Pigs are seen in a piggery at a village near Warsaw April 10, 2014. REUTERS/Kacper Pempel

CHICAGO (Reuters) - The United States suspended imports of pork from Poland on Thursday over an outbreak of the highly contagious hog disease African swine fever in that country.

African swine fever has spread rapidly in eastern Europe and China, the world’s largest pork producer, where new cases are appearing and the disease is traveling far distances.

The United States is free of the disease, and anxious to keep it that way because infections in U.S. herds would likely kill hogs and limit pork exports.

Humans are not susceptible to African swine fever, according to the USDA.

The agency said it was reviewing Poland’s export protocols after finding one facility there shipped pork to the United States without following requirements designed to prevent the spread of serious livestock diseases. A second Polish facility is also being reviewed, according to a USDA notice.

The USDA is also working with Customs and Border Protection staff to enhance screening of passenger bags coming from Poland, the notice said. The checks aim to ensure restricted products are not brought into the country.