Scientists have yet to document a single U.S. case of someone getting the human version of mad cow disease from contaminated beef. Then again, they might not be looking hard enough.
Some experts say scientists should be looking more closely at cases of Creutzfeldt-Jakob disease (search) — a brain-destroying disorder that kills hundreds of Americans each year — to see whether some of these deaths were, in fact, caused by beef from cattle infected with mad cow disease.
"Could there be one [missed] case in there? Maybe," said Lawrence Schonberger, a Centers for Disease Control and Prevention (search) epidemiologist who has studied CJD for more than a decade. "In this game, we never say something's impossible."
CJD comes in two known varieties: variant CJD, which is caused by eating tainted beef, and classic CJD. In classic CJD, the source is unknown in about 85 percent of cases, but doctors generally believe beef is not the cause. The other classic CJD cases are blamed on an inherited genetic mutation or use of contaminated instruments or tissue in surgery.
According to government estimates, CJD accounts for about 300 deaths a year in the United States — all of them believed to be of the classic variety.
But autopsies are performed in only about half those cases. So it is possible that cases of CJD from eating tainted beef have been missed, experts say.
Schonberger and Dr. Pierluigi Gambetti, head of the top U.S. lab studying CJD and similar diseases, said they hope the mad cow scare that broke out late last month with the discovery of an infected cow in Washington state will lead to more autopsies on people with CJD.
"I think everyone needs to make a better effort to really gauge the incidence in the United States and not to miss variant or any other form," said Gambetti, director of the National Prion Disease Pathology Surveillance Center (search) at Case Western Reserve University in Ohio.
In both forms of CJD, mutant proteins called prions eat holes in the brain, but microscopic examination of brain tissue shows distinct differences between the two.
Classic CJD normally strikes people 55 or older, while variant CJD typically kills people in their 20s and 30s.
Classic CJD incubates silently for years, then usually kills within six months of first symptoms: trouble standing or walking, speech abnormalities and declining mental ability.
In variant CJD, death typically comes about 14 months after the first symptoms. Early symptoms include depression, withdrawal and anxiety, and pain, tingling or numbness. Eventually, patients cannot move or speak.
Only about 150 deaths from variant CJD — most of them in Britain — have been counted worldwide since 1996.
In New Jersey, one woman is pressing health authorities to take a closer look at as many as seven CJD deaths among people who ate at the Garden State Park racetrack in Cherry Hill in the late 1980s and 1990s.
Janet Skarbek, a Cinnaminson accountant, said she is convinced the deaths must be linked to food, even though six of those cases were ruled classic CJD and an autopsy on the seventh victim was inconclusive.
Skarbek began following such cases after a woman in the accounting department at the track where her mother worked died of CJD in 2000 at just 29.
Five months later, Skarbek spotted the obituary of an 83-year-old season pass holder who ate at the track restaurant frequently. Then Skarbek learned a track patron died of classic CJD in 1997. Through October 2003, Skarbek said, four more people died of CJD: three former patrons and a 56-year-old woman from the marketing department at the track, which closed in 2001.
Skarbek said she is not disputing that the seven cases are classic CJD, sometimes called sporadic CJD.
"I'm arguing with the finding that sporadic is not caused by eating tainted beef," Skarbek said Wednesday, noting British scientists initially said that mad cow disease could not be transmitted to humans.
The CDC's Schonberger said Skarbek's theory is unproven but not impossible. One British study in mice suggested mad cow disease might cause classic CJD.
Dr. Omar Bagasra, professor of biology at Claflin University in Orangeburg, S.C., studied brain tissue from the 29-year-old track employee and said the type of damage indicates she might have died of yet a new variant of CJD — perhaps one caused by food.
"CDC needs to investigate this" further, Bagasra said.