Human immunodeficiency virus infection / acquired immunodeficiency syndrome is a disease of the human immune system caused by infection with human immunodeficiency virus. During the initial infection, a person may experience a brief period of influenza-like illness. This is typically followed by a prolonged period without symptoms. As the illness progresses, it interferes more and more with the immune system, making the person much more likely to get infections, including opportunistic infections and tumors that do not usually affect people who have working immune systems.
source:wikipedia\Image by: tonrulkens