"The sudden onset of symptoms sounds a lot like poison, but how on earth would the pig stay alive long enough for enough poison to reach the meat to pose a problem for humans?
One reason poison bait is restricted here in the US is that other animals die from eating the intestines of poisoned animals, not from eating the meat. You might be able to cross check with someone in animal control or the USDA.
A Google search on "animal control" trapping poison suggests Australia and New Zealand have the most current knowledge of the effects of poison on pigs.
A second problem is the weird distribution. That would have to be the result of humans moving products (such as hog feed or building materials), and I don't think there's all that much of that in China?
Yet the little I've heard does not sound exactly right for a disease, either. Less wrong, but not "right".
Cursed CYA politicians. [*]
I am not sure what you mean by "weird distribution" or "humans moving products." If you're asking how a poison could have traveled so quickly from village to village in Sichuan, I am afraid that's probably not a mystery. Reportedly several of the ill pigs did not die from illness or slaughtering. They died from drowning.
There are accounts that villagers threw sick pigs in rivers. Enterprising villagers downstream fished the drowned pigs from the rivers and sold them at markets, where individual customers and pork processors bought them. See this report for details:
Of course we have to consider the sources in the report. But I think throwing ill livestock in rivers to get rid of them has been done all over the world since anyone can remember, and surely the practice still exists in less developed regions. So I think the gist of the report rings true.
And butchering the pigs would have meant splattering blood. If the pigs were alarmingly sick -- those villagers know enough to fear getting contaminated by blood. It makes sense that many would have simply panicked and thrown the ill pigs in the river.
If so, that's possibly how the illness spread so fast in Sichuan: it floated down rivers.
With regard to your other question, keep in mind that Dr. Wong maintains the onset is not sudden, which pits his medical opinion against several reports. In any case, we don't know how long the pigs stayed alive after being infected (or poisoned). All we know is an anecdotal report that pigs were foaming at the mouth prior to slaughtering.
Other reports seem to suggest that the villagers who slaughtered ill pigs didn't realize the pigs were ill until they got sick from eating the pig meat. That suggests at least some of the ill pigs didn't immediately keel from illness or show obvious symptoms.
As to how poison could travel in the pig's body -- it would be important to take into account the question; however, your question skips a few steps.
First, find every published account of symptoms and circumstances pertaining to the onset in humans and pigs. Only then would it be possible to develop a tentative list of the kind of poison material that could produce the same symptoms.
Only after those preliminary steps would another step be to ask how quickly such poisons could be absorbed into a pig's blood stream and whether they could likely permeate the pig flesh sold for human consumption.
I will observe that there have been reports of villagers thoroughly cooking (i.e., boiling) pig meat from "infected" pigs before eating it and still getting sick. Yet these accounts describe that the same villagers slaughtered the infected pig, which they later boiled and ate. So they could have gotten sick from exposure to contaminated blood, not from consuming the boiled pig flesh.
But such an observation is one factoid in a data puzzle. We can't do anything with the fact; we have nowhere to fit it. So we have to throw it on the piles of factoids and anecdotal accounts, where it will sit until we get hard data.
And we have to hope that US intelligence agencies and the CDC are doing the kind of stepwise investigation I've outlined and keeping an open mind during the process. Because there is another way the "pig disease" could have appeared as if by magic around the same time in different parts of Sichuan.
[*] Pundita's search at Google turned up several possibilities for the CYA acronym. Yet in the context of the reader's observations I think we can safely exclude "Chinese Yacht Association" and settle on the colorful insult.