Introduction
With the epidemic of bovine spongiform encephalopathy (=BSE) in Great Britain it was noted that some cases of Creutzfeldt-Jakob disease have increased in frequency.
The more common form of the disease is transmitted by contact with infected nervous tissue from BSE infected animals (acquired cases). The underlying cause of Creutzfeldt-Jakob disease seems to stem from the same prion that causes mad-cow disease in cattle when they are fed scrapie-infected sheep brains.
This is why it is also called human mad cow disease. The above FDA link gives you more background about the story of the single cow in the US that was identified. As the BSE prion is very resistant to normal disinfection practices, transmission between species is possible. The less common cases of Creutzfeldt-Jacob disease are due to genetically caused familial Creutzfeldt-Jakob disease. The familial form is transmitted in an autosomal dominant fashion. According to newer information from longterm studies in Great Britain it can take up to 15 years of incubation before a known contaminated person comes down with the disease, although most patients will turn sick faster (Ref.14).
BSE symptoms
In most cases the onset is gradual with memory loss in the mid-life range, which deteriorates over weeks or months. However, in about 15% there is a fulminant course where within days or weeks sudden dizziness is followed by double vision and blurred vision and rapid deterioration of mental functioning. Both forms of the disease display personality changes with irritability and self-neglect.
Reading and writing are deteriorating, recognition is slow and hampered. Patients are easily fatigued and have sleep disturbances. Eventually a repetitive muscle shaking, called “myoclonus”, occurs with relatively minor skin touch. Dysbalance due to cerebellar and major nerve tract involvement leads to gait problems. When the basal ganglia are involved, muscle rigidity and grotesque posturing are often in the foreground. Eye movements are often affected, but visual defects are also common as is central blindness (with involvement of the optic tracts from the eyes to the visual fields of the brain). Only about 8% will last longer than 2 years, the majority succumb to the disease after 3 to 12 months.
Diagnostic tests
Unfortunately there is no reliable noninvasive screening test for early Creutzfeldt-Jakob disease. However, in the established disease case the cerebrospinal fluid, which can be tested with a special protein test, will show with a 96% specificity and sensitivity whether the disease is present (Ref. 5). In the more progressed disease there are changes on CT scans or MRI scans. However, a normal scan does not rule out existing disease. Electroencephalography (=EEG studies) might show sharp waves and spikes that are typical for this disease. The most reliable test would be a brain biopsy, which is an invasive test, but shows typical histological changes for the disease. There is technology that allows rapid BSE testing in humans and animals.
Treatment
Unfortunately at this time there is no known therapy for Creutzfeldt-Jakob disease. Research is being conducted into the possibility of using protease inhibitors for prions. Unfortunately such research often takes many years before clinical trials can be conducted.
The prognosis is therefore still very grim with most patients dying within 1 to 2 years from the point of diagnosis. There have been reports in early 2005 that an old drug, namely pentosan polysulfate can be effectively used to abort the course of human BSE cases. But further studies showed that more research is needed to investigate this experimental treatment.
Prevention
Avoidance of nervous tissue infected with prion disease (such as BSE) is important. This includes salami sausage and other sausage wherever ganglion or nervous system tissue of cattle or sheep is mixed in. Studies have shown that standard cooking methods do not inactivate the prion. It requires steam autoclaving (under pressure) for 1 hour at 132°C, which is difficult to do.
So, how safe is it to eat beef?
According to Dr. Robert Reynolds, an infectious disease specialist at the Vancouver General Hospital of the University of BC/Canada there is a 1:32 million chance of contracting mad cow disease (variant form of Creutzfeldt-Jacob disease or BSE) from eating a steak. This is considered to be an extremely low probability when you consider that the probability of being hit by lightening in North America is 3850-fold higher, being hit as a pedestrian 38,500-fold higher, falling at home 189,000-fold higher and dying in an automobile accident 420,000-fold higher.
References:
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14. The 50th Annual St. Paul’s Hospital Continuing Medical Education Conference for Primary Physicians, Nov. 16 – 19, 2004
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