1. HIV and AIDS

HIV (Human Immunodeficiency Virus) is a virus that attacks the immune system, specifically the CD4 cells, which help the body fight infections. If untreated, HIV can progress to AIDS (Acquired Immunodeficiency Syndrome), a severe stage where the immune system is significantly weakened, making the body vulnerable to opportunistic infections and certain cancers. HIV is primarily transmitted through unprotected sex, sharing needles, or from mother to child during childbirth or breastfeeding. While there is no cure, treatment with antiretroviral therapy allows many people with HIV to live long, healthy lives.