Causes
In many cases, the etiology is considered to be idiopathic (without a known cause), but one known cause is an autoimmune disorder in which white blood cells attack the bone marrow.
Aplastic anemia is also sometimes associated with exposure to toxins such as benzene, or with the use of certain drugs, including chloramphenicol, carbamazepine, felbamate, phenytoin, quinine, and phenylbutazone. Many drugs are associated with aplasia mainly according to case reports, but at a very low probability. As an example, chloramphenicol treatment is followed by aplasia in less than one in 40,000 treatment courses, and carbamazepine aplasia is even more rare.
Exposure to ionizing radiation from radioactive materials or radiation-producing devices is also associated with the development of aplastic anemia. Marie Curie, famous for her pioneering work in the field of radioactivity, died of aplastic anemia after working unprotected with radioactive materials for a long period of time; the damaging effects of ionizing radiation were not then known.
Aplastic anemia is present in up to 2% of patients with acute viral hepatitis.
In some animals, aplastic anemia may have other causes. For example, in the ferret (Mustela putorius furo), it is caused by estrogen toxicity, because female ferrets are induced ovulators, so mating is required to bring the female out of heat. Intact females, if not mated, will remain in heat, and after some time the high levels of estrogen will cause the bone marrow to stop producing red blood cells.
Short-lived aplastic anemia can also be a result of parvovirus infection. In humans, the P antigen (also known as globoside) is the cellular receptor for parvovirus B19 virus that causes erythema infectiosum (fifth disease) in children. Parvovirus causes complete cessation of red blood cell production. In most cases, this goes unnoticed, as red blood cells live up to 180 days, and the drop in production does not significantly affect the total number of circulating red blood cells. In people with conditions where the cells die early (such as sickle cell disease), however, parvovirus infection can lead to severe anemia.
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