<unk>  can be caused by immune disease or exposure to certain chemicals, drugs, radiation, or infection; in about half the cases, a definitive cause is unknown. It is not a hereditary condition, nor is it contagious.<unk>  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. However, the probability that these drugs will lead to<unk>  in a given patient is very low. Chloramphenicol treatment is associated with aplasia in less than one in 40,000 treatment courses, and carbamazepine aplasia is even rarer. Exposure to ionizing radiation from radioactive materials or radiation-producing devices is also associated with the development of<unk> . Marie Curie, famous for her pioneering work in the field of radioactivity, died of<unk>  after working unprotected with radioactive materials for a long period of time; the damaging effects of ionizing radiation were not then known.<unk>  is present in up to 2% of patients with acute viral hepatitis. One known cause is an autoimmune disorder in which white blood cells attack the bone marrow. Acquired<unk>  is a T-cell mediated autoimmune disease, in which regulatory T cells are decreased and T-bet, a transcription factor and key regulator of Th1 development and function, is upregulated in affected T-cells. As a result of active transcription of the interferon gamma (IFN-gamma) gene by T-bet, IFN-gamma levels are increased, which reduces colony formation of hematopoietic progenitor cells in vitro by inducing apoptosis of CD34+ cells in the bone marrow. Short-lived<unk>  can also be a result of parvovirus infection. In humans, the P antigen (also known as globoside), one of many cellular receptors that contribute to a person's blood type, is the cellular receptor for parvovirus B19, which causes erythema infectiosum (fifth disease) in children. Because it infects red blood cells as a result of the affinity for the P antigen, parvovirus causes complete cessation of red blood cell production. In most cases, this goes unnoticed, as red blood cells live on average 120 days, and the drop in production does not significantly affect the total number of circulating cells. However, in people with conditions where the cells die early (such as sickle cell disease), parvovirus infection can lead to severe anemia. More frequently, parvovirus B19 is associated with<unk>  crisis, which involves only red blood cells (despite the name).<unk>  involves all cell lines. Other viruses that have been linked to the development of<unk>  include hepatitis, Epstein-Barr, cytomegalovirus, and HIV. In some animals,<unk>  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.
Aplastic anemia
Acute lymphoblastic leukemia
Refractory anemia with excess of blasts
Polycythemia vera
Myelodysplastic syndrome
Myomatous erythrocytosis syndrome
Essential thrombocythemia
Refractory cytopenia of childhood