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Japan last week confirmed its first case of variant Creutzfeldt-Jakob disease (vCJD), the human version of mad cow disease, or bovine spongiform encephalopathy (BSE). The disease is said to spread through the consumption of beef products from cows infected with BSE. In Britain, which reported a high incidence of BSE in the 1990s, 148 people have died of vCJD so far. The Japanese case involves a man in his 50s who is believed to have contracted the disease during his stay in Britain in 1989. He died in December.

A further investigation by the health ministry is needed to find out precisely how the man got infected. Consumers can rest assured, though, that there is no risk of infection from eating beef now on the domestic market. This is because all slaughtered cows are tested and all high-risk parts removed under the rules that came into force after the first BSE case was confirmed here in 2001.

Nevertheless the government should provide as much information as possible on the latest outbreak and the safety of beef. The kind of confusion that occurred in 2001 must be prevented. Basically, consumers need not worry, not only because the safety of beef in distribution is guaranteed but also because it is unlikely that new vCJD patients will appear.

CJD is a neurodegenerative disease in which a prion — a microscopic protein particle similar to a virus but lacking nucleic acid — creates spongelike holes in brain tissue. Nonvariant CJD, which is not related to BSE, is said to occur at a rate of about one person in a million. In Japan, about 100 people contract it each year. This type is called “sporadic” CJD because it occurs at random.

Variant CJD is believed to result from eating parts of a BSE-infected cow containing prions — such as brain tissue and spinal cord — or meat that became contaminated with prions at the time of slaughter. This variant type, unlike the sporadic one, is said to occur mostly in younger people.

The origin of BSE is attributed to scrapie, a prion disease that produces a spongiform pattern in the brains of sheep. Research shows that prions in infected sheep were transmitted to cows first through meat-and-bone meal prepared from waste parts of those sheep, and that some of the prions then found their way into other cows through similar feed produced from the waste parts of infected cows. In Britain, BSE is said to have spread in this fashion, affecting more than 180,000 cattle.

It is believed that BSE cases in Europe and Japan originated with meat-and-bone meal imported from Britain before safety measures were put in place.

The incidence of BSE in Britain reached a particularly high level around 1990. After a period of incubation, human cases began being reported in the mid-1990s. It is difficult to estimate how many people will contract vCJD in coming years. Some specialists put the number at anywhere between several hundred and several thousand. Others say the toll in Britain could exceed 130,000 if worse comes to worst.

Given these developments, there had been concern in Japan that some of the Japanese who resided in Britain around that time might develop vCJD symptoms. Last week’s announcement seems to have confirmed that concern.

On the other hand, there is very little possibility of vCJD infection spreading from beef distributed in Japan. The possibility of human infection from previously imported beef is almost zero, according to a report published in September by the government’s Committee on Food Safety. The health ministry emphasizes that there is no cause to be concerned about human-to-human infection, be it sporadic or variant. The only known case, it says, was one caused by transplantation of dura mater (the outer membrane covering the brain) from an infected person.

The confirmation of Japan’s first case of vCJD may or may not affect Japan-U.S. talks on resuming imports of American beef. But basically the incident has nothing to do with the import issue. The report by the food safety panel says it is difficult to detect BSE in cows younger than 20 months. On that basis, the health and agriculture ministries are reviewing the 2001 rules for blanket testing. The United States, whose beef exports to Japan have been suspended since a BSE case was confirmed there in December 2003, is calling for a resumption of beef exports for cows younger than 17 months. The key question is whether the U.S. can scientifically convince Japanese consumers about the safety of its beef.

The government, meanwhile, should provide accurate information on both BSE and vCJD, and set clear-cut safety standards for beef. Only by doing so can it prevent confusion among consumers and build confidence in its food administration.

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