Transmissible spongiform encephalopathies (TSE) are a group of rare, fatal diseases that cause rapidly progressive dementia. They have long incubation periods and many years and even decades may pass between the time of infection and the first signs and symptoms of the disease. TSEs have been linked to certain types of proteins called prions. It is believed that when these prions become infectious, they kill nerve tissues (e.g., brain cells) with which they come into contact. According to the National Institutes of Health, TSE occur in about one person per million each year, worldwide. Within the United States, there are about 300 cases per year.

There are several different types of TSE. Some of these affect animals, and some affect humans. The most common human TSE is Creutzfeldt-Jakob disease (CJD). A similar but distinct condition, variant Creutzfeldt-Jakob disease (vCJD), has been linked to the consumption of meat contaminated by bovine spongiform encephalopathy (BSE), or mad cow disease. Other TSEs that may affect humans include Gerstmann-Straussler-Scheinker disease, fatal familial insomnia and kuru.

Most TSEs tend to occur in older individuals. According to the National Institute of Neurological Disorders and Stroke (NINDS), symptoms of CJD tend to first occur around age 60. After symptoms are present, about 90 percent of patients die within 12 months. On the other hand, variant CJD is known to affect younger individuals. According to the Centers for Disease Control and Prevention (CDC), the average age at death for people with this disease is about 29.

In most cases, TSEs spontaneously occur in individuals with no known risk factors (sporadic disease). According to both NINDS and the CDC, about 85 percent of CJD cases occur in this manner. Some cases of TSE may also be hereditary. According to the CDC, about 5 percent to 15 percent of all cases of CJD are inherited. TSEs can also be acquired from other humans. However, this is very rare. According to NINDS, less than 1 percent of all known cases of CJD have been acquired. The only human TSE positively linked to food contamination is vCJD.

Most TSEs have similar symptoms, although the severity of certain symptoms may be greater in one form than in another. The first symptoms of many TSEs are psychiatric problems (e.g., depression, anxiety, insomnia). Eventually, neurological signs (e.g., unpleasant sensations, problems walking, lack of coordination, vision problems) develop. Patients also begin to feel confused, forgetful, and have difficulty thinking and speaking. In later courses of the diseases, patients become unable to speak or move and enter a coma. All TSEs are ultimately fatal.

The only ways to positively diagnose TSEs are by means of a brain biopsy (an invasive and risky procedure) or autopsy. However, a probable diagnosis can be made from the patient’s medical history, signs and symptoms, magnetic resonance imaging (MRI) of the brain and an electroencephalogram (EEG).

There are no known methods to cure TSEs, so current treatment is aimed at making the patient feel as comfortable as possible. While TSEs cannot always be prevented, precautions can be taken to reduce the risks. This is especially true for vCJD. The United States, United Kingdom and many other countries have put several strict regulations in place for the purpose of stopping the spread of BSE and preventing vCJD.