January 13, 2004

 

 

Mad Cow Toll In UK Overstated

 

When the mad cow disease first appeared in the United Kingdom back in 1996, scientists predicted that its spread would kill thousands of Britons.

 

Fortunately, extreme predictions of up to 500,000 annual U.K. deaths haven't come to pass. So far, a total of 139 Britons have died of variant Creutzfeldt Jakob disease, or vCJD, the brain-wasting malady linked to the consumption of contaminated beef. Instead of exploding, the number of cases appears to have peaked and could be on the decline. Last year, 18 Britons died from the disease, compared with 17 in 2002 and 28 in 2000, according to statistics recently published by the U.K. Department of Health.

 

While Americans may fret about the appearance of the bovine version of the disease in a single cow, many British consumers -- and scientists -- are less fearful. The most recent calculations by researchers at London's Imperial College, published last year in the journal, BMC Infectious Diseases, suggest that there could be only 40 additional human cases over the next 75 years.

 

"Doomsaysers said that so many people had been exposed to infected beef that mad-cow disease would be Britain's number one health problem," says Christl Donnelly, an epidemiologist at Imperial and one of the authors of the BMC study. "Now it seems that a dramatic increase in cases is unlikely."

 

There's reason to be cautious, though. It isn't clear whether the disease incubates in some people for much longer than in others, which might mean a spurt in cases in coming years. And unlike with HIV, there isn't yet a diagnostic test that would let health officials measure how many Britons may still be incubating the disease, but not yet showing any symptoms.

 

"Compared to what some of us feared, the situation is obviously a lot better than what it could have been," says Peter Smith, head of the U.K. government's scientific advisory committee on bovine spongiform encephalopathy, or BSE, the related affliction that affects cows. "But it's too early to conclude that the end of the disease is in sight," he adds.

 

Just last month, there was news that a British man died from vCJD after he apparently acquired the disease via a blood transfusion from an infected donor -- the first such case. (The donor also died of vCJD.).

 

A decade or more ago, the uncertainty was far greater. Millions of people were potentially exposed by consuming cow brains or other risky material after the disease was found in British cattle, and some scientists warned that the human form of mad-cow disease would have a bigger impact than AIDS and wipe out an entire generation of Britons. Richard Lacey, a scientist at Leeds University in England, rose to prominence after being the first to propose that people contracted vCJD after eating beef from BSE-infected cows. According to a government report on BSE published in 2000, Prof. Lacey noted in a British newspaper that, "in the years to come our hospitals will be filled with thousands of people going slowly and painfully mad before dying." (Prof. Lacey, who is now retired, declined to comment.)

 

What changed? Two measures adopted by the U.K. government are seen, albeit belatedly, as crucial in limiting the damage. To prevent animal-to-human transmission of mad-cow disease, the U.K. government in 1996 banned the most infective portions of a cow -- brain and spinal cord material -- from the food supply. It also banned the use of bonemeal in animal feed. "The key lesson for countries is the importance of the feed ban -- not feeding cows to cows," says Prof. Donnelly. "It's vital that ban is maintained."

 

Although vCJD is still a largely mysterious malady, scientists know more about its provenance and about how it spreads. They now believe that vCJD isn't as infectious as previously thought, and that humans aren't as susceptible to it as some other species. While domestic cats have gotten a feline version of the disease -- probably from cat food containing infected bonemeal -- experiments to orally infect chicken and pigs have not yielded the same result.

 

In humans, the toll may have been limited because of genetic variation. The human form of mad-cow disease, vCJD, is believed to be caused by the misfolded form of a protein known as a prion. While everyone has a gene that codes for prions, there are differences. In the U.K., only those with a particular variation of the gene -- shared by 40% of the population   have contracted vCJD so far. The big question remains: Are there other genes, not yet identified, that might also increase susceptibility to mad-cow disease?

 

For now, the allaying of fears is evident in Britain. The country's McDonald's franchises, Burger Kings and steakhouses are doing brisk business. Beef consumption is at the highest level since the mad-cow crisis began. And in July, the U.K.'s Food Standards Agency recommended that the government lift a ban that prevents cattle older than 30 months from entering the food chain.

 

The ban was ordered because older cows tended to show symptoms of BSE, suggesting a lengthy incubation period. But because of the other measures to make beef safe and the recent decline in human cases, "we now believe that the increased risk from cattle over 30 months is tiny," says a spokesman for the agency. As a precaution, however, the agency has recommended that older cows can be sold as beef provided they test negative for BSE, a practice already followed by other European countries.