AIDS

AIDS is Acquired Immuno Deficiency Syndrome: an immune deficiency acquired during life, so not congenital, and a syndrome, meaning a group of symptoms. It was first reported in 1981 and in about twenty-five years killed more than 25 million people worldwide.

Its cause is HIV, the Human Immuno deficiency Virus, a retrovirus: an RNA genome inside an envelope.

HIV spreads by sexual contact with an infected person, by transfusion of contaminated blood and blood products, by sharing infected needles (intravenous drug abusers) and from an infected mother to her child through the placenta.

HIV is not spread by touch or physical contact, only through body fluids, so infected people should not be isolated from family and society.

Between infection and the appearance of AIDS symptoms lies a time-lag that may be months or many years long, usually 5-10 years.

In the body, HIV enters macrophages. Reverse transcriptase copies its RNA genome into viral DNA, which is incorporated into the host cell's DNA and directs the cell to make virus particles; the macrophage becomes an HIV factory.

HIV also enters helper T-lymphocytes (TH), replicates and releases progeny viruses that attack more helper T cells. Repeated rounds steadily lower the number of helper T cells; meanwhile the person has bouts of fever, diarrhoea and weight loss.

With too few helper T cells, the person falls ill with infections that would otherwise be overcome: bacteria (especially Mycobacterium), viruses, fungi and parasites such as Toxoplasma.

ELISA (enzyme linked immuno-sorbent assay) is a widely used diagnostic test. Anti-retroviral drugs are only partially effective: they prolong life but cannot prevent death.

With no cure available, prevention is what protects people. NACO, NGOs and WHO programmes work for safe blood, disposable needles and syringes only, free condoms, control of drug abuse, safe sex and regular HIV check-ups for susceptible groups; infection should never be hidden.