Light micrograph of a section through a brain infected with variant Creutzfeldt-Jakob disease (vCJD) showing a loss of neurons (nerve cells), seen as white spaces. The disease is the result of virus-like prions within the brain that cause vacuoles and plaques to form, making the brain spongy and killing off the tissue. Symptoms include dementia and sudden muscle contractions, leading to death. The similarly fatal cattle disease BSE (bovine spongiform encephalopathy) has been linked to human vCJD.