Final answer:
The nurse should inform the parents that since heat treatment began, there have been no reports of virus transmission since 1986.
Step-by-step explanation:
The nurse should respond with option D) "Since heat treatment began, there have been no reports of virus transmission since 1986."
This response provides accurate and reassuring information to the parents. Heat treatment of blood products has been used since 1986 to inactivate viruses such as hepatitis and HIV, greatly reducing the risk of transmission during transfusions. This information is based on scientific research and should help alleviate the parents' concerns.