PARIS, Dec 17 (Reuters) - France has detected bird flu on a duck farm in the southwest of the country, the farm ministry said on Friday, marking a return of the disease to the foie gras production region where duck flocks were decimated by outbreaks last winter. The highly pathogenic H5N1 bird flu virus was found in the Gers administrative county on a farm that breeds ducks for foie gras, the liver pate speciality, the ministry said in a statement. All ducks on the affected site as well as flocks on seven other nearby farms would be slaughtered to stem the spread of the virus, it said. Severe forms of avian influenza, commonly called bird flu, have spread in Europe and Asia in recent weeks. In France, eight outbreaks have now occurred on farms, with the previous seven cases in the north, according to the ministry. read more Bird flu is often fatal for poultry. It cannot be transmitted through food although some human cases have raised concern among epidemiologists. France slaughtered more than 3 million ducks a year ago to counter a previous bird flu wave. Bird flu outbreaks can trigger trade restrictions. China has banned imports of French poultry products since late last year. read more