Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Hemorrhagic Fevers ?
    ### Response:
    Viral hemorrhagic fevers (VHFs) are a group of illnesses caused by four families of viruses. These include the Ebola and Marburg, Lassa fever, and yellow fever viruses. VHFs have common features: they affect many organs, they damage the blood vessels, and they affect the body's ability to regulate itself.
    