Japanese health experts had previously asserted the high standards of cleanliness in Japanese cattle ranches would keep the country free of the brain-wasting disease, which has ravaged herds in Britain and elsewhere in Europe and is believed linked to a fatal human disease.
But officials were alarmed last month when a cow in Shiroi in Chiba prefecture mysteriously lost the ability to stand. The animal was slaughtered and tests of its brain indicate signs of the illness, according to a statement issued Monday by the Ministry ofAgriculture.
"We must now ask ourselves if our previous way of thinking was wrong, if there were factors we hadn't foreseen," said Kiyoshi Onodera, deputy division chief at the Ministry of Agriculture's animal health division.
The government said more tests were necessary to determine conclusively whether the cow was infected with the disease. This first test was negative but, because it revealed air pockets in the cow's brain, further testing was carried out on September 6. The results on Monday showed that this second test had come in positive for mad cow disease.
Milk produced by the 5-year-old Holstein had already been sold on the market before the slaughter, but scientists believe milk is unlikely to spread the disease. Norio Tsuruoka, an official at the Chiba prefectural office's stockbreeding sanitation section, said about 4,160 gallons of milk from the suspect cow were sold.
He said it was not immediately clear where the milk had been marketed. However, Chiba is a main supplier of agricultural products to Tokyo, which borders it on the west. The cow was destroyed and its meat was not sold.
Some 30 other cows were being bred at the same farm as the suspect cow and there are about 100 cattle in Shiroi in total - but the other animals are not thought to carry the disease, said Tsuruoka. Many have been quarantined, but officials have not yet decided whether to slaughter them.
Scientists believe mad cow disease of bovine spongiform encephalopathy is transmitted through infected meat-and-bone meal fed to cattle and that it may cause the brain-wasting new variant Creutzfeldt-Jakob Disease in humans, which has killed around 100 people in Britain.
Japan started in April to check for BSE in cattle that showed abnormal symptoms before they died.
The incubation period for mad cow disease is believed to be between two and eight years after infection.
The suspect Holstein is believed to have been infected by feed that contained contaminated animal parts, said Katsuaki Sugiura, another official at the Ministry of Agriculture's animal health division.
If confirmed, the case would be the first in Asia. World Health Organization officials said in December they were concerned that BSE-infected animal feed may have been sold arounthe world.
While most imported feed used in Japan comes from the United States, Canada and Australia - all believed to be free of mad cow disease - some shipments were imported from European countries, including Denmark and Italy, before a ban on European feed took effect this year, Sugiura said.
Japan last year banned EU beef and food made from processed beef and bull sperm, which is used for breeding.
Japan has also restricted blood donations from people who lived in Britain - where more than 100 cases of variant CJD have been discovered - since 1980. Mad cow disease was diagnosed in 1986 there and has resulted in wholesale herd slaughtering, mandatory testing and a European Union ban on British beef exports that has since been lifted. Thousands of cattle in Europe have been infected with mad cow disease, most in Britain, and hundreds of thousands of cattle have been destroyed.
A panel of experts was to be convened on Tuesday to decide what further tests were necessary. The government was considering asking British and Swiss experts to help in the investigation, according to the Ministry of Agriculture statement.
It was too early to say when the next test results would be available, said Tsuruoka.
Grain traders were alarmed by the farm ministry's announcement.
"Even if the suspected case came from a dairy cow, dairy cows are used for processed beef products, such as corned beef, after being slaughtered," one trader said.
"Japanese consumers are increasingly conscious about food safety and this suspected mad cow case in Japan will hurt confidence in the safety of beef, both Japanese and imported beef," he added.
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