Creutzfeldt-Jakob Disease (CJD) occurs very rarely. There are several types of CJD. Worldwide, the number of new cases of CJD per year (incidence) is about one case per 1 million people. No clearly identifiable cause for this disease is known.
Symptoms and types of Creutzfeldt-Jakob disease
The sporadic type is characterised by rapidly progressive dementia. In the early stages of the disease, mood disorders or disorders in the sense of reality can occur. Other symptoms quickly appear, such as spasms, language disorders (aphasia) and problems with perception. Symptoms that resemble drunkenness occur in more than half of the patients. The severity of the symptoms increases rapidly within a few months. The average survival is four to five months. The same symptoms are also seen in the hereditary type of Creutzfeldt-Jakob Disease (CJD).
A third type is "iatrogenic" CJD. This means that the infection is the result of medical treatment. Examples include use of growth hormone originating from the brains of the deceased, neuro-surgical procedures or transplantation of cornea. The incubation time of this type is between 18 months and 10 years, and in some cases up to 30 years. The symptoms of iatrogenic CJD are slightly different from the sporadic type. The onset of the disease is characterised mainly by coordination disorders, while symptoms of dementia occur much later or sometimes not at all.
Genetically determined sensitivity to prion disease
Research has shown the possibility of genetically determined sensitivity to the development of prion diseases. The code for the prion gene is located on the human chromosome 20. In the human population there are two versions of this prion gene: M and V. Because chromosomes always occur in pairs, three genotypes are possible: M/M, M/V and V/V. The genotype M/M has been found to occur much more frequently in patients with CJD (in 83% of patients) than in the total population (36% M/M). In patients with CJD, genotype M/M has been found in all patients to date. Apparently, these people have a genetic predisposition that makes them more susceptible to the pathogen that causes BSE.
In 1959 a brain disorder was observed in a tribe in the highlands of New Guinea. This condition was called "kuru" and was characterised by gait disturbances, followed by tremors, loss of control over other movements and dementia at a later stage. After three to nine months, the disease was fatal. Only women and children became ill, and the men did not. It turned out that the tribe had a mourning ritual during which the women and children rubbed themselves with brain tissue from deceased tribesmen and sometimes ate the brains. In infection trials with chimpanzees, it was shown that the brain tissue was infectious. Subsequently, the mourning rituals were abolished and the number of affected people gradually decreased. In those born after 1959, kuru was no longer observed.
Gerstmann-Sträussler-Scheinker Syndrome (GSS)
This prion disease is hereditary and occurs in approximately one in 10 million people. The cause is a mutation in the prion gene. This mutation is not the same for all families. Various mutations of the prion gene have been identified. The disease is characterised by problems with making coordinated movements. These problems increase gradually in severity. Patients walk as if they are inebriated and give the impression of being very clumsy. The disease progresses more slowly than Creutzfeldt-Jakob Disease. On average, patients die after five years, but in a number of families the disease duration is 10 to 20 years. Within a family, the disease can take many forms.
Familial Fatal Insomnia (FFI)
This is a hereditary prion disease, which occurs very rarely. The disease occurs in some Italian and American families. It is characterised by insomnia and a disturbed day-night rhythm, which also affects blood pressure, heart rate, body temperature and hormone levels. Hallucinations and panic attacks also occur. In the final stage of the disease, dementia also occurs. FFI patients die after an average disease period of 18 months.
Danger to the consumer?
Presently, the risk of someone contracting BSE by eating Dutch beef products is negligible. All cattle older than 30 months are tested for BSE before their meat becomes available for consumption. Cattle in which a BSE infection is detected by the test are destroyed. Moreover, Specified Risk Materials (SRMs – materials that pose an infection risk) from all other cattle older than 12 months are removed during slaughter and subsequently incinerated. This is to prevent animals that are at a very early stage of the disease, which is possibly not detected by the test, from causing infections.
Between 1997 and 2000, not all animals were tested, but the SRMs were removed to minimise the risks for consumers.
Before 1997, people might have been infected by BSE, but in the Netherlands the use of brain material in the food chain has always been very limited, in contrast to countries such as Great Britain. Thanks to our quick response with BSE controls, few BSE cases occurred in the Netherlands, which means that the infection pressure for humans was limited. This low infection pressure, combined with the very restricted use of SRMs in human food, leads us to expect that no people in the Netherlands, or very few, are currently infected with BSE.