One of the strangest things that can make us sick – a deceptively misfolded protein that destroys the brain, known as a prion, is even scarier than we knew. Researchers were able to find the prions responsible for the sporadic Creutzfeldt-Jakob disease (sCJD), the most common prion disease in humans, which is affected in the eyes of 11 patients.
The findings are the last to suggest that these universally fatal, or rare, diseases can be spread through the eyes. But they also indicate that one day our eyes can be used to recognize these cases with less effort than the current test methods.
We can get sick of prions in some ways. Sometimes people are born with mutations passed in their family that increase the risk of developing prion disease, including a form of CJD. Usually, just as with people with sCJD, the prions emerge spontaneously, whereby the normally harmless prion protein turns into a misfolded form, which means that proteins in the environment can also be folded incorrectly. But what is especially frightening about prions is that they can also be contagious, capable of spreading from person to person or even from animal to person.
It may take years, even decades, before the symptoms of a prion disease (such as dementia or muscle weakness) start to appear, but once they do that, it is usually only a matter of months before death.
The most notorious example of transfer from person to person is that of Kuru, a disease spread across the Fore tribe of Papua New Guinea through their ritual practice of eating the brains of deceased loved ones. (When the Fore people stopped eating human flesh in the 1960s, kuru was exterminated.) But people can also catch CJD from contaminated surgical instruments that hit the brain or get around, as well as certain types of transplants from infected donors.
A type of transplant that is suspected to spread the CJD is the corneal implant (a partial or complete transplantation of the cornea of the eye), which makes scientists believe that the eye is an important hiding place for prions. Many people with CJD develop vision problems and support that theory. And previous research has already found evidence of prions in the retina and optic nerve.
But the researchers behind this latest research wanted to look for prions through another test method that has become the gold standard for detecting prions in recent years, the RT-Quic. In contrast to older methods, the RT-Quic searches directly for the presence of incorrectly folded prions in a test sample, using a fluorescent dye. And now the accuracy of the test when diagnosing CJD is more than 90 percent.
They tested samples of eye tissue donated by 11 people who died from sCJD. In all 11 people the highest level of prions was seen in the retina. But prions were also spread across the cornea, the lens and other muscles in and around the eye. According to the researchers, it is their first study to detect prions in these other parts of the eyes.
The findings, which were published in mBio on Thursday, confirm the need for ophthalmologists to be particularly cautious in treating people who might have CJD, according to senior author Christina Sigurdson, a pathologist at the University of California, San Diego.
"Surgeons could unconsciously infect their instruments with prions," she said in a statement.
The best way to prevent transmission would be for ophthalmologists to use disposable equipment, but if this does not happen, it is necessary to decontaminate these tools between applications, because prions can survive sterilization techniques that would kill bacteria and viruses, such as radiation, formaldehyde. and extreme heat (only used).
The study also adds more incentives for the development of synthetic corneas cultivated in laboratories that can be used instead for transplants. There are only two documented cases of CJD that were probably caused by corneal grafts, but according to the researchers, the procedure is becoming increasingly popular, increasing the very small but real risk of future incidents. In general, about 350 Americans annually develop every form of CJD.
Nevertheless, there are a few positive takeaway moments from the study. The team found levels of prions in the retina that were almost as high as what they could find in the brain. This could mean that we can adapt or create non-invasive tests for CJD that simply rely on the eye. As things stand, doctors often diagnose CJD in a living person by testing their spinal fluid, which can only be obtained by an intensive, sometimes painful epidural.
"It really suggests that we could develop a diagnostic, eye-based test," Sigurdson said.
Sigurdson and her team are already working to develop new diagnostic tests for prion diseases. They also hope to further investigate the role of the eye at CJD, such as whether the tears of a person can carry prions.