South Korea has culled more than 11,000 ducks as a preventive measure against the bird flu.

According to the Ministry for Agriculture, Food and Rural Affairs, some of the ducks at a poultry farm in the northwestern city of Incheon had tested positive for a virulent strain of the bird flu this past Saturday.

The ministry added that in order to prevent avian influenza from spreading, all 11,604 ducks were slaughtered. The farm has also been placed under quarantine. The strain was identified as H5N8, which is a subtype of the influenza A virus that is not as pathogenic as the H1N1.

The strain was confirmed at the farm after the Animal and Plant Quarantine Agency and a livestock research center in the region conducted an investigation when the farm reported that dozens of their ducklings had mysteriously died.

Since the confirmation, the ministry has issued an order banning all poultry and eggs from leaving any farms in the Gyeonggi Province. The order will last through April 2. On top of this measure, the city also created two disease monitoring posts that will be responsible for disinfecting all vehicles that enter and leave the city. The posts will remain until health officials can determine that there is no transmission risk involved.

The North Chungcheong Province also set up similar posts, while Jeju Island is prohibiting the entry of any poultry, eggs and birds coming from the Gyenoggi Province, Seoul and Incheon.

The last time that South Korea had a confirmed case of the bird flu was in Nov. 2015. The strain involved was also the H5N8. An infection typically leads to respiratory flu-like symptoms, such as headache, coughing and fever. Although there are symptoms, confirming an infection requires laboratory tests.

"Avian influenza A virus infection in humans cannot be diagnosed by clinical signs and symptoms alone - laboratory testing is required," the Centers for Disease Control and Prevention (CDC) said. "Avian influenza A virus infection is usually diagnosed by collecting a swab from the nose or throat of the sick person during the first few days of illness. This specimen is sent to a lab; the laboratory looks for avian influenza A virus either by using a molecular test, by trying to grow the virus, or both."

News of the bird flu came shortly after the country dealt with an outbreak of foot and mouth disease (FMD) that affected pigs from a farm in Gimje in January.