TOKYO, Feb. 6 (Xinhua) -- The swine flu epidemic continued to spread rampantly in central and western Japan, with local authorities struggling to contain the highly-contagious virus, while the government remained reluctant to use vaccines to eradicate the problem.

Swine flu, also known as hog cholera, was first detected on farms in Gifu Prefecture in September, but has been newly detected in pigs at farms in neighboring Aichi Prefecture, as well as at farms in Osaka, Shiga and Nagano prefectures, authorities said.

They said the number of pigs to be culled and buried at affected farms is expected to reach around 15,000.

"We are facing an extremely serious situation," farm minister Takamori Yoshikawa said at his ministry in Tokyo. He instructed officials to take necessary countermeasures and underscore efforts in Gifu Prefecture to contain the virus.

A vaccine that could counter the hog cholera epidemic here and bring it under control has been snubbed by the government, however, with Yasuhiro Ozato, senior vice farm minister, expressing concern about using the vaccine.

"We will seek to resolve this by sticking to hygiene control standards," said Ozato, who was concerned that using the vaccine would hinder Japan from regaining its World Organization for Animal Health status and being able to expand its pork exports.

Ozato was intimating that if the vaccine were to be used, then Japan would fail to regain its status as a Classic Swine Fever (CSF) free country, which would severely hamper the nation's pork industry.

Up until recently, Japan has had no infections of pig cholera recorded since the first outbreak in 1992, with the virus being declared eradicated in 2007.

The local government in Aichi Prefecture, meanwhile, begun the process of culling around 6,600 pigs at a farm in Toyota City, with local authorities enlisting the help of Ground Self-Defense Force (GSDF) troops.

According to the local Aichi government, despite pigs on the farm in Toyota displaying clear symptoms of the virus, it continued to transfer pigs to a farm in Nagano Prefecture on Tuesday.

The Nagano prefectural government said that of the 80 pigs that were shipped from Aichi, 79 were found to have been infected with the highly-contagious virus.

At the end of January, a farm in Gifu Prefecture, central Japan, was the latest to confirm the presence of swine flu and the continuation of the epidemic in the region, but seemingly failed to contain the outbreak from becoming rampant across five prefectures across Japan.

Prefectural authorities in Gifu had to enlist the help of GSDF troops to carry out an initial 1,600-pig cull and to bury the carcasses.

In December, GSDF troops helped officials in Gifu cull 8,000 pigs, following the sixth positive case of swine flu being detected in Seki, also in Gifu prefecture. The number of positive cases since then has almost doubled, according to the government's latest figures.

Unless the epidemic is eradicated, Japan will not be able to export pork products to the European Union under a new trade pact that has come into effect, Yoshikawa said recently.

The local government in Gifu had suggested the virus may have made its way onto the farm by way of wild boars or pigs that had contracted the disease and had been brought onto the farm.

Shipment of pigs from facilities within a 10-km radius of the infected farm were prohibited to prevent the virus from spreading and five disinfection zones were initially set up to clean vehicles that carry livestock in the area.

These were among other early, government-mandated emergency measures to curtail the spread of the virus from Gifu.