AIDS

= acquired immune deficiency syndrome

a syndrome first identified in Los Angeles in 1981; a description of the causative virus – the human immunodeficiency virus (HIV) – was available in 1983. The virus destroys a subgroup of lymphocytes, the helper T-cells (or CD4 lymphocytes), resulting in suppression of the body's immune response (see immunity). AIDS is essentially a sexually transmitted disease, either homosexually or heterosexually. The two other main routes of spread are via infected blood or blood products (current processing of blood for transfusion and for haemophiliacs has virtually eliminated this danger) and by the maternofetal route. The virus may be transmitted from an infected mother to the child in the uterus or it may be acquired from maternal blood during parturition; it may also be transmitted in breast milk.

Acute infection following exposure to the virus results in the production of antibodies (seroconversion), their presence indicating that infection has taken place. However, not all those who seroconvert progress to chronic infection. For those who do enter a chronic stage there may be illness of varying severity, including persistent generalized involvement of the lymph nodes; what is termed AIDS-related complex (ARC), including intermittent fever, weight loss, diarrhoea, fatigue, and night sweats; and AIDS itself, presenting as opportunistic infections (especially pneumonia caused by Pneumocystis jiroveci) and/or tumours, such as Kaposi's sarcoma.

HIV has been isolated from semen, cervical secretions, plasma, cerebrospinal fluid, tears, saliva, urine, and breast milk but the concentration shows wide variations. Moreover HIV is a fragile virus and does not survive well outside the body. It is therefore considered that ordinary social contact with HIV-positive subjects involves no risk of infection. However, high standards of clinical practice are required by all health workers in order to avoid inadvertent infection via blood, blood products, or body fluids from HIV-positive people. Staff who become HIV-positive are expected to declare their status and will be counselled.

Until recently, AIDS has been considered to be universally fatal, although the type and length of illness preceding death varies considerably. The development of antiretroviral drugs, initially used singly but more recently used in dual or triple combinations, may well modify the gloomy outlook. These drugs include the reverse transcriptase inhibitors and the protease inhibitors.