary.com says that the noun “swine” means any stout, cloven-hoofed artiodactyl of the Old World family Suidae, having a thick hide sparsely covered with coarse hair, a disklike snout, and an often short, tasseled tail: now of worldwide distribution and hunted or raised for its meat and other products..

And Dictionary.com says that the first three meanings of the noun “pig” are (a) a young swine of either sex, esp. a domestic hog, Sus scrofa, weighing less than 120 lb. (220 kg.), (b) any wild or domestic swine, and (c) the flesh of swine; pork.

So swine flu just as easily could be called “pig flu” instead. However, given the third definition of the noun “pig”, and given the claim that this flu does not come from eating pork, it makes more sense to call this “swine flu” than to call it “pig flu”.