Just Curious, What happens with contaminated blood?

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I have alway been interested in forensic science. I have a question. If someone has a horrible disease,cancer,diabetic, aides, etc. When they pass away amd they take out the blood. What do they do with it? I just wondered if this could be part of the disease epidemic of things that they don't know where they come from or how to treat them. Anyone else ever wonder about this?