Creutzfeldt-Jakob Disease (CJD, Classic), Variant Creutzfeldt-Jakob Disease (vCJD), and Bovine Spongiform Encelphalopathy (BSE, aka. Mad Cow Disease) are several forms of a prion disease that are often referred to as being the same disease, however this is not accurate.
Classical Creutzfeldt-Jakob Disease (CJD) is a rare, fatal brain disorder, which causes a rapid, progressive dementia and associated neuromuscular disturbances. CJD is usually acquired in one of three ways. The disease can occur sporadically, i.e., without apparent cause; it can be inherited; or it can be transmitted from an infected person through corneal transplants, implantation of electrodes in the brain, dura mater grafts, contaminated surgical instruments, and the injection of human growth hormone derived from cadaveric pituitaries, as well as the injection of human pituitary gonadotrophin.
Variant Creutzfeldt-Jakob Disease (vCJD) differs from classical CJD in some important ways. First of all, classical CJD almost always affects persons older than 60 years of age, while vCJD has been found in persons much younger. Secondly, vCJD often presents with behavioral problems, while classical CJD presents with dementia and movement disorders. Patients with classical CJD have typical findings on electroencephalography (EEG) testing, whereas those with vCJD do not. Finally, vCJD progresses less rapidly (however, both diseases are fatal).
Bovine Spongiform Encelphalopathy (BSE) is a progressive neurological disorder of cattle, often referred to as "Mad Cow Disease", that results from infection by an unusual transmissible agent called a prion. The nature of the transmissible agent is not well understood. Currently, the most accepted theory is that the agent is a modified form of a normal protein known as prion protein. For reasons that are not yet understood, the normal prion protein changes into a pathogenic (harmful) form that then damages the central nervous system of cattle.