The UK鈥檚 epidemic of variant Creutzfeldt-Jakob Disease is still growing, according to a new analysis released by the UK National CJD Surveillance Unit in Edinburgh
Doctors are seeing 21 per cent more new cases of the human form of mad cow disease each year, and deaths are rising by 23 per cent. The figures mean that every three months, eight more people go down with the illness and seven die.
However, the predicted trend appears at sharply odds with data from the last few months, which show a marked decline in the numbers of cases and deaths. Up to 1 July, there had been 11 deaths, half the total for 2001 and two fifths of the 28 cases in 2000. The total number of cases is now 124, with 115 deaths.
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But relatively rare diseases are notoriously difficult to track, because small, statistically insignificant clusters or gaps can appear to indicate a changing trend.
Ultimate prediction
However, as time passes, these peaks and troughs usually blend into the overall trend calculated by statisticians. A change in the course of the outbreak can only be stated with confidence if the trend is sustained for a significant period. 鈥淭he significance of the graph is governed by what happens next,鈥� explains Richard Knight, deputy director of the unit. And, he warns, the latest and often incomplete data is always the least robust.
鈥淧redicting the ultimate number of cases is extremely difficult, if not impossible,鈥� says Knight. 鈥淏ut the best fit statistically is still an exponential type of shape.鈥� Independent estimates made since 2000 of the eventual toll from vCJD have varied wildly, from 200 to 136,000.
Cheap meat
Of all possible causes, of vCJD transmission, the report says, suspicion falls most heavily on cheaply produced meat used in burgers and sausages eaten between the mid-1980s and mid-1990s. In late 1995, the UK government banned this 鈥渕echanically removed meat鈥� (MRM) from food on the grounds that it could contain fragments of highly infectious spinal cord.
Figures in the unit鈥檚 report provides some evidence that on average, people with vCJD ate more cheap burgers and sausages that might have contained MRM than healthy 鈥渃ontrols鈥� in the general population.
But this conclusion relies on historical accounts from bereaved relatives of what their loved one ate for the decade before they died. 鈥淒ietary transmission is not proven, but it鈥檚 still the strongest hypothesis,鈥� says Knight.
The report also echoes earlier findings that all the victims so far have the same variant of the gene that produces prions. These are the proteins that become misshapen and clog up the brains of sufferers. 鈥淎bout one third of the population has the same variant,鈥� says Knight.
If the other two gene variants have longer vCJD incubation times, there may be further waves of the disease in the future.
