There are a whole list of things they ask when you donate blood, including if you've ever been diagnosed with hepatitis, any STD, TB, malaria - and this includes HIV. All of these leave residual antibodies in the blood, which can (as in hepatitis and HIV) transmit the disease to someone else. Or, as with malaria or many STDs, just leave weird antibodies that someone with a compromised immune system might get ill from - as in someone receiving blood transfusions.
When I had schisto mansoni (a blood fluke, got it in Liberia, goes and messes up your liver) I was told NEVER to donate organs or blood - not that I would give someone the parasite, because we killed them - but because I have weird schisto antibodies in my organs and my blood and it could make someone sick. As in, REALLY sick.
However, medicine keeps changing, and there's always the possibility that some day these blood-born diseases can be cleaned out of someone's blood and the blood can be used.
"Dance as if no one is watching."
| Pounds lost: 45.0