Is aplastic anemia caused by a virus?

This, indeed, is the case, and was true for your client as well. Medical research has provided many clues pointing to this, including the association of aplastic anemia in those with a history of infection by a variety of viruses, that it somehow weakens their immune system and allows an autoimmune attack that seemingly damages the bone marrow precursors that become circulating blood cells. There is a kind of scientific blind spot keeping medicine from understanding the large group of autoimmune diseases, that there is an actual pathogen the body is fighting, and the collateral damage to normal cells is not autoimmune but an innocent bystander inevitability, as a consequence of the power of the immune system to wage war. Medicine does not realize that warfare is appropriate because there is an enemy attacking in the form of pathogenic organisms that need to be repelled. The fact that viruses are so difficult to detect directly, has resulted in this arena neglecting what would be the most rewarding avenue for research into the true causes.