An additional case of bird flu was reported at duck farms in South Korea, the second case in one week, raising concerns that avian influenza (AI) may have spread to other parts of the country.Tests showed that ducks at the two poultry farms in Buan, 280 kilometers south of Seoul, were infected with AI, but it was unclear whether it is the highly pathogenic strain, the agriculture ministry said. The final test results are expected later in the day at the earliest, according to the ministry.On Friday, South Korea confirmed the outbreak of the highly pathogenic strain of H5N8 in Gochang, 296 kilometers south of Seoul, the first outbreak of AI since May 2011. It culled some 21,000 birds at the farm.South Korea is stepping up quarantine measures to stop the spread of bird flu. The quarantine authority has launched an investigation into the possibility that the deadly animal virus might have been caused by migratory birds, and the government has issued an order in South and North Jeolla provinces to temporarily prevent poultry, livestock raisers and their vehicles from leaving the areas on Sunday and Monday, according to (Yonhap) news agency.Prior to the latest series of outbreaks, South Korea was hit by AI four times, with the last cases occurring in 2011 that led to more than 3 million poultry being slaughtered. In 2008, the government slaughtered 3.45 million birds because of the virus, at a cost of around 32 billion won (US$28.4 million). Other outbreaks took place in the winter months of 2003-4 and 2006-7.