A fresh case of highly-virulent bird flu was discovered at a poultry farm south of Seoul Thursday for the first time in just a month, government officials said.

The latest outbreak was reported on Feb. 10 in Anseong, about 15 kilometers north of Cheonan where a similar bird flu case was detected in January.

It is the seventh bird flu case since Nov. 25 when the first outbreak was reported on a poultry farm in Iksan, about 230 kilometers south of Seoul, in three years.

Authorities started an investigation into the fresh case Tuesday when a farmer reported that about 30 ducks at the farm died of an unknown cause, a ministry official said, adding that the remaining 13,000 on the farm will be slaughtered.

The official said the quarantine authorities were to cordon off an area within a three-kilometer radius of the duck farm and destroy 55,000 chickens and ducks there.

The Geneva-based World Health Organization believes the virus can mutate into a highly virulent strain that can easily be transmitted among humans if left unchecked.

More than 250 people have been infected by the virus since 2003, of whom at least 161 are believed to have died from the disease, it said.

In 2003 and 2004, South Korea destroyed more than 5 million poultry to curb the spread of the disease. No South Korean has yet to be infected.