HIV is a virus, while AIDS is a condition or syndrome that develops in patients who have HIV, explains the San Francisco AIDS Foundation. Patients can have HIV without developing AIDS, but everyone with AIDS already has HIV.
Exposure to HIV can lead to an infection that attacks the immune system, according to Healthline. AIDS develops in a patient with a case of HIV that has severely damaged his immune system. Symptoms of AIDS vary among patients, but common examples include pneumonia, tuberculosis, specific types of cancer and other related infections. As of 2015, there is no cure for HIV, and the immune system is unable to fight and completely rid the body of the infection, even if the patient never develops AIDS.
HIV is contracted when a person exchanges bodily fluids with an infected person, explains Healthline. The virus is most commonly transmitted via contaminated needles or unprotected sex. The virus also can be inherited from a mother during pregnancy or transmitted through a blood transfusion. Taking a saliva or blood test that looks for antigens or antibodies that the body produces to fight the virus can determine if a person has been infected with HIV. Diagnosing AIDS requires counting the body's CD4 cells and looking for opportunistic infections.