Final answer:
Classical CJD typically does not involve lymphoid tissue, whereas vCJD does, which allows for potential human-to-human transmission through blood transfusions or contaminated medical procedures.
Step-by-step explanation:
Classical Creutzfeldt-Jakob Disease (CJD) and variant CJD (vCJD) are both prion diseases but differ in their presentations and pathologies. In classical CJD, prions are typically limited to the central nervous system and the presence of abnormal prion protein is usually not detected in lymphoid tissue. Contrastingly, in vCJD, abnormal prion protein is present in the lymphoid tissues. This presence in lymphoid tissues in vCJD allows the disease to be potentially transmitted through blood transfusions or contaminated surgical instruments. Diagnostic approaches for these diseases include the histological examination of brain tissue and assays such as RT-QuIC, which can detect abnormal prion proteins. While there is no cure for prion diseases, treatments aim to slow progression and maintain patient comfort.