March 28, 2002 The Washington Post by David BrownThe number of British cases of the rare and fatal human equivalent of "mad cow disease" is doubling every three years, even though measures to protect meat, the presumed source of the infecting agent, have been in place for nearly a decade.
The continued growth of the epidemic of variant Creutzfeldt-Jakob disease (vCJD) almost certainly reflects the long delay between infection and the appearance of symptoms, rather than representing new infections, a British scientist told a gathering of infectious disease specialists here.
"The trend is continuing upward," said Robert Will, of Western General Hospital, in Edinburgh, Scotland. "The central issue is, how long is this going to go on? We don't know, because we simply don't know what the incubation period is." So far, 117 cases of vCJD have been diagnosed in Britain, five in France, one in Italy and one in Ireland. No cases have been found in the United States, nor has this country had any cases of mad cow disease.
The human disease was identified in March 1996 (although three deaths from 1995 were subsequently ascribed to it). It is characterized by widespread decomposition of brain tissue, giving the organ a sponge-like appearance at the time of death. There is no treatment.
Most victims of "classical" Creutzfeldt-Jakob disease die in their late sixties after developing relatively slow-onset dementia. In the "variant" cases, mortality peaks in the late twenties, and is often preceded by sudden behavior changes initially diagnosed as psychiatric illness.
The cause of both forms of CJD is thought to be an abnormal form of a protein, called a prion. Unlike all other known infectious agents, prions contain no genes, DNA or other genetic material.
Classical CJD can arise spontaneously, or it can be acquired as an infection. Cases have occurred after people have gotten tissue transplants or brain-derived hormones from cadavers whose infections weren't apparent at the time. In the case of vCJD, however, meat is the presumed source. That's because, on the basis of both molecular and organ damage, it appears to be identical to mad cow disease, whose formal name is bovine spongiform encephalopathy (BSE).
BSE was recognized in Britain in the 1980s. It was spread, in part, by feeding cattle with bone and protein supplements that contained brain tissue from infected animals. That practice was stopped in 1988 in Britain. Since then, many countries have taken many measures to keep nerve tissue out of feed and meat.
No risk factors other than age and meat-eating have been implicated, Will told scientists attending the International Conference on Emerging Infectious Diseases. The disease isn't associated with social class, occupation or previous surgery. Men and women are about equally affected. Travel to Britain isn't necessary. Three of the French victims, and the single Italian, had never visited.
The results of one survey of British vCJD patients hinted that victims might have eaten a higher-than-usual amount of hamburgers, sausages, meat pies and other foods made with ground meat. (Ground meat can be inadvertently contaminated with flecks of nervous tissue, other studies have shown.) One theory for why vCJD has such a striking predilection for young adults is that lower-grade ground meat might have been a constituent of school lunches a decade or so ago, Will said. He hastened to add, however, there's no evidence to support that hypothesis.
British epidemiologists have identified 22 people who received blood from vCJD victims and none has the disease or died of it, Will said. Nevertheless, the Food and Drug Administration has asked that blood collecting agencies in the United States not accept blood from people who spent time in Britain in the 1980s.
A team of French researchers reported earlier in the conference that its mathematical model of the British epidemic suggests the time from infection to obvious disease is 14 to 16 years. The model predicts there will be 267 cases, with an upper limit of 672.
Nearly two-dozen European countries have found BSE, including eight last year. The recent discovery of three BSE cases in Japan shows the disease exists outside Europe. A method of assessing a country's risk of having BSE cattle based on its past feed importation practices has proved quite accurate, and Asian countries should now start using it, said Dagmar Heim, of the Swiss Federal Veterinary Office.
CORRECTION-DATE: March 29, 2002
CORRECTION: A March 28 article correctly stated that no cases of variant Creutzfeldt-Jakob disease (vCJD) have been found in the United States. The disease is a rare infection predominantly affecting people in their twenties and is believed to be acquired by eating meat from animals with "mad cow disease." Classical Creutzfeldt-Jakob disease (CJD), which strikes the elderly and has biological properties that distinguish it from vCJD, is found in the United States. From 1979 through 1998, 4,751 cases of CJD were reported here, with only 10 occurring in people under age 30, according to federal government statistics.