Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Creutzfeldt-Jakob disease ?
    ### Response:
    What causes Creutzfeldt-Jakob disease? Some researchers believe an unusual 'slow virus' or another organism causes Creutzfeldt-Jakob disease (CJD). However, they have never been able to isolate a virus or other organism in people with the disease. Furthermore, the agent that causes CJD has several characteristics that are unusual for known organisms such as viruses and bacteria.
    