No matter whether one views the outcry over US beef imports as a scientific, political or diplomatic problem, it is a matter of keeping mad cow disease out of Taiwan, which has so far been free of it.
Unlike Europe, the US and Japan, Taiwan has had no cases of bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, or its human equivalent — the transmissible variant of Creutzfeld-Jakob Disease, variant CJD or vCJD for short.
However, objective medical evidence shows that Taiwan is more vulnerable than Europe and the US to the spread of vCJD. For the sake of this and future generations, we should resolve to keep Taiwan free of the illness, even if doing so is more costly for us than for other places.
Genetically, Taiwanese people are a high-risk group for vCJD. When scanning the gene sequences of vCJD patients, European and US scientists found three polymorphic subtypes of the prion protein gene (PRNP) at codon 129 — MM, MV and VV, referring to the pairing of amino acids methionine and valine. All patients infected with vCJD from bovine protein were found to have the MM genotype.
This finding clearly shows that people with the MM genotype are a high-risk group for infection with vCJD from cows with BSE.
In Britain, which has had more vCJD cases than any other country, only 38 percent of the population has this genotype, yet 100 percent of British vCJD patients had the MM-type gene. According to the work of Taiwanese researchers (Wang et al, 2007), as many as 98 percent of Taiwanese people have the MM genotype. It can therefore be said that almost everyone in Taiwan is a member of the high-risk group for vCJD.
UK scientists studying a 1950 outbreak of cannibalism-related human spongiform encephalopathy in Papua New Guinea, where the illness was called Kuru, found that when the disease was spread by the prion from human flesh, it could incubate in the human body for as long as 50 years (Collinge J et al, 2006).
In the Kuru case there was no species barrier to infection, since the disease-causing prion was passed from one member of the human species to another. In the case of beef prions, when they are passed from one species (cows) to another (humans), thereby crossing a species barrier, the incubation period may be even longer.
Research on the history of vCJD in the UK has shown that blood transfusions are one way in which the illness can be passed from one person to another. The scary thing is that blood donors may pass on the disease during the incubation period.
Clinical cases show that the blood of vCJD carriers is infectious for three-and-a-half years before the onset of symptoms. The vCJD prion can lurk within the human body for a long time, and at present there is no way of detecting it.
Potentially, it could be transferred through blood transfusions for up to 50 years, making the spread of the illness very hard to control.
A 2004 study revealed that in a UK survey of 12,700 surgically removed appendixes, three appendixes stained positively for prion protein accumulation. This indicates a higher-than-expected rate of CJD infection, equivalent at a national level to thousands of infected individuals (Hilton DA et al, J Pathol. 2004 Jul;203(3):733-9).
Taiwan is very densely populated and Taiwanese are accustomed to eating beef innards. These factors make it easier for mad cow disease to spread in Taiwan than in Europe and the US.
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