From the jungles of Papua New Guinea in the 1950s, through Australian fertility clinics, to the butcher shops of Britain in the 1990s, a creeping epidemic has claimed the lives of thousands of men, women and children.

The Eastern Highlanders of PNG called it kuru – the shivering disease. In the West, we know it as Creutzfeldt-Jakob disease (CJD). To the world’s media, it is now notorious as “mad cow” disease.

All three are among a group of rare human and animal diseases that induce neurological disaster – microscopic holes in the brain, sticky plaques of protein that prevent vital messages between nerve cells – and a plethora of symptoms including staggering, jerking, memory loss, personality change and dementia. Collectively, they are known as transmissible spongiform encephalopathies, or TSEs. A more recent term, “prion” disease, to denote the apparent cause of these diseases by a “proteinaceous infectious particle” in the brain, is also widely used.

Their incidence in humans, sheep, farmed mink, deer and elk and, more recently, in cows, cats and zoo animals, has created a global jigsaw for which the pieces are only gradually coming together. Several theories about the elusive cause of TSEs remain just that – despite two Nobel prizes among the elite group of scientists and researchers battling to identify the disease source.

The biggest TSE killer in humans is CJD, first identified in the 1920s by German neuropsychiatrists Hans Creutzfeldt and Alfons Jakob. Since then, painstaking detective work by scientists in the United States, Europe, Australia and Japan has followed the zigzag course of the disease.

TSEs, or prion diseases, are not only infectious, they are also inheritable in a very small number of cases. They have no cure and no treatment and no reliable pre-mortem test, so absolute confirmation cannot be made until a post-mortem examination of thin slices of the brain under a microscope reveals massive damage in the form of spongy holes.

The most common form of the disease – sporadic CJD – occurs at a rate of about one in each million people in each country annually, mainly in elderly people. It has no known cause. And those who have died of sporadic CJD (and who have incubated it in the decades before physical symptoms became apparent) have unwittingly transmitted the disease accidentally to others through routes including “donated” pituitary glands, brain lining called dura mater, corneal transplants and contaminated surgical instruments.

Whatever the cause – a yet-to-be identified virus, virino, or “prion” (a corrupted naturally occurring protein) – TSEs are among the worst diseases yet identified. The infective agent appears to bind to alcohol-based disinfectants and resists heating to phenomenal temperatures, freezing, burial underground for years, the strongest of chemicals and conventional surgical sterilisation.

Ignorance of these unusual properties has led to inadvertent outbreaks of iatrogenic (doctor-induced, accidentally transmitted) CJD through fledgling experiments on humans from the 1950s with infertility drugs, human growth hormone (hGH) injections in children, grafts of dura mater in brain and spinal operations, corneal transplantation and the re-use of surgical instruments after procedures on people with CJD.

Well over 3,000 former cannibals from the Fore area of PNG’s mountainous Eastern Highlands succumbed to kuru after repeated feasts in which they ate dead relatives as a mourning rite. The women and children in particular ate the brains and smeared them on their bodies as a mark of respect. There is speculation that this practice may have led to kuru infection via either oral or intraocular routes when, for instance, mothers wiped tiny children’s eyes with their hands. To the end of 2004 more than 170 people who received hGH before 1985, when production of a synthetic version began, have died of CJD in countries including France, Britain, the United States, Australia, Brazil, The Netherlands and New Zealand.

Since 1996 a new branch of the epidemic has shown itself in predominantly teenagers and young people who ate hamburgers, sausages, meat pies and other processed British beef products containing brain and central nervous system tissue (rather than the meat itself) that contaminated by bovine spongiform encephalopathy (BSE) or “mad cow” disease. What constitutes a fatal dose – be it one massive load of infectivity in a single meal or repeated exposure over years, is not known yet.

Now known as variant CJD (vCJD), the human form of BSE had by late 2004 claimed more than 160 lives in Britain mainly – but also France and one each in Italy, Ireland, Hong Kong, Canada and the United States. This is a figure that some experts believe, given decreasing deaths since the new millennium, may indicate that this part of the epidemic is waning. However, others in the TSE research field believe these deaths to be just the short incubation cases, and a potential second phase of the human legacy of the BSE epidemic is yet to show itself. They believe that genetics plays a significant role in whether victims have short or long incubation periods.

In Australia – where all types of CJD became notifiable diseases in 2004 – more than 1500 women were treated with the injectable fertility drug, human pituitary gonadotrophin (hPG) between the 1960s and 1985. It created miracle children, infamous multiple births – and tragedy.

This Federal Government-sponsored hormone extract, made from pituitary glands sliced from the brains of bodies in morgues, has killed four women, all in Australia where the most use of this drug was made, in the years 1988, 1989, 1990 and 1991. One young man, among the 700-odd children who received hGH (human growth hormone) injections between 1967 and 1985 in Australia, has died.

Despite intensive effort fuelled by a damning independent inquiry into the medical program that oversaw the use of these drugs, not every recipient has been traced and warned not to donate tissues or blood.

Lawsuits initiated by devastated relatives angered that no-one took responsibility for human hormone-induced CJD resulted in confidential settlements by the Commonwealth, without admission of liability, in 1994. Most legal claims of psychiatric damage for those “worried well” living with the fear of one day demonstrating clinical symptoms of this disease, that has a latency period of more than 40 years, were settled with one-off payments following a Senate Inquiry in 1997.

In Britain, some of the “worried well” have, in the first cases of their type, been compensated for the psychiatric injury they developed when told that as a result of their human growth hormone treatment they may one day die from a devastating fatal brain disease. In the Queens Bench Division of the High Court up to 40 former hGH recipients in Britain had, up to 2004, pursued psychiatric claims with a range of payments awarded of between £3,500 and £300,000. As well, provision has been made by the court to accommodate claims for the foreseeable future.

CJD and its related diseases incubate in humans for decades. Kuru cases are still emerging, despite the cessation of cannibalism in the late 1950s. The most recent case had an incubation period of well over 40 years.

Infection from blood transfusion has moved from the theoretical to the real – but only in relation to vCJD. In 2004 the world’s first case of probable vCJD was identified in a recipient of blood in Britain six years after a transfusion from a symptomless donor. The donor died of vCJD three years after the donation. A second possible case was reported in 2004 in an elderly woman, also a blood donation recipient, who died of unrelated causes but whose spleen was tested (because she received blood from a known vCJD donor) was found to be full of corrupted prion protein. A third case was reported in early 2006 of transfusion-related CJD.

The legacy of accidental CJD transmission will continue for years to come.

Jennifer Cooke is the author of Cannibals, Cows & the CJD Catastrophe (Random House Australia) which won the 1999 Eureka Science Book Prize, Australia’s most prestigious award for popular science writing.