(NewsNation) — Scientists in China are reportedly experimenting with a mutant COVID strain with a 100% kill rate in mice.

This strain attacks the brains of the mice, which are engineered to reflect a genetic makeup similar to that of humans. 

Most mice in the experiment lived only eight days after being infected. The animals lost weight, became sluggish, adopted a hunched posture, and their eyes turned completely white in the days before their death. 

Still, experts told NewsNation the study is small and that the paper has not been peer-reviewed yet, meaning there is no cause for alarm.

But there are other diseases with fatality rates of 100%, or very close to it, though these tend to be rare and are usually passed down through genetics.

Some of them include:

Creutzfeldt–Jakob disease

Creutzfeldt–Jakob disease, the CDC writes, is an “always fatal” neurodegenerative disorder that progresses rapidly. Deaths usually occur within a year of the illness’ onset, with many dying because of medical issues associated with Creutzfeldt-Jakob.

Characterized as a “prion disease,” Creutzfeldt–Jakob is described by the Mayo Clinic as similar to Alzheimer’s. It can involve changes in mental abilities, personality changes, memory loss, impaired thinking, blindness, insomnia, problems with coordination, speaking and swallowing issues and “sudden, jerky movements.” About one in one million people in the United States are reported to have Creutzfeldt-Jakob every year.

Fatal Familial Insomnia

The Cleveland Clinic calls fatal familial insomnia a “rare genetic condition” affecting the brain and central nervous system. 

Those affected may have trouble sleeping, memory loss and muscle twitching. Considered a “degenerative” disease, these symptoms increase in severity over time. There is currently no cure, but researchers are studying how to reduce the symptoms’ progression and how to possibly extend the lives of people diagnosed with fatal insomnia, the clinic writes.

Between one and two out of 1 million are diagnosed with fatal familial insomnia every year. It is genetic, with 50 to 70 families worldwide carrying the mutation causing familial insomnia, the Cleveland Clinic said. 

There are “extremely rare” cases where FFI happens in people without a history of it in their family because of a genetic mutation. 

Treatment is more about relieving symptoms and making the person suffering from FFI comfortable as opposed to actually curing it. 

Kuru

Kuru, a rare and fatal brain disorder, was at epidemic levels from the 1950s through the 1960s among the  Fore people in the highlands of New Guinea because of their practice of ritualistic cannibalism.

During these rituals, relatives of deceased family members would prepare and consume their tissues, including that of the brain, according to the National Institute of Neurological Disorders and Stroke. Brain tissue from those with kuru is highly infectious, and the disease is transmitted further through eating it or with contact through open sores or wounds. Because of government discouragement of cannibalism, there was a continuing decline in the disease, and NINDS says it has now “mostly disappeared.”

Other than not engaging in cannibalism, there are no other treatments for controlling or curing kuru. The disease does have a long incubation period, with some not showing symptoms for years or even decades. An unsteady gait, tremors and slurred speech are usually the first symptoms, though NINDS notes that dementia was either “minimal or absent” in most cases. Mood changes often happened, though, and individuals with kuru became unable to stand or eat and died in a comatose state six months to a year after symptoms first started. 

Gerstmann–Sträussler–Scheinker syndrome

Similar to other diseases on this list, Gerstmann–Sträussler–Scheinker syndrome is also a neurodegenerative brain disorder that is almost only inherited. Extremely rare, it is only found in a few families around the world, according to NINDS.

Most people who get it will be between the ages of 35 and 55 and experience varying levels of lack of muscle coordination, with many developing dementia. Other symptoms, NINDS said, are slurred speech, involuntary eye movements, rigid muscle tone and visual disturbances that in some cases lead to blindness.

There is no cure for GSS nor are there any known treatments to slow progression of the disease. Current therapies are aimed at alleviating symptoms. GSS is a slowly progressive condition usually lasting from two to 10 years. The disease ultimately causes severe disability and death.

Rabies

Rabies, likely the most well-known of the highly rated diseases, is almost always fatal, with less than 20 cases of human survival from it reported, according to the CDC.

When exposed to rabies, the virus has to travel to the brain before it causes symptoms, though it could take weeks to months for them to show. 

Symptoms mirror the flu, such as weakness, discomfort, fever and headache. Discomfort, prickling or an “itching sensation” might be felt where the person was bitten. 

Eventually, symptoms progress to cerebral dysfunction, anxiety, confusion, and agitation, and the person affected could experience delirium, abnormal behavior, hallucinations, hydrophobia and insomnia. 

The CDC says only one to three human rabies cases are reported yearly.  

NewsNation correspondent Brian Entin contributed to this article.