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I/ HIV/AIDS /Epidemic/ 1/ General Back ground Human Immunodeficiency Virus, infectious agent that causes acquired immunodeficiency syndrome (AIDS), a disease that leaves a person vulnerable to life-threatening infections. Scientists have identified two types of this virus. HIV-1 is the primary cause of AIDS worldwide. HIV-2 is found mostly in West Africa.

2/How Immune Deficiency Diseases The immune system is composed of a collection of cells, specialized organs, and proteins in the blood that work together to defend against foreign substances, which enter the body from the external environment. A large number of genes are required to create the components of the immune system. Some immune deficiency diseases arise when one or more of these genes is defective. Genetic immune deficiency leads to frequent bacterial, viral, or fungal infections. It can increase the likelihood of cancer, or diseases like rheumatoid arthritis and the kind of anemia that results from premature destruction of red blood cells. The immune system may be impaired during fetal development, resulting in a congenital immune deficiency disorder, one that is present from birth but not necessarily inherited. There are nearly 100 inherited or congenital immune deficiency diseases collectively called primary immune deficiency diseases, and these disorders develop in 1 in every 10,000 people. Immune deficiency disease can also develop as a result of an illness, traumatic injury, or therapeutic drug that damages the functioning of the immune system. More common than primary immune deficiency, this type of immune deficiency is called secondary immune deficiency disease. Infectious viruses such as German measles, or rubella, measles, Epstein-Barr virus, and human immunodeficiency virus (HIV) can damage the immune system; so can drugs that suppress the immune system, a lack of proper nutrition, and the process of aging. The progress of acquired immune deficiency disease can be reversed if the underlying cause is treatable.