Final answer:
The virus that was frequently transmitted through blood transfusions in the past is HIV, which causes AIDS. Improved blood screening has greatly reduced the risk of transmission through transfusions.
Step-by-step explanation:
The blood-borne virus that was frequently transmitted through blood transfusions in the past is the human immunodeficiency virus (HIV), which causes Acquired Immunodeficiency Syndrome (AIDS). In the 1980s and early 1990s, before blood was routinely screened for HIV, transfusions were a common way for the virus to spread. Individuals with hemophilia or those requiring transfusions were particularly at risk. However, after the implementation of rigid blood screening and testing protocols, the risk of transmission through transfusions has been greatly reduced, especially in high-income countries.
Additionally, hepatitis C is another blood-borne virus that was also commonly transmitted through blood transfusions before widespread screening began. Today, the safety of blood transfusions has significantly improved due to careful donor selection and blood screening practices. Infections such as the flu are not typically transmitted through blood, and while viral hemorrhagic fevers like yellow fever and Ebola virus disease can be spread through contact with infected blood, they were not predominantly spread through transfusions but are rather known to be arboviral diseases transmitted by vectors like mosquitoes.
The blood-borne virus frequently transmitted through blood transfusions in the past was HIV, the virus that causes AIDS. Thanks to improved screening measures, this risk is now significantly lowered.