CJD Incubation Period May Well Be Over 60 Years

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Main Category: CJD / vCJD / Mad Cow Disease
Article Date: 23 Jun 2006 - 10:00 PDT

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As the CJD incubation period may be over 60 years, we could be decades away from an epidemic, say researchers from University College London and scientists from Australia and Papua New Guinea. The researchers studied former cannibals in New Guinea where a disease called 'Kuru' exists. Kuru has very similar symptoms to CJD, and like CJD, is caused by a prion.

As BSE-contaminated beef was consumed during the 1990s, the number of humans developing CJD may not be known until we are half way into the present century.

Kuru has an incubation period of 50 to 60 years, the researchers say that the incubation period for BSE, which can infect humans who then develop CJD, could be even longer. This is because CJD comes from cattle, the species-barrier effect could prolong the incubation period.

You can read about this study in The Lancet 2006; 367: 2068-74.

If two million heads of cattle may had been affected in the UK during the 1990s, the number of British people walking around with a CJD timebomb could be enormous. Several other countries also had BSE infected cattle, from many parts of the EU, to the USA, Canada, Japan and Israel.

160 humans have been diagnosed with CJD in the UK since the late 1990s. The CJD prion behaves in a similar way to the Kuru prion. The number of CJD cases in the UK could take a massive hike in the years to come. The researchers said it is impossible to know how high the numbers of human cases will be, or whether the numbers will rise at all, as we have no idea how many people are currently infected. However, if what happened to cases of kuru is anything to go by, it is not possible to say now that the number of humans with vCJD has peaked.

The people of South Fore, Papua New Guinea, used to eat the brains of humans. It was common practice during funerals. This practice was stopped during the 1950s. Some of them developed Kuru - a deadly encephalopathy, just like CJD. Mostly women and children became ill. Males did not usually eat human brains after they were eight years' old. Kuru is a prion disease which is transmitted by eating members of your own family or cultural group (endocannibalism).

The researchers studied the incubation period for Kuru as well as looking into who are/were the most susceptible to the illness. Monitoring started in 1996. During 1996-2004 11 humans with Kuru were identified, seven men and four women - all of them had been born in 1933 - 1949. At the onset of the disease they were aged 46-62.

The investigators used epidemiological and human behavioural evidence to factor out the likelihood of cannibalism being practised after the ban by these 11 infected individuals. They were certain none of them had consumed human brains after 1960. Therefore, we can be certain that the Kuru incubation period is at least 34-41 years. It could be longer as some of the patients were born much earlier than the 1950s.

As men never practised cannibalism after the age of eight, it would be safe to estimate that for men the incubation period could be 39 - 63 years.

The team concluded that the 'Incubation periods of infection with human prions can exceed 50 years. In human infection with BSE prions, species-barrier effects, which are characteristic of cross-species transmission, would be expected to further increase the mean and range of incubation periods, compared with recycling of prions within species. These data should inform attempts to model variant CJD epidemiology.'

Written by: Christian Nordqvist
Editor: Medical News Today
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