Chronic wasting disease (CWD) is a prion disease spreading among elk and mule deer in North America. It is similar to mad cow disease, raising fears people eating contaminated venison could develop a form of Creutzfeldt-Jakob disease (CJD) like that blamed on contaminated beef, which has killed about 200 people in Britain.
This is why the latest cases of CJD in hunters, to be reported at the American Academy of Neurology's meeting in Honolulu this week, are causing concern. Two of the men, one aged 64 from Washington state and the other aged 54 from Alaska, were treated by neurologists Natalia Murinova and Ali Samii at the Seattle VA hospital. "These two cases may well have no relationship to CWD in elk and deer," says Samii. "But the fact that it happened in these two patients brings up that question."
The third man died in a different hospital but was from the same town as the hunter from Washington. The two were friends and hunted together.
However, the Centers for Disease Control and Prevention (CDC) will not be investigating the cases because there is no evidence that the men ate CWD-infected meat, says spokesman Ermias Belay. So far the CDC has only investigated CJD cases from states where deer are known to have the disease. But Washington and Alaska are not necessarily disease-free: states do not have to test for CWD until the disease is known to be present.
The CDC has investigated a few suspect CJD cases in the past, and found no compelling evidence of CWD transmission to humans. However, "the data seeking such evidence are very limited", Belay admits.
And that's because not many doctors are looking. For example, Pierluigi Gambetti of the National Prion Disease Pathology Surveillance Center in Cleveland, Ohio, has found that between 1997 and 2002 about 60 per cent of the 921 suspect cases were confirmed as being a prion disease. But these cases amount to fewer than a third of the number that would be expected for the same period based on the rates of sporadic and familial CJD elsewhere, he will tell the Honolulu meeting this week.
That shows how ineffective the surveillance is, says Norman Foster, a neurologist at the University of Michigan in Ann Arbor. So if CWD-contaminated venison does trigger a new form of CJD in people, there could be dozens of extra cases of CJD without them being detected.
Part of the problem is that CJD resembles common diseases such as dementia in the elderly. Doctors have no set guidelines on what to look for and only autopsies can confirm a diagnosis. But few are carried out and CJD is not a reportable disease in the US.
Autopsies can also distinguish between sporadic CJD and the variant form triggered by mad cow disease. But since no one knows what the brains of people with "CWD-CJD" would look like- if the disease does indeed exist- it is hard for pathologists to be sure that a particular CJD case is not related to CWD.
To compound matters further, different federal agencies are responsible for surveillance in humans and animals. Foster and others are pushing for a surveillance programme similar to Britain's mad cow disease and CJD surveillance programmes.
Written by Anil Ananthaswamy
New Scientist issue: 5 April 2003
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