Transmissible spongiform encephalopathies or TSEs are a group of fatal, rare, progressive neurological disorders that occur in humans and animals. TSEs are also referred to as prion diseases. The word prion is derived from the phrase proteinaceous infectious particle. Prions occur in both a normal form, which is a harmless protein that resides throughout the body, but have a higher concentration in the brain and nerve tissue, and in infectious forms, which cause disease. Prion disease is believed to result when normal prion proteins fold into an abnormal shape capable of causing other normal prions to misfold. The abnormal prion proteins accumulate causing a spongy brain tissue degeneration resulting in progressive dementia, visual and motor disturbances, difficulty swallowing, behavioral changes, and death.
The most common TSE affecting humans is Creutzfeldt-Jakob Disease (CJD). CJD falls into 4 subtypes: sporadic (spontaneous), familial (genetic/inherited), iatrogenic (inadvertent transmission via medical/surgical procedure), and variant.
Sporadic CJD is not related to Mad Cow Disease. Mad Cow Disease is a bovine TSE known as Bovine Spongiform Encephalopathy (BSE). The human-acquired TSE linked to the ingestion of beef from cows with BSE is a different clinical and pathological disease known as variant CJD (vCJD).
CJD occurs worldwide with an incidence ranging between 0.5 and 1.5 cases per million people per year.
Sporadic CJD (sCJD) accounts for greater than 85% of all CJD cases, familial CJD accounts for 10-15% of all cases, and iatrogenic CJD accounts for less than 5% of all CJD cases. vCJD is extremely rare. To date, there have been three cases of vCJD in the United States–two due to exposure in the United Kingdom and one due to exposure from Saudi Arabia. There have not been any domestically acquired vCJD cases in the United States.
- The mode of transmission for sporadic CJD is not known
- Familial CJD is an inherited condition and is very rare
- Iatrogenic CJD infection is inadvertently transmitted, usually from a person with sCJD to someone else in the course of medical/surgical treatment through the use of instruments in contact with infected brain issue or transplant of infected tissue itself
- Variant CJD, first recognized in the United Kingdom in 1996, is associated with bovine spongiform encephalopathy (BSE) or Mad Cow Disease. The exact route of transmission from BSE to humans is unknown but is believed that vCJD in humans results from the consumption of BSE infected cattle products
There is no evidence of person-to-person transmission of either vCJD or sCJD by casual contact or by the airborne/respiratory route. Central nervous system tissues are infectious throughout symptomatic illness. Other tissues and CSF may also be infectious. Infectivity during the incubation period is not known, but animal studies suggest that lymphoid and other organs are probably infectious before signs of illness appear. In very rare circumstances, sCJD has been acquired by contaminated neurosurgical instruments, transplantation of central nervous system tissue (corneal grafts and dura mater grafts), peripheral administration of human-derived pituitary hormones, and possibly for vCJD only, in transfused blood.
The incubation period for sporadic CJD is unknown. For iatrogenic CJD it varies by route of exposure from 15 months to > 30 years. For vCJD the incubation period is unknown but it is estimated to be 10 to 20+ years. Once symptoms begin, the disease is rapidly progressive and usually results in death within months up to a maximum of about 2 years.
Signs and Symptoms
There are broad similarities between all forms of CJD involving neurological and psychiatric problems that get progressively worse. Typically patients have problems with dementia that rapidly worsens as well as difficulties with walking and movement. However, the precise symptoms and course do differ between types of the disease.
The variant form differs from the sporadic form of CJD in the age distribution of affected patients, duration of illness, clinical manifestation and course, as well as the pathologic lesions in the brain and biochemical characteristics of the agent.
Symptoms and type of disease
Sporadic CJD – Is characterized by spontaneous onset of rapidly progressive dementia, sudden, involuntary jerking of a muscle or group of muscles (myoclonus), visual disturbance, tremors, rigidity, balance and difficulties with coordination, spasticity, inability to speak (akinetic mutism). The disease course is rapid and death typically occurs within 6 months after disease onset. Age at onset in sCJD cases is usually greater than 60 years of age.
Familial CJD – In general, the symptoms of the familial form of CJD are similar to those of sporadic CJD. Often familial CJD is diagnosed at an earlier age (around 50 years of age), has a later onset of dementia and a longer course of illness (6 to 36 months) than is typical for sCJD. DNA analysis on blood or brain tissue can be done to test for the presence of a genetic mutation. This test can only determine if a case has a familial prion disease. The National Prion Disease Pathology Surveillance Center does genetic testing for fCJD.
Variant CJD – Usually afflicts younger people (less than 55 years of age) and has a longer duration of illness (median duration of 12-14 months). Symptoms of vCJD are typically characterized as psychiatric or behavioral changes (psychosis, depression, anxiety, agitation, auditory or visual hallucinations), sensory pain in the extremities or other areas not related to injury or stimulation, lack of coordination and involuntary movements, and progressive dementia.
There is currently no established treatment to prevent sporadic or familial CJD or cure for any form of CJD. There are medications that may relieve symptoms and make the patient more comfortable. The current treatments are supportive.