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TEHRAN, December 11 -Discovery suggests worrying transmission possibilities.
TEHRAN, Young Journalists Club (YJC)-It was probably only a matter of time until someone connected the dots.
Prions – infectious proteins -- had turned up in the eyes of victims of prion diseases.
Infected donor corneas had transmitted prion disease to recipients on at least a few occasions.
And often, patients who later turn out to be infected with prions have eye trouble for which they seek medical attention and testing before they are aware they are infected.
What if … ?
The possibility was horrifying. But it demanded investigation.
Prions are proteins, and, as every biology student knows, proteins are dependent on DNA and RNA for their existence. Yet prions have stumbled upon a way to be self-replicating nonetheless. Their diseased shape induces proteins of similar sequence but healthy shape – found abundantly in all nervous tissue -- to misfold when they collide with a prion. Now they are infectious too, part of a relentless and lethal domino effect.
The diseases they cause are grim. Mad Cow Disease is the most famous, but kuru also possesses a certain notoriety thanks to its unorthodox mode of transmission. Although uncommon, prion diseases are incurable and bring dementia swiftly followed by death.
In the case of spontaneous Creutzfeldt-Jakob Disease (sCJD), the most common prion disease, half of patients are dead within six months of symptom onset. That figure reaches 95% within a year. In a particularly vexing twist, prions are also nearly impervious to destruction, even when attacked using a strenuous combination of disinfectants, heat, and pressure.
As you can imagine, this makes prions difficult to eliminate from infected tissues and equipment.
In addition to corneal transplants, sCJD has also been transmitted by transplants of brain tissue called dura mater, growth hormone from cadavers, and perhaps most worryingly, neurosurgical instruments. So any method that might throw prions into the path of uninfected people deserves scrutiny.
Enter the study published in November in the journal mBio by a team of American scientists that found the eyes of human prion victims are loaded with infectious particles even before they have begun to exhibit symptoms.
Further, these particles are present on the surface of their corneas, the covering of the eye. 100% of the eyes of 11 sCJD victims who donated their bodies for study were seeded throughout with prions. 100% of their corneas contained prion seeding of a “low to moderate” degree.
Because the cornea is enervated, the prions, which prey on proteins found in neurons, may be reaching the surface via these tiny neural conduits.
The retina – the light sensing layer at the back of the eye -- was most densely packed with prions in the inner and outer plexiform layers. They were easily visible in tissue stains.
Source: scientificamerican
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