A Holstein bull slaughtered in Ibaraki Prefecture last month was confirmed Monday to have been infected with mad cow disease.

The 23-month-old bull is the eighth case of the brain-wasting illness found in Japan and is believed to be the world’s youngest carrier of the disease also known as bovine spongiform encephalopathy, according to the Health, Labor and Welfare Ministry.

The bull was brought to the slaughterhouse Sept. 29; two separate sets of tests carried out by Ibaraki health officials and the National Institute of Infectious Diseases raised concerns about possible mad cow contamination.

On Monday evening, a panel of experts at the health ministry positively diagnosed the bull as having the disease.

It also said the abnormal prions found in the bull were of a different type from those of any of the mad cow infection cases reported worldwide so far.

The bull was born in October 2001 and was younger than the seven beasts previously diagnosed with mad cow disease, the latest of which was confirmed in late January. Until now, the youngest infected cow here was 64 months old.

Since May 2002, the animal had lived at a farm in Katsurao, Fukushima Prefecture. It was previously kept on a farm in Otawara, Tochigi Prefecture, though it was not immediately clear whether the bull was born there.

Prions — protein particles lacking nucleic acid that are suspected of transmitting the malady — are believed to accumulate mainly in older cattle.

Cows examined in Europe for the disease are generally older than 24 months.

Mad cow disease is believed to be caused by the consumption of meat-and-bone meal contaminated with abnormal prions. It has been linked to nervous system illnesses such as Creutzfeldt-Jakob disease.

Japan’s first case was confirmed in September 2001 in Chiba Prefecture. The other cases turned up in Hokkaido, Gunma, Kanagawa and Wakayama prefectures.

Last month, a panel of the Agriculture, Forestry and Fisheries Ministry said the source of the outbreak in Japan was either cows imported from Britain in the 1980s or Italian-made meat-and-bone meal imported before 1990, noting they caused secondary infections through domestic cattle.

The panel had been probing the infection route since last November but was unable to determine which of the two sources was responsible.

It said there could be over 30 additional animals in Japan with mad cow disease, which first broke out in 1986 in Britain.

The fact that the bull, which was born after the first domestic case came to light, was confirmed as having the disease indicates that there may be another route of contamination, experts said.

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