John McCoy: Research raises questions about chronic wasting disease

JOHN McCOY | Gazette-Mail file photo

Sometimes conventional wisdom isn’t as wise as we think.

For decades now, public health officials have told us that there’s no evidence that chronic wasting disease of deer could be transmitted to humans. An ongoing Canadian study has cast doubt upon that.

Since 2009, researchers with the Canadian Food Inspection Agency have been monitoring the health of 21 macaque monkeys exposed to CWD. Macaques were used because they are genetically the most human-like animals upon which scientific research can be performed.

Some of the macaques were exposed via injection, and some were exposed by being fed infected venison from white-tailed deer. Ten of the macaques have since been examined for CWD.

Two that were exposed to the disease by injection were found to be infected. One that was fed infected brain tissue also became infected. Most disturbing, two macaques that were fed venison containing CWD proteins showed evidence of infection.

“The assumption was for the longest time that chronic wasting disease was not a threat to human health. But with the new data, it seems we need to revisit this view to some degree,” said Stefanie Czub, the lead researcher, in an interview with a magazine in British Columbia called The Tyee.

Macaques aren’t human, so there’s still no ironclad evidence that people can contract CWD by eating venison from infected animals. Clearly some primates can.

Health Canada, that nation’s government health service, isn’t taking any chances. After the preliminary results of the macaque study were made public, agency officials issued the following advisory:

“While extensive disease surveillance in Canada and elsewhere has not provided any direct evidence that CWD has infected humans, the potential for CWD to be transmitted to humans cannot be excluded. In exercising precaution, [Health Canada] continues to advocate that the most prudent approach is to consider that CWD has the potential to infect humans.”

In Wisconsin, where CWD has become a significant problem, the state Department of Health Services has recommended that hunters not eat or share venison from deer killed within the state’s CWD Management Zone until those deer are tested and determined to be disease-free.

Scientists classify CWD as a “transmissible spongiform encephalopathy,” or TSE. That means the diseases, once contracted, create sponge-like voids in the brains and nerves of the animals they infect. “Mad cow” disease is a TSE. So is scrapie, which is found in sheep.

Five TSE-like diseases have been discovered in humans; of those, Creutzfeldt-Jakob disease is the best known. Nationally, the number of people who contract Creutzfeldt-Jakob has risen since CWD became prevalent. Scientists don’t believe there’s a correlation, but they urge caution.

Since 2006, when CWD first showed up in West Virginia’s Hampshire County, Division of Natural Resources officials have urged hunters to take minimize contact with brains, spinal cords, eyes, spleens and lymph nodes of deer killed in the state’s CWD Containment Area. No warnings have yet been issued about eating the venison.

Future research on macaques might change that. Time will tell.

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