^As I recall a lot of the zombie dumping came about after the panic hit India and there were literally MILLIONS of people crowding the coastal docks trying to get the hell out of the "white zone." Imagine how many people you can cram onto just one of those huge bulk freighters if you packed them it tight. In those kind of cramped conditions all it would take is for one person to be able to hide a bite and suddenly the masses of ocean ghouls isn't so surprising.