GUEST ESSAY: Prion diseases: what are they? | Columnists

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RICHARD LEACH, MD

You’ve heard a lot about emerging viral diseases like Ebola, COVID-19 and most recently monkeypox. I bet you’ve also heard of emerging bacteria that are so resistant to antibiotics, such as MRSA and multidrug-resistant Gram-negatives. Have you heard of emerging prion diseases?

A deer hunter friend stopped me the other day. He had read my essay, “Emerging Infectious Diseases and Climate Change.” He wanted to know more about the thing in white-tailed deer called chronic wasting disease (CWD), fearing it was a threat to him. He even wondered if he should give up the hunt. I told him it was good that he knew enough to ask, but he really didn’t need to worry. At least not here in New York State. Not yet. Nor should he worry about prion diseases in general. But yes, chronic wasting disease is slowly emerging, but maybe not because of climate change.

Then he asked another question: what are prions anyway? I told him it was complicated and that I had to write an essay. It’s here.

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First a story

In medical school in 1970, I accepted an autopsy job. It wasn’t that it was a nice job or that I had a morbid side or that it made a lot of money. I actually did it to learn more about the body and how illnesses impact it. This story is about one of my autopsies.

A 50-year-old woman, previously in perfect health, died of progressive and relentless brain deterioration over a period of one year. No neurologist had been able to diagnose it. She came to the autopsy. The brain looked surprisingly normal until I looked at the microscopic sections. Then I saw that the tissue was full of little holes and many brain cells had just disappeared. This set the diagnosis: it was Creutzfeld-Jakob (CJ) disease, a rare entity that kills by creating “spongiform encephalopathy”.

Not much was known about the entity at the time. It was rare and hadn’t prompted much investigation. But about 15 years later, it swept the news and into research labs when “mad cow disease”, more formally called bovine spongiform encephalopathy (BSE), was found to kill some cows in Britain, and was also suspected of killing several as well. people. Horrifyingly, research has indeed shown that the agent can be transferred from infected cows to those that ate the wrong steaks. And the disease that people died with was identical to CJ.

But I’m ahead of myself. In the 1960s, a doctor named Danial Gajdusek was researching another human spongiform encephalopathy called kuru. Kuru was known to be passed from someone who died of it to someone who ate that person. Yes, it was a cannibal disease. It was prevalent in the South Fore tribe in New Guinea. They practiced the ritual consumption of their deceased relatives as a means of preserving tribal memory. Grandma’s brain was considered the best part. Ironic, right?

Anyway, Gadjusek took Grandma’s infected brain tissue, ground it up, and injected it into a chimpanzee. After a long incubation period, the chimpanzee developed kuru and died. This chimpanzee’s brain tissue was then injected into another chimpanzee and – same thing. Gajdusek therefore proved that kuru was caused by an infectious agent. Moreover, he showed that the agent was so small that it could pass through the finest filters, filters capable of trapping infectious agents like bacteria or fungi or parasites. The agent was therefore initially thought to be a small virus. It has been called a “slow virus” because the disease it caused took a long time to develop. Further research has shown that the agent is not a virus at all. It’s a prion, an abnormal protein. More information on this shortly.

Here’s the thing about the autopsy: doing it, I slipped and cut myself with a scalpel. Which meant that my cut was contaminated with the lady’s blood. By studying what was known about CJ at the time and reading Gajdusek’s work on the disease closely related to kuru, I realized that I could have injected myself with a slow viral agent. Which meant my brain….

I was dying of worry every time I forgot someone’s name, telling myself it was coming. Well, I didn’t understand. I’ve never been good with names anyway…which makes it worse…and I can’t remember other things either. Hmm. Probably just age.

What are prions?

They are abnormal proteins. Proteins are large molecules made up of amino acids in a kind of chain. This chain naturally folds back and forth on itself in a very specific way due to mini electrical forces between amino acid atoms. The folding pattern is vital to what they do, and proteins are both the fundamental structural elements of cells and essential players in cellular function.

Consider a glove for the right hand. Turn it over, it becomes a left-handed glove. Like a glove, a protein can sometimes be turned around. It probably happens spontaneously from time to time in a cell. When it does, the protein won’t work, but that’s usually no big deal. Turning a certain type of protein, called PrP, upside down however, won’t work, but, for some reason not yet understood, it will develop the ability to replicate. That’s what a prion is, a misfolded PrP that has self-replicated.

Prion diseases

A lot of PrP exists in the mammalian brain. When a PrP turns around to become a prion and begins to self-replicate, clumps of the substance slowly build up in the pockets. This puts pressure on the neurons, the brain cells, to the point that they disappear. The brain tissue then looks like a sponge under the microscope, with far too few neurons. Of course, the victim descends into progressive brain dysfunction and eventually brain death.

Several spongiform encephalopathies are known. Most occur in non-human mammals: BSE in cattle, scrapie in sheep and goats, feline spongiform encephalopathy in cats, and CWD in members of the deer family. A few occur in humans: CJ disease, kuru, Gerstmann-Straussler-Scheinker syndrome, and fatal familial insomnia. All of these spongiform encephalopathies create the clinical picture of cerebral deterioration in any animal. There is no cure for any of them.

Illnesses can occur out of the blue, called sporadic cases. Sometimes they are passed down in families. Most of the time, prion diseases cannot spread from one species to another. But once in a while, like with mad cow disease, you can.

What about MDC?

Also called zombie deer disease, CWD was first described in 1965 in Colorado. Now present in 29 states, it appears to be spreading slowly, likely through the exchange of bodily fluids between deer. In 2005, only one deer died with him in the southern part of New York. The New York State Department of Environmental Conservation is doing extensive testing on our deer population looking for it. No other cases have yet been reported. But in 2021, a case was discovered 5 miles from our border in Pennsylvania. That’s what prompted my friend’s question.

Unlike mad cow disease, CWD does not infect humans. However, monkeys fed infected deer meat can become infected. The Center for Disease Control and Prevention is therefore not entirely reassuring. They say, “there is no strong evidence for the occurrence of CWD in humans, and it is unknown whether people can be infected with CWD prions.”

So to my hunter friend, I say: be careful, we may soon see the CWD in New York. And for heaven’s sake (and for me’s sake if you decide to give me meat), don’t shoot a staggering, confused looking deer!

One last word

Our bodies are so well equipped to protect us from the wide variety of diseases that exist, it’s just amazing. If we live wisely and well, we can expect a good long life. Then we can enjoy the beauty of supermoons, like the one last week (which was called the “male moon!), be completely stunned by the dazzling images of the universe taken by the Webb Telescope, and gaze in awe our grandchildren grow up. Yes, there are the unexpected love at first sight, like the case of CJ’s disease which may have spared me. But they are rare. We shouldn’t live in fear of them. What we should do is treat our bodies with kindness, like the great gifts they are. The same goes for our environment.

No, my hunter friend, don’t worry about chronic wasting disease. Focus on living wisely and well. Focus on loving neighbors. Focus on leaving the world a better place than when you entered it.

Richard Leach, MD, is a retired internist, infectious disease consultant, and travel and tropical medicine specialist. He practiced in Glens Falls for 35 years, serving as an infection control officer and hospital epidemiologist at Glens Falls Hospital.

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