Final answer:
Classic CJD primarily includes sporadic CJD with no identifiable cause and hereditary forms due to genetic mutations. It differs from vCJD, which is associated with mad cow disease and can be transmitted among humans via contaminated blood or tissue.
Step-by-step explanation:
Classic forms of Creutzfeldt-Jakob Disease (CJD) mainly include the sporadic CJD, which accounts for approximately 85% of CJD cases and has no identifiable cause. There are also hereditary forms, which result from a genetic mutation and can be familial. It's important to differentiate these from variant CJD (vCJD), which is linked to consumption of meat from animals affected by Bovine Spongiform Encephalopathy (BSE or mad cow disease) and has documented transmission from human to human via blood transfusions or consumption of contaminated nervous tissue. In the case of classic CJD, human-to-human transmission can occur through exposure to infected brain or nervous system tissue, for instance, via medical procedures using contaminated surgical instruments. Both classic and variant forms are fatal neurodegenerative diseases caused by prions, which induce the misfolding of normal cellular proteins, leading to the characteristic brain damage seen in afflicted patients.