what are aids and how it causes?

AIDS i.e. Acquired immune deficiency syndrome, is the final stage of HIV disease, which causes severe damage to the immune system. Human immunodeficiency virus (HIV) causes AIDS.

The virus attacks the immune system and leaves the body vulnerable to a variety of life-threatening infections and cancers. Common pathogens that usually do not cause serious disease in people with healthy immune systems can cause fatal illnesses in people with AIDS.

The virus can be spread (transmitted) through sexual contact, through blood transfusions or needle sharing, from infected pregnant mother to child or from a nursing mother to her baby through her breast milk. Blood, semen, vaginal secretions, and breast milk have been shown to transmit this infection to others.