The race is on to find out whether a fatal brain disease in deer and elk poses a risk to human venison eaters. “That’s what everybody is trying to find out,” said Dr. Pierluigi Gambetti, head of a national team studying the occurrence of the deadly protein disease.
Perhaps most significantly, a National Institutes of Health laboratory in Montana is planning to experiment with primates to try to determine human susceptibility to chronic wasting disease.
“Primate research is the most direct way to find out if people are susceptible,” NIH research scientist Richard Race said. “It’s the species that’s most closely related from an evolutionary point of view to people. You cannot inoculate humans on purpose, so the next best thing is some kind of a non-human primate.”
But even with the groundbreaking research, Race said, answers are unlikely to come anytime soon. The process could take years, he said.
Meanwhile, Gambetti’s group and others are gearing up for studies of genetically manipulated mice to see if they can be infected with chronic wasting disease.
“We don’t know whether it can be transmitted to humans and, if it is transmitted, what it’s going to look like,” Gambetti said.
There are no proven cases of chronic wasting disease infecting humans, but concern has intensified as the disease has spread from its endemic areas in Colorado and Wyoming to several other states and two Canadian provinces.
There have been several cases reported in which human venison eaters have contracted Creutzfeldt-Jakob disease (CJD), which, like chronic wasting disease, is a transmissible spongiform encephalopathy (TSE), but one that occurs naturally in humans.
Gambetti said that these cases seem to fit into known subtypes of CJD, but he added that the assumption that human cases from deer or elk would look different upon microscopic examination than ordinary CJD is just that – an assumption.
Most scientists believe all TSEs – CWD, CJD and mad cow disease in cattle – are all caused by a mutant protein called a prion.
Most scientists believe there is a strong barrier preventing prions from one species from infecting another. But 131 European beef eaters have contracted a variant of CJD caused by eating cattle suffering from mad cow disease, or bovine spongiform encephalopathy (BSE).
That has sparked concern that other spongiform encephalopathies, including CWD, could jump to humans or livestock.
Using primates to search for answers is a costly and potentially controversial step, acknowledged Bruce Chesebro, head of the laboratory of persistent viral diseases at the NIH facility that will conduct the research.
Race, the chief scientist involved, knows the pitfalls. “No matter what the outcome, there are going to be people who fault how it was done,” he said. “One of the reservations we have is that there are no right answers. Whatever you give the primates, some people are going to say you gave them too much. Some people will say you didn’t give them enough.”
And there’s a political aspect, as well, Race acknowledged. “If word gets out that it’s actually being done, you get all the animal protest groups and people like that bugging you all the time,” he said. “One thing about it if we do it here (at the lab in Hamilton, Mont.) is that security is really tight.”
Race is the lead researcher on a continuing mice experiment that has shaken the prion field.
In it, hamster prions were injected into mice, which then showed no outward or microscopic sign of the disease. However, when brain matter from those mice is injected into another set of mice and hamsters, they become sick from mutant prions and die.
No one knows how these “sleeper carriers” stay healthy, or why subsequent test animals become sick. But it raises the concern that if CWD infected other animals, it is possible that at least the first generation of the infected species might not get sick.
“It used to be thought the hamster (prion disease) didn’t go into mice. There was a species barrier,” said Anne Raines, a fellow scientist at Rocky Mountain Laboratory. “And now we have some of those mice going down in a short amount of time – 100 days or so.”