healthHealth and Medicine

Rare Brain-Eroding Prion Disease Is On The Increase In Japan


Tom Hale

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist


An artist's impression of a prion. StudioMolekuul/

Once a rarity, an increasing number of people in Japan are falling chronically ill with a deadly brain disease caused by rogue misfolding proteins. Researchers strongly suspect this is a symptom of the country’s “hyper-aging” population, but it's looking like this trend could soon become a problem in many other parts of the world too. 

As reported in the journal Scientific Reports in September, scientists at Okayama University looked at the number of deaths and incidence rates associated with Creutzfeldt-Jakob disease (CJD) in Japan between 2005 and 2014. They concluded that the number of people with CJD doubled within that time frame, increasing by around 6.4 percent each year. 


CJD is an extremely rare and deeply unusual disease that affects the brain, causing symptoms such as depression, memory problems, behavioral changes, poor coordination, and visual disturbances. The disease is also fatal and there are currently no treatments. 

It's not caused by viruses, bacteria, fungi, or parasites, but something known as a prion, an infectious misfolded protein that’s able to corrupt and misfold other normal proteins. Once a prion finds itself in the brain, it starts a domino effect on nearby proteins and turns them into prions, resulting in the brain tissue eroding away. Under a microscope, the brain tissue of a person or animal with a prion disease shows a distinctive spongy appearance, caused by tiny holes where cells have died. Unlike most other infectious agents, prions are not inactivated by heat, ultraviolet light, or any other standard sterilization procedures, making them extremely difficult to deal with.  

Almost 30 percent of the population in Japan is aged 65 years or older. Pasakorn Hansetagan/

Some prion diseases can be picked up by consuming the brain tissue of an infected individual or animal. One of the major breakthroughs in the discovery of prion diseases occurred when a scientist-explorer came across an unusual disease in a tribe of people who practiced cannibalism in Papua New Guinea. There are also a handful of unusual case reports of people contracting the illness after eating infected tissue, such as squirrel brains. 

Perhaps the best-known incident involving prions is the UK BSE outbreak in the 1980s and '90s in which over 175 people died after contracting variant Creutzfeldt–Jakob disease (vCJD) through eating infected beef, giving it the nickname "mad cow disease". It’s believed that the cattle had become infected with the prions after being fed meat and bone meal that had been contaminated with brain tissue.


However, sketchy meat is not suspected to be a major factor in Japan’s rising number of CJD cases. Up to 85 percent of the cases identified in the report is a form of the disease called sporadic CJD (sCJD), which almost always occurs in the elderly. Scientists aren’t totally sure what causes this form of the disease, but it’s believed to be associated with the effects of aging on cellular machinery. In other words, older people are more likely to produce faulty proteins that are prone to become prions. 

Since sCJD primarily affects people over the age of 60, the researchers argue that the increased prevalence of the disease in Japan is simply a reflection of its aging population; 28 percent of the population is aged 65 years or older. Nevertheless, they warn that this trend is unlikely to stay in Japan since most countries now have a rising life expectancy and an aging population.

“Despite CJD being a rare disease, the phenomenon of population aging may trigger a rise in the incidence and, thus, the socioeconomic and healthcare burden of CJD. Our aim was to analyze these trends, in an effort to spread awareness and spur new treatment strategies," Dr Yoshito Nishimura, first author of the study, said in a statement“CJD, albeit rare, will be more prevalent in the next 5 to 10 years.” 


healthHealth and Medicine
  • tag
  • prion,

  • CJD,

  • creutzfeldt-jakob disease,

  • BSE,

  • mad cow disease,

  • Japan,

  • old age,

  • Variant Creutzfeldt-Jakob disease,

  • aging population