Japan's swine fever epidemic is spreading, with local authorities in five central and western prefectures saying Wednesday they are struggling to contain the highly contagious virus that was first reported in September.

"We are facing an extremely serious situation," farm minister Takamori Yoshikawa told a meeting at his ministry in Tokyo while instructing officials to take thorough countermeasures. The ministry also set up a special task force in Gifu Prefecture to step up containment efforts.

Spreading from farms in Gifu, the hog cholera virus was newly detected by prefectural and local authorities at farms in neighboring Aichi as well as in Osaka, Shiga and Nagano prefectures.

The total number of pigs to be culled at affected farms is expected to reach 15,000.

"It worries me that we don't know how the disease is spreading," said a pig farmer in Iida, Nagano Prefecture. "The only thing we can do is to thoroughly manage hygiene."

The disease does not affect humans even if meat from an infected animal is consumed, but it is fatal to pigs and boars.

Around 130 wild boars in Gifu and Aichi prefecture have tested positive for infection despite experts' initial assumption that it would not spread among the animals, which typically do not live in large herds.

Although there is a vaccine to counter classic swine fever, using it could prevent Japan from regaining its World Organization for Animal Health status as a CSF free country, hindering Japan's plan to expand pork exports. The organization already suspended Japan's such status after the outbreak in September.

Yasuhiro Ozato, a senior vice farm minister, expressed reluctance to use the vaccine, saying, "We will seek to resolve this by sticking to hygiene control standards."

The Aichi prefectural government began culling around 6,600 pigs at a farm in the city of Toyota with the help of the Ground Self-Defense Force, while banning shipments from six other farms located within 10 kilometers.