BSE infection from young cattle to mice not confirmed
05/09/2007
The Asahi Shimbun
Experiments on mice showed that mad cow disease in two cattle aged 21 and 23 months old was not contagious, a finding that could change attitudes about food safety.
The results of the tests, contained in an interim report compiled by a health ministry-commissioned research group, might lead to a conclusion that humans can safely eat meat from cattle up to 23 months old, even if they were infected with bovine spongiform encephalopathy (BSE), or mad cow disease.
The latest finding could also influence Japan's conditions on beef imports from the United States. Japan currently limits U.S. beef imports to cattle 20 months old or younger when slaughtered.
"If the infection cannot be confirmed through the experiments between mice, then it would be difficult to verify the infectiousness (of BSE)," an expert said.
The research group, headed by Tetsutaro Sata, chief of the Department of Pathology at the National Institute of Infectious Diseases, is now compiling a detailed academic paper based on the findings.
The Ministry of Health, Labor and Welfare is also preparing to report the study to the Cabinet Office's Food Safety Commission, according to sources.
The 23-month-old cow was born in October 2001 and processed at a plant in Ibaraki Prefecture in October 2003, according to the researchers. The 21-month-old cow was born in January 2002 and processed in Hiroshima Prefecture in November 2003.
Both cows were confirmed as infected with BSE when they were processed. It is rare for cattle that young to have BSE.
Cattle are confirmed to be contaminated with BSE if an abnormal prion protein, the substance that triggers the disease, is detected in the animals.
The young cattle had only between 1/500 and 1/1000 of the amount of prion protein found in other BSE-infected cows, so the research group conducted experiments at the National Institute of Animal Health in Tsukuba, Ibaraki Prefecture, to see if the prion protein was infectious.
The group injected fluid taken from the brains of the two cows into the brains of mice that were genetically modified to make them more susceptible to the disease.
Under ordinary circumstances, the mice would develop abnormalities in about 220 days.
But reports and other information obtained by The Asahi Shimbun showed that five mice injected with the brain fluid of the 23-month-old cow survived 600 to 860 days. Six mice injected with the fluid from the 21-month-old cow lived for 505 to 927 days.
Not one of the mice was confirmed as being infected with BSE.
The researchers also injected brain fluid from mice used in the earlier experiments into the brains of other mice to double check the infectiousness of the disease in the young cattle.
The second set of mice injected with brain fluid showed no signs of BSE contamination after at least 495 days.
BSE is more easily passed on from mouse to mouse than from cow to mouse.
The first BSE-contaminated cow in the United States was confirmed in December 2003, prompting Japan to ban U.S. beef imports.
In negotiations for the resumption of the imports, Washington called on Tokyo to adopt international standards set by the World Organization for Animal Health, which says boneless meat from cattle aged 30 months or younger are safe.
But Japan argued that the restriction should be applied to cattle as young as 20 months because of the two young cows confirmed with BSE in Japan. The United States eventually accepted Japan's argument and reached an agreement.
"From the perspective of food safety, I think that the decision at the time to declare the cows as infected with BSE and to exclude meat (from cattle aged 20 months or older) from the market was not wrong," said Takashi Yokoyama, chief of the Research Center for Prion Diseases at the National Institute of Animal Health who was in charge of the experiments. "That decision is totally unrelated to the latest experiments."
Still, Kiyotoshi Kaneko, professor of physiology at Tokyo Medical University, said the results do not provide a 100-percent guarantee of the safety of beef.
"I think that rather than saying that BSE was not infectious, it is more appropriate to say that the amount of abnormal prion protein was very small, and it did not effectively multiply in the mice," Kaneko said. "It is reasonable to assume that there is not much of a risk to human health, but I wonder how far we can generalize the results of the experiments to humans." (IHT/Asahi: May 9,2007)
05/09/2007
The Asahi Shimbun
Experiments on mice showed that mad cow disease in two cattle aged 21 and 23 months old was not contagious, a finding that could change attitudes about food safety.
The results of the tests, contained in an interim report compiled by a health ministry-commissioned research group, might lead to a conclusion that humans can safely eat meat from cattle up to 23 months old, even if they were infected with bovine spongiform encephalopathy (BSE), or mad cow disease.
The latest finding could also influence Japan's conditions on beef imports from the United States. Japan currently limits U.S. beef imports to cattle 20 months old or younger when slaughtered.
"If the infection cannot be confirmed through the experiments between mice, then it would be difficult to verify the infectiousness (of BSE)," an expert said.
The research group, headed by Tetsutaro Sata, chief of the Department of Pathology at the National Institute of Infectious Diseases, is now compiling a detailed academic paper based on the findings.
The Ministry of Health, Labor and Welfare is also preparing to report the study to the Cabinet Office's Food Safety Commission, according to sources.
The 23-month-old cow was born in October 2001 and processed at a plant in Ibaraki Prefecture in October 2003, according to the researchers. The 21-month-old cow was born in January 2002 and processed in Hiroshima Prefecture in November 2003.
Both cows were confirmed as infected with BSE when they were processed. It is rare for cattle that young to have BSE.
Cattle are confirmed to be contaminated with BSE if an abnormal prion protein, the substance that triggers the disease, is detected in the animals.
The young cattle had only between 1/500 and 1/1000 of the amount of prion protein found in other BSE-infected cows, so the research group conducted experiments at the National Institute of Animal Health in Tsukuba, Ibaraki Prefecture, to see if the prion protein was infectious.
The group injected fluid taken from the brains of the two cows into the brains of mice that were genetically modified to make them more susceptible to the disease.
Under ordinary circumstances, the mice would develop abnormalities in about 220 days.
But reports and other information obtained by The Asahi Shimbun showed that five mice injected with the brain fluid of the 23-month-old cow survived 600 to 860 days. Six mice injected with the fluid from the 21-month-old cow lived for 505 to 927 days.
Not one of the mice was confirmed as being infected with BSE.
The researchers also injected brain fluid from mice used in the earlier experiments into the brains of other mice to double check the infectiousness of the disease in the young cattle.
The second set of mice injected with brain fluid showed no signs of BSE contamination after at least 495 days.
BSE is more easily passed on from mouse to mouse than from cow to mouse.
The first BSE-contaminated cow in the United States was confirmed in December 2003, prompting Japan to ban U.S. beef imports.
In negotiations for the resumption of the imports, Washington called on Tokyo to adopt international standards set by the World Organization for Animal Health, which says boneless meat from cattle aged 30 months or younger are safe.
But Japan argued that the restriction should be applied to cattle as young as 20 months because of the two young cows confirmed with BSE in Japan. The United States eventually accepted Japan's argument and reached an agreement.
"From the perspective of food safety, I think that the decision at the time to declare the cows as infected with BSE and to exclude meat (from cattle aged 20 months or older) from the market was not wrong," said Takashi Yokoyama, chief of the Research Center for Prion Diseases at the National Institute of Animal Health who was in charge of the experiments. "That decision is totally unrelated to the latest experiments."
Still, Kiyotoshi Kaneko, professor of physiology at Tokyo Medical University, said the results do not provide a 100-percent guarantee of the safety of beef.
"I think that rather than saying that BSE was not infectious, it is more appropriate to say that the amount of abnormal prion protein was very small, and it did not effectively multiply in the mice," Kaneko said. "It is reasonable to assume that there is not much of a risk to human health, but I wonder how far we can generalize the results of the experiments to humans." (IHT/Asahi: May 9,2007)