They’re called TSEs, for Transmissible Spongiform Encephalopathy, contagious diseases in which brains are destroyed by mis-shapen proteins called prions.
For the most part these are diseases that affect animals, but one, BSE, popularly known as “Mad Cow Disease” could be transmitted to humans. 230 people worldwide have been diagnosed with the human version, Variant Creutzfeldt-Jakob disease.
“Mad Cow Disease” affected its victims’ brains and spinal fluids, but did not spread to other parts of the body. This made it less transmissible, and may account for the relatively small number of human and bovine cases.
There is another TSE called Chronic Wasting Disease (CWD), and it has turned up in various species of deer and reindeer, moose and elk. So far, studies by the Centers for Disease Control say, they’ve had no cases of CWD in American humans. Animal studies in genetically altered, “humanized” mice and macaque monkeys, who are biologically very close to human, have also showed no tendency to catch the disease. But tests of spider monkeys, who are less like us, showed they did take up the illness, did develop bent prions, which did proliferate. This is seen by scientists studying CWD as a cause for concern.
But here’s the really worrying news about CWD – Chronic Wasting Disease – unlike “mad cow disease” it is very transmissible among animals to where today, Colorado wildlife monitors believe 57 percent of deer herds and 37 percent of elk herds in the state are infected.
How could this have happened with a disease that was first identified in a single deer in Northern Colorado just over 50 years ago?
Here are three big factors:
- CWD starts slowly and silently. It can incubate in an animal or a herd for years before showing any symptoms.
- The prions that drive the disease can be spread through saliva, blood, urine, feces or flesh from a sick animal, can infect soil and vegetation, which when eaten can further spread the disease.
- Killing sick prions, rendering them harmless is very hard to do. Most attempts at CWD prion eradication, and there have been several serious ones, have failed.
For years, for these reasons, infectious disease experts have been constantly testing for human CWD. But now there’s something new to worry about…Deer, reindeer and Moose in Norway, Sweden and Finland have been found with CWD, and tests suggest, their CWDs may be different from the American version, and maybe even from each other, which may mean CWDs like TSEs come in several different varieties, but it could also mean these differences are evidence of a disease that is still adapting, still mutating in ways that could eventually lead it to humanity.
Rae Ellen Bichell is a reporter with Mountain West News Bureau. She previously covered biomedical research and basic science for National Public Radio.
Bichell learned the audio ropes at member stations in Nashville and Seattle, and at NPR as a 2013 Kroc fellow. As a Fulbright grantee in Finland, she learned that ice swimming and reindeer spine soup are not only tolerable, but even enjoyable.
At Yale, she studied anthropology, journalism, and anything that involved handling insects and plants.