CENEI, ROMANIA — For centuries — from the Hapsburg Empire through Communist dictatorship — peasant farmers here have eked a living from hogs, driving horses along ancient pocked roads and whispering ritual prayers on butchering day.

Old customs and jobs are dying and the air itself is changing, however, transformed by an American newcomer, Smithfield Foods. Almost unnoticed by the rest of the Continent, the agribusiness giant has moved into Eastern Europe with the force of a factory engine, assembling networks of farms, breeding pigs on the fast track, and slaughtering them for every bit of meat and muscle that can be squeezed into a sausage.

The upheaval in the hog farm belts of Poland and Romania, the two largest E.U. members in Eastern Europe, ranks among the Continent’s biggest agricultural transformations.

It also offers a window on how a Fortune 500 company based in Virginia operates in far-flung outposts. Smithfield has a joint venture in a Mexican hog farm located near where United Nations scientists are investigating a potential link between pigs and the new strain of influenza in humans. With the exact origins of the virus still in doubt, Smithfield emphasizes that the disease has struck none of its hogs or employees.