Well, I'm assuming they are killing off their pigs because they have confirmed cases of infected pigs or at least have good reason to beleive the pigs are infected. If they don't then I agree that it seems a little strange. As for the other stuff then you are skipping over an entire phase when you say that as soon as a human is infected the pigs are no longer involved. Once the infection jumps to humans it only spreads from pigs to humans initially. This is called the phase 3 outbreak. This type of transmission doesn't stop just because humans now have the virus, the infected pigs didn't sudde