Final answer:
Hepatitis B and Hepatitis C viruses are the ones identified with spread through unscreened blood transfusions. Both are blood-borne viruses with the capability of long-term persistence and transmission via parenteral contact.
Step-by-step explanation:
The Hepatitis B (HBV) and Hepatitis C (HCV) viruses have been scientifically identified as being spread by the transfusion of unscreened blood products. HBV is a double-stranded DNA virus that uses reverse transcriptase for replication and belongs to the Hepadnavirus family. HCV, on the other hand, is a single-stranded RNA virus from the Flavivirus family. Both of these viruses are primarily transmitted through parenteral contact, which includes unscreened blood transfusions and the sharing of needles. HCV is often undiagnosed, leading to a higher spread through blood transfusions before widespread blood product screening was implemented. HBV can also be transmitted through other body fluids and can remain infective on surfaces for up to seven days. Hepatitis D (HDV) is also blood-borne but requires co-infection with HBV to propagate.