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Professor John Collinge
"The average incubation in kuru is 12 years"
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Friday, 23 March, 2001, 12:18 GMT
Cannibalism's clues to CJD

Nobody knows how many will be killed by the human form of mad cow disease. But a similar disorder among cannibals in Papua New Guinea gives some important clues.

Ever since a link was established between mad cow disease and its human form, variant CJD, a time bomb has been ticking.

Because the fatal vCJD takes years to emerge in humans, the number of new cases is rising all the time.

Mad cow
Mad cow disease and vCJD are both "spongy-brain diseases"
But experts are stumped when it comes to estimating the total number of deaths. Suggestions have ranged from millions to a few hundred.

The problem is that so much about the human form of mad cow disease continues to mystify experts.

Yet the case of a similar disease among a tribe of cannibals from Papua New Guinea is proving an unlikely source of enlightenment to scientists.

Like vCJD, kuru is a fatal spongy-brain disease, known to doctors as a transmissible spongiform encephalopathies.

Likely death toll from vCJD
Report in 2000 estimated between 14,000 and 500,000
Source: Wellcome Trust Centre for the Epidemiology of Infectious Disease
The condition was first noticed by western scientists in the 1950s among members of the Fore tribe, based in the jungle highlands of Papua New Guinea.

Symptoms start with pains in the joints and headaches, and progress to loss of co-ordination, tremor, uncontrollable laughing and dementia.

Victims are said to become progressively paralysed, with frozen, masklike smiles on their faces. The disease progresses steadily and death occurs within two years.

By the time kuru, which means "trembling" or "shivering", was discovered by outsiders, it was killing half of all women and children in the Fore tribe.

Donnamarie McGivern
Donnamarie McGivern is among 85 people to have died from vCJD
Initially, scientists thought the illness was hereditary since it carried none of the classic symptoms of infection - fever, inflammation, changes in white blood cells and antibody response.

Additionally, while most bacterial or viral diseases produce illness within days or months, kuru seemed to take years to develop.

But the American physician Dr Carleton Gajdusek had a hunch the disease might somehow be related to the tribe's eating habits. Fore men supplemented their bean-and-sweet-potato diets with small game, but women and children lacked protein.

To make up for this, the women had recently started a ritual of eating the brains of tribal members who had recently died.

Sponge-like holes

Autopsies revealed the brains of those who died from kuru contained small cavities like the holes in a sponge. To Dr Gajdusek it looked like the effects of Creutzfeldt-Jakob disease (CJD), the disease which is related to vCJD but which strikes randomly and infrequently all over the world.

Where these diseases jump from one species to another incubation periods are much larger

Professor John Collinge
He experimented by injecting the crushed-up brains of kuru victims into chimpanzees. After two years the apes showed signs of kuru.

Dr Gajdusek deduced that the illness was caused by an infectious agent called a prion. His work earned him the Nobel Prize for medicine in 1976.

The findings have helped scientists working in the field of vCJD determine incubation periods, says Professor John Collinge who sits on a panel of experts which advises the government on CJD.

"The [CJD] cases we are seeing at the moment are, by definition, those with the shortest incubation period," says Mr Collinge.

In the small village of Queniborough, five have already died of vCJD
"The average incubation period in kuru is thought to be around 12 years. There the transmission is from human to human. But where these diseases jump from one species to another we know that they are associated with much larger incubation periods."

But even though the Fore tribe called a halt to cannibalism in 1957 the death toll, which currently stands at more than 2,500, has not stopped altogether. Elderly members are still dying of kuru.

This has led doctors to suggest that the average incubation period for the human form of mad cow disease could be a lot longer than originally thought. Mr Collinge says it could be 30 years.

Gene variations

Crucially, it seems that the length of incubation may be due to individuals' gene makeup.

People are divided into three "geotypes" called M-M, V-V and M-V which occur respectively in 37%, 12% and 51% of the population.

Since everybody who has so far developed vCJD belonged to the M-M combination, it was initially thought that others may have a genetic immunity to the disease.

But, according to Professor Collinge, the 11 newest cases of kuru, have affected those with the M-V geotype. His fear is that vCJD may run a similar course - showing initially in one geotype and developing later in another.

It means the British people must live with the threat for many years of being struck down by a disease that could kill almost one in a hundred of us.

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See also:

22 Mar 01 | Health
'vCJD may take 30 years to show'
19 Jan 00 | Health
CJD 'will not be an epidemic'
18 Aug 99 | Medical notes
Prion diseases
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