Human 'Mad Cow' Could Cause Eventual Epidemic

vCJD may have 50-year incubation period, meaning most cases have yet to arise, experts say

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FRIDAY, June 23, 2006 (HealthDay News) -- Variant Creutzfeldt-Jakob disease, the human form of "mad cow disease," has an incubation period of half a century, and could cause an eventual epidemic, British researchers report.

In findings published in the June 24 issue of The Lancet, they looked at a similar disease -- linked to cannibalism -- to better understand the impact such an epidemic might have.

Mad cow disease, or bovine spongiform encephalopathy (BSE), is caused by misfolded brain proteins called prions, which cows contract through contaminated feed. Humans can catch the human form of the disease, vCJD, by eating contaminated beef. So far, the fatal degenerative illness has infected about 160 people in the United Kingdom. More cases have been confirmed in six other countries, including the United States.

Now, researchers at University College London have determined, through the study of a similar disease, that BSE has an incubation period of more than 50 years before it actively becomes vCJD.

Patients in Papua New Guinea with a disease called kuru -- the only currently epidemic human prion disease -- were studied to determine how long the disease was dormant before symptoms appeared.

Kuru occurs in Papua New Guinea society because the disease was transmitted through cannibalism -- a common cultural practice up until 1960. By comparing the birth year in relation to the cessation of cannibalism in the community, the researchers were able to assess incubation periods of the disease.

Eleven participants in the kuru study had minimum incubation periods of between 34 and 41 years, the researchers calculated. They could more accurately calculate the date of infection for men, and estimated an incubation period of between 39 and 56 years, with the potential for seven years longer than that.

The researchers also noted a genetic variation in some kuru patients that has been known to promote long incubation periods.

John Collinge, one of the researchers, said that the current small cohort of vCJD patients "could represent a distinct genetic subpopulation with unusually short incubation periods for BSE," suggesting that many more vCJD patients who caught the disease via contaminated beef could emerge in the coming decades.

"A human BSE epidemic may be multiphasic, and recent estimates of the size of the vCJD epidemic based on uniform genetic susceptibility could be substantial underestimations," Collinge said in a prepared statement.

More information

The U.S. Centers for Disease Control and Prevention has more information on variant Creutzfeldt-Jakob disease.

SOURCES: The Lancet, news release, June 22, 2006

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