Prion diseases are a group of rare neurodegenerative disorders that can affect both humans and animals.

They’re caused by abnormally folded proteins in the brain, particularly the misfolding of prion proteins (PrP).

This leads to a progressive decline in brain function, involving changes in memory, behavior, and movement. Eventually, prion diseases are fatal.

Around 300 new cases of prion disease are reported each year in the United States.

They can be:

  • Acquired through contaminated food or medical equipment
  • Inherited via mutations in the gene that codes for PrP
  • Sporadic, where the misfolded PrP develops without any known cause

In people with prion disease, the misfolded PrP can bind to healthy PrP, which causes the healthy protein to also fold abnormally.

Misfolded PrP begins to accumulate and form clumps within the brain, damaging and killing nerve cells.

This damage causes tiny holes to form in brain tissue, making it appear sponge-like under a microscope. (That’s why you may see prion diseases referred to as “spongiform encephalopathies.”)

Researchers are still working to understand more about prion diseases and find an effective treatment. But they do know some things.

Read on to find out about the different types of prion disease, if there are any ways to prevent them, and more.

Prion disease can occur in both humans and animals. Below are some different types of prion diseases. More information about each disease follows the table.

Human prion diseasesAnimal prion diseases
Creutzfeldt-Jakob disease (CJD)Bovine spongiform encephalopathy (BSE)
Variant Creutzfeldt-Jakob disease (vCJD)Chronic wasting disease (CWD)
Fatal familial insomnia (FFI)Scrapie
Gerstmann-Straussler-Scheinker syndrome (GSS)Feline spongiform encephalopathy (FSE)
KuruTransmissible mink encephalopathy (TME)
Ungulate spongiform encephalopathy

Human prion diseases

  • Creutzfeldt-Jakob disease (CJD). First described in 1920, CJD can be acquired, inherited, or sporadic. Most cases of CJD are sporadic.
  • Variant Creutzfeldt-Jakob disease (vCJD). This form of CJD can be acquired through eating the contaminated meat of a cow.
  • Fatal Familial insomnia (FFI). FFI affects the thalamus, which is the part of your brain that manages sleeping and waking cycles. One of the main symptoms of this condition is worsening insomnia. The mutation is inherited in a dominant manner, meaning an affected person has a 50 percent chance of transmitting it to their children.
  • Gerstmann-Straussler-Scheinker syndrome (GSS). GSS is also inherited. Like FFI, it’s transmitted in a dominant manner. It affects the cerebellum, which is the part of the brain that manages balance, coordination, and equilibrium.
  • Kuru. Kuru was identified in a group of people from New Guinea. The disease was transmitted via a form of ritual cannibalism in which the remains of deceased relatives were consumed.

Risk factors for these diseases include:

  • Genetics. If someone in your family has an inherited prion disease, you’re at an increased risk of having the mutation, too.
  • Age. Sporadic prion diseases tend to develop in older adults.
  • Animal products. Consuming animal products that are contaminated with a prion can transmit a prion disease to you.
  • Medical procedures. Prion diseases can be transmitted through contaminated medical equipment and nervous tissue. Cases where this has happened include transmission through contaminated cornea transplants or dura mater grafts.

Animal prion diseases

  • Bovine spongiform encephalopathy (BSE). Commonly called “mad cow disease,” this type of prion disease affects cows. Humans who consume meat from cows with BSE can be at risk for vCJD.
  • Chronic wasting disease (CWD). CWD affects animals like deer, moose, and elk. It gets its name from the drastic weight loss observed in sick animals.
  • Scrapie. Scrapie is the oldest form of prion disease, having been described as far back as the 1700s. It affects animals like sheep and goats.
  • Feline spongiform encephalopathy (FSE). FSE affects domestic cats and wild cats in captivity. Many of the cases of FSE have occurred in the United Kingdom, with some also seen in other parts of Europe and Australia.
  • Transmissible mink encephalopathy (TME). This very rare form of prion disease affects mink. A mink is a small mammal that’s often raised for fur production.
  • Ungulate spongiform encephalopathy. This prion disease is also very rare and affects exotic animals that are related to cows.

Diseases caused by prions

The prion diseases highlighted above aren’t the only diseases linked to prions.

Other neurodegenerative diseases, like Alzheimer’s and Parkinson’s, are also associated with misfolded proteins in the central nervous system. And research has found that some of these misfolded proteins may be prions.

But some scientists believe that these proteins only act in a prion-like way. They argue that they can’t be prions as the diseases they cause, like Alzheimer’s, aren’t thought to be infectious.

Prion diseases have very long incubation periods, often on the order of many years. When symptoms develop, they progressively worsen, sometimes rapidly.

Common symptoms of prion disease include:

There’s currently no cure for prion disease. But treatment focuses on providing supportive care.

Examples of this type of care include:

  • Medications. Some medications can be prescribed to help treat symptoms. Examples include:
    – reducing psychological symptoms with antidepressants or sedatives
    – providing pain relief using opiate medication
    – easing muscle spasms with drugs like sodium valproate and clonazepam
  • Assistance. As the disease advances, many people need help taking care of themselves and performing daily activities.
  • Providing hydration and nutrients. In advanced stages of the disease, IV fluids or a feeding tube may be required.

Scientists continue to work to find an effective treatment for prion diseases.

Some of the potential therapies being investigated include the use of anti-prion antibodies and “anti-prions” that inhibit the replication of abnormal PrP.

Since prion diseases can present similar symptoms to other neurodegenerative disorders, they can be difficult to diagnose.

The only way to confirm a diagnosis of prion disease is through a brain biopsy performed after death.

But a healthcare professional can use your symptoms, medical history, and several tests to help diagnose prion disease.

The tests they may use include:

  • MRI. An MRI can create a detailed image of your brain. This can help healthcare professional visualize changes in brain structure that are associated with prion disease.
  • Cerebrospinal fluid (CSF) testing. CSF can be collected and tested for markers associated with neurodegeneration. In 2015, a test was developed to specifically detect markers of human prion disease.
  • Electroencephalography (EEG). An EEG records electrical activity in your brain. Abnormal patterns can occur with prion disease, particularly with CJD, where short periods of increased activity may be seen.

Several measures have been taken to prevent the transmission of acquired prion diseases. Because of these proactive steps, acquiring a prion disease from food or a medical setting is now extremely rare.

Some of the preventive steps taken include:

  • setting tight regulations on importing cattle from countries where BSE occurs
  • prohibiting parts of the cow like the brain and spinal cord from being used in food for humans or animals
  • preventing those with a history of or risk for exposure to prion disease from donating blood or other tissues
  • using robust sterilization measures on medical instruments that have come into contact with the nervous tissue of someone with suspected prion disease
  • destroying disposable medical instruments

There’s currently no way to prevent inherited or sporadic forms of prion disease.

If someone in your family has an inherited prion disease, you may consider consulting with a genetic counselor to discuss your risk of developing the disease.

Prion diseases are a rare group of neurodegenerative disorders caused by abnormally folded proteins in your brain.

The misfolded protein forms clumps that damage nerve cells, leading to a progressive decline in brain function.

Some prion diseases are genetically transmitted, while others can be acquired through contaminated food or medical equipment. Other prion diseases develop without any known cause.

There’s currently no cure for prion diseases. Instead, treatment focuses on providing supportive care and easing symptoms.

Researchers continue to work to discover more about these diseases and to develop potential treatments.