What is the "zombie deer" virus? ——What is "prion disease"?

What is prion disease?

Recently, the United States reported that the "zombie deer" virus was detected in Yellowstone Park, which has attracted attention. What exactly is the "zombie deer" virus? "Zombie deer" is the manifestation of prion infection in animals . Although it is called a virus, prions are essentially a protein that can infect a variety of animals (sheep, cattle, deer, camels, etc.) and humans . In fact, as early as 1969, the United States had detected the existence of prions in captive deer.

Prion disease is a type of degenerative disease caused by prions (abnormally shaped proteins) that invades the central nervous system of humans and a variety of mammals. It has a long incubation period and a 100% mortality rate .

Prion diseases in humans are mainly divided into Creutzfeldt-Jakob disease (sporadic, hereditary, iatrogenic, variant, CJD), kuru , Gerstmann syndrome (GSS), and fatal familial insomnia (FFI). The incidence of human prion diseases in most developed countries is 1 to 1.5 cases per million people per year.

Among human prion diseases, 80%-95% are sporadic CJD . The average survival of patients with sporadic CJD is about 6 months , and 85%-90% of patients die within 1 year. The peak age of onset is 55-75 years old . The following is a brief introduction to the basic situation of CJD, taking CJD as an example.

There are three main mechanisms of prion disease in humans:

There are spontaneous (sporadic CJD), inherited (hereditary CJD) and acquired (iatrogenic CJD, variant CJD). 85-90% of CJD cases are sporadic .

In sporadic CJD, conversion of normal prion protein (PrPC) to diseased prion protein (PrPSc) is thought to occur spontaneously (or possibly through somatic mutation of PRNP ).

Hereditary Creutzfeldt-Jakob disease is more likely to come from the genes carried by the family, which makes the prion protein gene PRNP more susceptible to mutations.

Iatrogenic CJD infection occurs iatrogenically via corneal transplantation, EEG depth electrodes, etc.

Variant CJD is the only human prion disease known to be transmitted directly from animals to humans and is caused by eating beef products infected with mad cow disease.

The histopathological changes of CJD include neuronal cell loss, gliosis, vacuolization (formerly known as spongiform changes), and PrPSc protein deposition. Because the lesions mainly occur in neurons, most cases of CJD will show progressive dementia , pyramidal/extrapyramidal dysfunction , visual or cerebellar disorders, etc.

The gold standard for diagnosing CJD is to detect PrPSc protein in the patient's brain tissue . Because brain tissue samples are difficult to obtain, they can usually only be collected after the patient dies.

Clinically, whether a patient is a clinically diagnosed case of CJD is mainly determined based on the patient's clinical manifestations, EEG changes, MRI changes, and pathological changes.

Although some symptoms of human prion disease can be temporarily treated, unfortunately, three randomized double-blind placebo-controlled trials failed to change the outcome of the disease, and there is currently no cure . According to domestic patient follow-up data, most patients die within 6 months of onset .

Source: Beijing Center for Disease Control and Prevention official account