About the SA Blog Network



Opinion, arguments & analyses from the editors of Scientific American
Observations HomeAboutContact

Natural Born Prion Killers: Lichens Degrade “Mad Cow” Related Brain Pathogen

Email   PrintPrint

lichen-degrade-prions-mad-cow-chronic-wasting-diseaseRemember mad cow disease? In the 1980s, cattle in the U.K. had begun contracting a fatal brain ailment triggered by an infectious protein called a prion. The pathogen could spread to humans who ate contaminated beef. Officials brought the bovine epidemic under control with major changes in agricultural practices.

Unfortunately, the same cannot be said for a cousin of the sickness, one that targets deer, elk and moose in the U.S. Called chronic wasting disease (CWD), or "mad deer" disease, the ailment poses an unusual challenge in that it has spread among wild populations, not among herded animals. Wild animals go where they may, so you cannot institute controls the way you can for livestock. So it comes as good news that a naturally occurring disinfectant exists within common lichens and might actually be able to stop prions in the wild.

What has made prions difficult to control is their infamous durability. Boil water for a few minutes, and all the bacteria and viruses will be gone. Not so for the prion: it will be just fine, ready to infect. How does it fare in a dry heat of 600 degrees C? No problem there, either. How about ionizing radiation? Bring it on.

The prion’s stubbornness caused many unfortunate medical mishaps in the days before researchers knew what they were dealing with. In the 1970s, electrodes used to treat epilepsy spread a human prion disease from one patient to another even though the electrodes had undergone standard sterilization and sat for 18 months before reuse. In a later test on monkeys, electrodes maintained their infectivity even after three bouts of sterilization. In the late 1980s, the processing of cadaver tissue—specifically, a brain lining called the dura mater that is sometimes used as a patch in neurosurgery—failed to inactivate prions from infected donors, leading to the transmission of a fatal brain disease to healthy recipients. (I recount these and other incidents in my 2003 book on prions.)

And the prion’s resistance to inactivation is a big reason why mad cow disease spread: to save money, the makers of cattle feed, which spread the illness, had eliminated the use of solvents and extended heating that probably would have disabled the prion. In decontaminating an area that once harbored infected farm animals (such as sheep), U.S. officials spray down hard surfaces with a caustic solution such as sodium hydroxide (better known as plumber’s lye), turn over several centimeters of soil to bury any prions on the surface and deem the land off-limits for years. Such draconian measures are one reason why farmers dread the diagnosis, even with government reimbursement for the loss.

Of course, such techniques won’t work in wild animals, which spread prions via their urine, feces and saliva. First identified in the late 1960s, chronic wasting disease has been detected in deer, elk and moose in 19 U.S. states and two Canadian provinces (although much of that spread resulted from the transfer of animals for game ranches). Although no human has contracted CWD from eating venison or other cervid meat, the lessons from the mad cow epidemic led game officials to conduct massive culls and establish stricter butchering guidelines to prevent contamination from brain and spinal tissue, where infectious prions collect.

So news that a natural answer exists for prions is welcome. In a paper published May 17 in PLoS One , Christopher Johnson of the U.S. Geological Survey of the National Wildlife Health Center in Madison, Wisc., and his team describe experiments with lichens, symbiotic collections of algae, fungus and bacteria that casual observers might mistake for moss. Three common species of lichens, the team has found, exude an enzyme that breaks down the prion.

The scientists achieved the results in a test tube, but they suspect that lichen power will work in the wild. "While great caution must be exercised in extrapolating in vitro studies to environmental conditions, our data suggest lichens could contribute to prion degradation on the landscape," they wrote, noting that inactivation might occur when prions come into direct contact with the lichens or with nearby soil. The team plans to test the hypothesis and even see if animals are protected from CWD if they eat the lichens.

Image of lichen Parmelia sulcata courtesy of Derrick Ditchburn/U.S. Geological Survey


Rights & Permissions

Comments 8 Comments

Add Comment
  1. 1. ConcernedCitizen 4:25 pm 05/19/2011

    Since prions are a misfolded version of the normal human PrP(c) protein, seems like the lichen would, at best, be toxic to animals. Although if you have a book on prions, you probably already know this and are mainly writing this article to plug your book…

    Link to this
  2. 2. pyam 6:03 pm 05/19/2011

    Oh please. If I wanted to mainly plug my 8-year-old book, I’d be writing about prions all the time. I mentioned it because I don’t have links to individual medical cases as an easy reference.

    To answer your question about toxicity, the enzyme may not be toxic because the body may be able to break it down–and it may not even be able to enter the brain. The researchers are speculating that a deer that happens to consume both prions and the lichen around the same time could experience protection from infection. This of course is all speculatin that needs to be tested.

    Link to this
  3. 3. amanzed 7:17 pm 05/19/2011

    I appreciated Philip Yam’s article and learned something from it. As a science-trained writer, I admired the style and choice of subject matter.

    ConcernedCitizen’s peevish comment reflects a disturbing towards knee-jerk cynicism and fixed thought patterns — a shame.

    Who better to (occasionally) write on a subject than an author of a book on the subject?

    If you want to play ConcernedCitizen’s cynical game, it’s really easy and requires no actual thought or expertise. Here’s the flip side of his or her "point", written for the case where the author didn’t have a book under his belt:

    "Although if you [haven't written a professional book or scholarly article] on prions, you probably [don't know even this basic fact] and are mainly writing this article [for the per-word fee and public exposure]…"

    Link to this
  4. 4. amanzed 7:19 pm 05/19/2011

    … disturbing [trend] towards…

    Link to this
  5. 5. bgroeper 7:23 pm 05/19/2011

    I find this great news. I was in the UK in the 80s and consumed beef. Every so often I have a moment of worry (ok periodic freak out when I read about Mad Cow) that I am going to get the human version. The Red Cross doesn’t want my blood donation last time I offered because of the time I spent there. This breakthrough just make me love nature and its balance sheet more and more. I hope it continues to be promising.

    Link to this
  6. 6. hlasny 2:52 am 05/20/2011

    However, mad cow disease (BSE) can be a naturally occurring disease, and not an infectious disease, so beef is safe in the all world. WHY?
    The BSE was tested in dairy cows, see"nutritonal experiment" performed in England; published in Veterinary Record (MOORBY et al., 2000) and in Journal of Dairy Science (MOORBY et al., 2000; DEWHURST et al., 2000). Long-term dietary crude protein surpluss, significantly higher than the norm (NRC, 2001; if about daily 30 kg of milk production was recorded and six of the 47 animals (13 percent !!!) developed clinical signs of BSE…
    In addition about the BSE/ vCJD diseases; this was never justified scientifically! It was pure, math-model-driven science fiction. See more about ; BSE/ vCJD mathematical- models, see my large three comments in
    ( But it was pushed very vigorously by the British science establishment, which has never confessed to its errors… WHY? Because, in 1996, a variant form of CJD (vCJD) was discovered in small clusters in Britain. It was immediately suspected that the outbreak of BSE could be connected to the clusters of vCJD in humans. People were cautioned not to eat beef that may come from diseased cattle, for fear the disease could be transmitted to humans via the meat products they consumed…

    In Canada in recent years, isolated cases of BSE still are found. Recently, last case was detected in a cow aged six years, so still in age of higher milk production. My recommendation? Examine in detail the level of nutrition of this cow in the last year and the result of a study to compare with the British experiment. I have no doubt that will be conclusion, that BSE positive cow received a high concentration of protein with lower utilization of magnesium, in the feed ration So even in Canada is not an infectious BSE disease and the effect of meat and bone meal can be excluded…

    Similarly, particularly in the U.S. was encouraged to a high concentration of protein in deer feed rations. See my comment (March 12, 2009) at this address;–3315-0312 From this comment should be cite at least the following; There are also recommendations; about the high protein intake in deer and elk rations, see these U.S. literature sources; Elk that are rapidly growing or lactating and bulls recovering from the rut have higher protein needs. To some extent, greater protein requirements can be met by increased intake. However, the percentage of protein in diets designed for these animals is usually increased as well. Maintenance rations should be at 10 – 12% crude protein, whereas rations for lactation or antler growth should provide 14 – 18% crude protein. Growing rations should contain 16 – 20% crude protein….
    According to my opinion; what is the common denominator of the neurodegenerative diseases, including Alzheimer’s disease?This was ten years ago (end of March 2001), when I published an alternative theory ( BSE ammonia- magnesium theory), where the main role of NMDA receptors was described. According to this theory, the cause of BSE is an excess of protein and the magnesium deficiency, in the feed rations of ruminants. Such conditions were developed in the mid of 1980s , especially in Great Britain.
    The neurodegenerative diseases, occurred to a greater extent, only in ruminants (BSE), because only in them, magnesium is not absorbed in the intestine, but in the rumen. The excess of protein-nitrogen in the rumen decreases absorption of magnesium. Most suffer with magnesium deficiency, high yielding dairy cows, in which high milk production leads to the dysbalancy between calcium and magnesium. Prolonged magnesium deficiency leads to an excess of calcium in animal tissues, and NMDA receptor hyperfunction. From the period around 1985, new dietary standards are known in dairy cows (eg, NRC 1985…), which began recommending high concentration of protein in the feed rations of cows.

    In addition, on this website (December 2010) , there was described the effect of drugs, in Alzheimer’s disease in humans, on the principle of control hyperfunction of NMDA receptors, which is consistent with my BSE alternative theory of BSE, published 10 years ago. See more about the Nameda; A medication known as Namenda® (memantine), an N-methyl D-aspartate (NMDA) antagonist, is prescribed to treat moderate to severe Alzheimer’s disease. This drug’s main effect is to delay progression of some of the symptoms of moderate to severe Alzheimer’s….
    And what is about the plasminogen and the NMDA receptors relationships? Scientists have discovered that a protein plasminogen, speeds up the progress of prion diseases such as mad cow disease. They found that the natural replication of the prions (from PrP to PrPSc) was stimulated by plasminogen in both human and animal cells. To clarify the role of plasminogen as a cofactor for prion propagation, they conducted functional assays using a cell-free prion protein (PrP) conversion assay termed protein misfolding cyclic amplification (PMCA) and prion-infected cell lines. They report that plasminogen stimulates propagation of the protease-resistant scrapie PrP (PrPSc). Compared to control PMCA conducted without plasminogen, addition of plasminogen in PMCA using wild-type brain material significantly increased PrP conversion. Their results demonstrate that plasminogen functions in stimulating conversion processes and represents the first cellular protein cofactor that enhances the hypothetical mechanism of prion propagation.
    However, the serine protease, tissue-type plasminogen activator (tPA), is known for its ability to cleave the pro-enzyme plasminogen into the potent protease plasmin. The”tPA” is recognized as a modulator of glutamatergic neurotransmission. This attribute is exemplified by its ability to potentiate calcium signaling following activation of the glutamate-binding NMDA receptor (NMDAR). As a result, several recent studies which show interplay between tPA and the NMDAR have received considerable attention A persuasive body of evidence suggests that tPA can directly (i.e. in a plasmin-independent manner) cleave the NR1 subunit and thereby increase the Ca2+-permeability of the NMDAR.
    However, less well-known circumstances can be show (as a detective story); in documenting the first case of disease transmission, by blood transfusion. For more informations see my large comments in The Western Star ( ).
    See also other relationships (why great progress about BSE eradicating within the… EU?), according to my web and recent presentation at 29th World Veterinary Congress in Vancouver;Neurodegenerative Diseases and Schizophrenia as a Hyper or Hypofunction of the NMDA Receptors (

    Link to this
  7. 7. iarlakd 9:03 am 05/20/2011

    If proven, this will have a big impact on reducing medical costs as it will provide a chemical mechanism for the sterilisation of medical instruments. Prions have caused vast rafts of surgical devices to become single use as it’s no longer feasible to sterilise them.

    Link to this
  8. 8. Brielll 2:47 pm 05/21/2011


    Its about time somebody spoke up for Lichens.

    Lichens have always been considered throw away species in PNW forest plan EIS’s. But below is an analysis of how big the forest reserve would have to be to protect Lichens at the viability we protect salmon or spotted owls. Basically you have to stop cutting the existing forests, then buy up the remaining private forests and add them to the national forest system and put the new forest in reserves too.

    For a viability analysis of how large a forest reserve you need to protect the Lichens see:

    Another more formal published version of the above viability analysis is here:

    Lichens also absorb radioactive isotopes from the air which is why reindeer died after Chernoybl…from eating Lichens.

    In order to keep forests healthy all the stuff that runs off during rain must be replaced and put back where it came from and Lichens are important in this process, and apparently each species of lichens contributes different and very obscure and ineffable things to forest health.

    From the devils environmental dictionary,

    DYSERGY, ant. to synergy. unpredictable, disagreeable outcomes created by tinkering with or simplifying complex systems. e.g. disease, floods, fire or famine, [four horsemen].


    Jim Britell

    Link to this

Add a Comment
You must sign in or register as a member to submit a comment.

More from Scientific American

Scientific American MIND iPad

Give a Gift & Get a Gift - Free!

Give a 1 year subscription as low as $14.99

Subscribe Now >>


Email this Article