Final answer:
AIDS, or Acquired immunodeficiency syndrome, is the severe stage of HIV infection characterized by a low count of CD4+ T cells, making the body vulnerable to opportunistic infections and diseases. AIDS is diagnosed by a CD4 T-cell count under 200 cells/µL or the presence of certain diseases, and without treatment, the life expectancy is drastically reduced.
Step-by-step explanation:
Acquired immunodeficiency syndrome (AIDS) is a condition that represents the most advanced stage of human immunodeficiency virus (HIV) infection. HIV targets and destroys CD4+ T cells, which are pivotal to the human immune system's function. As the virus progresses, these cell counts drop significantly, leading to a state of immunodeficiency wherein the body becomes highly susceptible to a range of opportunistic infections and diseases.
When the CD4 T-cell count falls below 200 cells per microliter of blood, or when certain opportunistic illnesses such as Pneumocystis pneumonia, tuberculosis, or rare cancers like Kaposi's sarcoma manifest, an individual is diagnosed with AIDS. These complications arise due to the weakened immune system and are often the direct cause of death in individuals with AIDS. Without treatment, a person with AIDS typically has a reduced life expectancy.
It is important to understand that AIDS is not a single disease but rather a spectrum of conditions that result from the cumulative damage to the immune system caused by HIV. Over time, untreated HIV infection leads to a critically low level of helper T cells, at which point the affected person's ability to combat various infections and diseases becomes severely compromised.