Swiss CJD rise raises alarm

BSE-related brain disease could emerge in different form.
12 July 2002

HELEN PEARSON

Cows are thought to have caused a rise in variant, not sporadic CJD. © alamy

The number of people dying from sporadic Creutzfeldt-Jakob disease (CJD) has risen sharply in Switzerland. The finding is raising fears that 'mad cow disease' could have spread to humans in another form¹.

In Britain, a cattle epidemic of BSE is thought to have triggered a brain disease called variant CJD in some people who ate infected meat products. Variant CJD strikes young people.

Four years after Britain's BSE outbreak, Swiss cattle were also hit by a BSE epidemic, which peaked in 1996. Now Swiss epidemiologists have recorded an alarming rise in apparent cases of sporadic CJD, a different form of the disease that affects those over 60.

Each year between 1997 and 2000, 8 to 11 of Switzerland's 6.5 million people developed CJD. In 2001, 19 cases were reported; 7 were reported in the first quarter of 2002. This is around four times higher than the reported incidence anywhere else, including Britain.

There are many possible reasons for the climb - including a simple statistical variation or improved disease reporting. The most alarming possibility is that BSE has passed into humans and caused sporadic CJD. At present, it is impossible for scientists to judge if this has occurred.

Blip or climb?

The hike may be a random statistical blip - in which case next year's figures may fall. Fluctuations have occurred in the UK sporadic CJD figures over the past few years. "I'm still hoping the numbers will go down," says the researcher who led the study, Adriano Aguzzi of the Institute of Neuropathology and National Reference Center for Human Prion Diseases in Zurich.

Epidemiologist Roy Anderson of Imperial College of Science, Technology and Medicine, London, says his "preferred option" is a reporting bias: that an increased awareness of the disease amongst doctors and the public has produced more diagnoses.

But Aguzzi thinks that over-reporting is unlikely. He points out that other countries - Britain, Austria and Germany - who spend as much on CJD surveillance have not reported similar sharp increases.

The infectious prion protein that causes CJD could also have been transmitted from one patient to another via surgical instruments, blood transfusions or some other medical procedure. "It's a distinct possibility," says Aguzzi. Whether this is so would become clear through scrutiny of clinical records.

Worst-case scenario

If BSE is the cause of Swiss sporadic CJD - the worst-case scenario - researchers have to work out how the cattle disease can cause two different forms of the human disease: variant CJD in Britain and elsewhere in Europe, and sporadic CJD in Switzerland.

This could be explained if British and Swiss cattle harboured different strains of the infectious prion protein - but preliminary experiments suggest that they are the same.

Alternatively, Swiss CJD could have leapt to humans through the injection of vaccines or medicines produced using serum made from cows, suggests Cornelia van Duijn of the European collaborative group on CJD incidence at the Erasmus University Medical School in Rotterdam, The Netherlands. Finding the source of the disease has "got to be priority number one for Europe", she says.

Researchers now hope to establish whether sporadic CJD came from BSE. They will use 'strain typing': infecting mice with the prions causing the two diseases and seeing if the symptoms match up. "It's the best way to establish or exclude any suspected link," says Moira Bruce of the Institute for Animal Health Neuropathogenesis Unit in Edinburgh, UK. These experiments will take at least a year.

1. Glatzel, M. et al. Sharply increased Creutzfeld-Jakob disease mortality in Switzerland. Lancet , 360, 139 - 141, (2002).