Acquired Immunodeficiency Syndrome (AIDS)
| Overview |
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- Acquired Immunodeficiency Syndrome (AIDS) is a secondary Immunodeficiency Disease which represents the clinical end-stage of HIV-mediated attrition of Cell-mediated Immunity. Infection with HIV is the root cause of AIDS and the virus slowly but inexorably kills CD4+ T-cells over the course of years. For most patients, following 7-10 years of chronic infection, numbers of peripheral T-cells decline to the point that defects in cell-mediated immunity reach a clinical threshold. The basic pathogenesis of HIV infection can be reviewed on its own page. Here we simply delineate the constellation of clinical consequences which are associated with AIDS. Mild clinical symptoms begin to appear when peripheral T-cells fall below 500cells/uL of blood while severe immunodeficiency manifests when T-cell counts fall below 200cells/uL of blood.
| Clinical Consequences |
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- Overview
- Progression to AIDS is often heralded by infection with a spectrum of organisms which do not normally colonize healthy individuals and are thus termed "Opportunistic Organisms". Although we do not highlight the organisms here, the susceptibility to infection of AIDS patients also extends to more run-of-the-mill microbes to which there is also significantly reduced immunity. In addition, individuals with AIDS display an increased incidence of certain neoplasms along with a unique constellation of CNS impairments.
- Infection Susceptibility
- Respiratory Infections: Pneumocystis, Mycobacterium tuberculosis, Mycobacterium avium Complex, Aspergillus, Candida, Nocardia
- GI Infections: CMV, Cryptosporidium, Salmonella, Shigella, Campylobacter jejuni
- Skin: Severe reactivation of Varicella Zoster Virus and Herpes Simplex Virus which can also disseminate
- CNS: CMV, Toxoplasma gondii, Cryptococcus neoformans
- Eye: CMV Retinitis
- Disseminated Infections with Endemic Mycoses, especially Histoplasma and Coccidioides
- Neoplasms
- The increased neoplastic frequency in AIDS patients is likely multi-factorial. The etiology of many of the neoplasms appears to be due to oncogenic viruses and thus reduced cell-mediated immunity to viruses in AIDS patients likely contributes. However, it should be pointed out that cell-mediated immunity is in general important for tumor immunity, even to neoplasms which do not possess a viral etiology.
- Kaposi Sarcoma: Associated with HHV-8 infection.
- Lymphomas: The incidence of a variety of lymphomas are increased, especially Non-Hodgkin Lymphoma. Some are associated with Epstein-Barr Virus infection.
- Cervical Cancers and Anal Cancer: Associated with Human Papilloma Virus Infection.
- CNS Symptomology
- Neurologic disease in AIDS can be due to direct damage of the HIV virus or due to secondary CNS infection with the microbes detailed above. Some form of neurologic impairment is seen in almost all AIDS patients and the syndrome associated with primary neurological damage by the HIV virus itself if known as "HIV Encephalopathy" or the "AIDS Dementia Complex". Among a constellation of symptoms, the neuropsychiatric syndrome includes aceptic meningitis associated with CSF pleocytosis along with progressive encephalopathy and peripheral neuropathy.