The current recommendation in the industry is that a woman infected with HIV or Hepatitis B or C should not consume their placenta. Because of the health hazards involved, the hospital would probably not be legally allowed to release a placenta in these circumstances.
I do know, however, that HIV is ridiculously easy to kill and the steaming process would effectively kill the virus present in the placenta. I also know the cleaning methods and standards of sanitation involved in the encapsulation process are effective against blood borne pathogens. With these two thoughts, if I were HIV positive and had my baby at home as I choose to do anyway, I would probably keep my placenta and encapsulate it. I would be willing to assume any risks associated with that decision.
So, my point is that if you you have a blood borne illness but feel strongly about encapsulating your placenta, then do your research. Learn about your illness and decide if you feel it really should exclude you from encapsulating. Decide where your comfort level is and if it is something feasible for you.