The good news: researchers have found prions, the infectious agent for mad cow disease – more politely and correctly known as Creutzfeldt-Jakob disease – in the eyes of patients killed by the affliction. This opens the way to diagnosing the disease early.
The bad news: this means infected eyes are a possible biohazard, and the disease could be transmitted during eye exams. This may lead to the introduction of single-use instruments in ophthalmological clinics.
It was already known that corneal grafts on at least two occasions had spread infection. Plus there was the curious fact that about 40 per cent of people with CJD developed eye problems – often early in the course of their illness.
The retinas especially prone to infection
This led researchers from the National Institutes of Health and the University of California San Diego School of Medicine, to study the eyes of 11 deceased people with sporadic or non-genetic Creutzfeldt-Jakob disease (sCJD). This week in mBio, they reported finding prion seeds – the infectious proteins that cause the disease – spread throughout the eyes of all the patients.
Prions are misshapen forms of a normally harmless protein. It is not known what causes the normal prion protein to mis-fold and become pathogenic. In humans, prions accumulating in the brain produce lesions that can lead to rapidly progressive neuro-degeneration.
The highest level of prions was found in the retina – comparable to the extent they are found in the brain. But prions were also discovered throughout the cornea, lens, and other muscles in and around the eye. The researchers say this was the first time prions have been detected in these other parts of the eye.
Call for new decontamination protocols
Consequently, the researchers have recommended that ophthalmology exams employ either single-use instruments or equipment decontamination procedures to eliminate risk of prion transmission from patient to patient.
They also hoped the findings would spur greater efforts to develop corneal grafting techniques, such as biosynthetic corneas, to eliminate accidental disease transmission.
Lead author Christina J. Sigurdson, professor of pathology at UC San Diego and UC Davis, said in a statement on the UC San Diego website: “Almost half of sCJD patients develop visual disturbances, and we know that the disease can be unknowingly transmitted through corneal graft transplantation.
“But distribution and levels of prions in the eye were unknown. We’ve answered some of these questions. Our findings have implications for both estimating the risk of sCJD transmission and for development of diagnostic tests for prion diseases before symptoms become apparent.”
By the time Creutzfeldt-Jakob disease is diagnosed, patients usually have less than a year to live. In fact, it’s only when the patient has died that diagnosis is confirmed by testing a sample of brain tissue.
The probable diagnosis of living patients is done by measuring the brain’s electrical activity, brain scans or testing for prions prions in the cerebrospinal fluid via painful spinal tap.
The reason why diagnosis is difficult and tends to come late is because Creutzfeldt-Jakob disease can cause a variety of symptoms that resemble those of other, more common conditions. These include anxiety, depression, memory loss, personality changes, vision problems, insomnia, impaired thinking and problems with muscle coordination.
Creutzfeldt-Jakob disease is rare, literally one in a million becomes infected. Ten to 15 per cent of sufferers inherit the disease via a genetic mutation. Most have sporadic Creutzfeldt-Jakob disease which is transmitted by exposure to the brain or nervous system tissue, usually through certain medical procedures. Rare cases involve persons eating meat from cattle affected by a disease similar to CJD called bovine spongiform encephalopathy or “mad cow disease”.
The best known example of person-to-person transmission of CJD occurred among the Fore tribe of Papua New Guinea when the women and children practised the ritual of eating the brains of deceased loved ones. They gave it the name kuru meaning “to shake”. When the ritual ceased being observed in the 1960s, the disease was eradicated.