AIDS - What\'s new ? ------------------- Is the message getting through? We already know enough about AIDS to prevent its spread, but ignorance, complacency, fear and bigotry continue to stop many from taking adequate precautions. We know enough about how the infection is transmitted to protect ourselves from it without resorting to such extremes as mandatory testing, enforced quarantine or total celibacy. But too few people are heeding the AIDS message. Perhaps many simply don\'t like or want to believe what they hear, preferring to think that AIDS "can\'t happen to them." Experts repeatedly remind us that infective agents do not discriminate, but can infect any and everyone. Like other communicable diseases, AIDS can strike anyone. It is not necessarily confined to a few high-risk groups. We must all protect ourselves from this infection and teach our children about it in time to take effective precautions. Given the right measures, no one need get AIDS. The pandemic continues: ----------------------- Many of us have forgotten about the virulence of widespread epidemics, such as the 1917/18 influenza pandemic which killed over 21 million people, including 50,000 Canadians. Having been lulled into false security by modern antibiotics and vaccines about our ability to conquer infections, the Western world was ill prepared to cope with the advent of AIDS in 1981. (Retro- spective studies now put the first reported U.S. case of AIDS as far back as 1968.) The arrival of a new and lethal virus caught us off guard. Research suggests that the agent responsible for AIDS probably dates from the 1950s, with a chance infection of humans by a modified Simian virus found in African green monkeys. Whatever its origins, scientists surmise that the disease spread from Africa to the Caribbean and Europe, then to the U.S. Current estimates are that 1.5 to 2 million Americans are now probably HIV carriers, with higher numbers in Central Africa and parts of the Caribbean. Recapping AIDS - the facts: --------------------------- AIDS is an insidious, often fatal but less contagious disease than measles, chicken pox or hepatitis B. AIDS is thought to be caused primarily by a virus that invades white blood cells (lymphocytes) - especially T4-lymphocytes or T-helper cells - and certain other body cells, including the brain. In 1983 and 1984, French and U.S. researchers independently identified the virus believed to cause AIDS as an unusual type of slow-acting retrovirus now called "human immunodeficiency virus" or HIV. Like other viruses, HIV is basically a tiny package of genes. But being a retrovirus, it has the rare capacity to copy and insert its genes right into a human cell\'s own chromo- somes (DNA). Once inside a human host cell the retrovirus uses its own enzyme, reverse transcriptase, to copy its genetic code into a DNA molecule which is then incorporated into the host\'s DNA. The virus becomes an integral part of the person\'s body, and is subject to control mechanisms by which it can be switched "on" or "off". But the viral DNA may sit hidden and inactive within human cells for years, until some trigger stimulates it to replicate. Thus HIV may not produce illness until its genes are "turned on" five, ten, fifteen or perhaps more years after the initial infection. During the latent period, HIV carriers who harbour the virus without any sign of illness can unknowingly infect others. On average, the dormant virus seems to be triggered into action three to six years after first invading human cells. When switched on, viral replication may speed along, producing new viruses that destroy fresh lymphocytes. As viral replication spreads, the lymphocyte destruction virtually sabotages the entire immune system. In essence, HIV viruses do not kill people, they merely render the immune system defenceless against other "opportunistic: infections, e.g. yeast invasions, toxoplasmosis, cytomegalovirus and Epstein Barr infections, massive herpes infections, special forms of pneumonia (Pneumocystis carinii - the killer in half of all AIDS patients), and otherwise rare malignant tumours (such as Kaposi\'s sarcoma.) Cofactors may play a crucial contributory role: ----------------------------------------------- What prompts the dormant viral genes suddenly to burst into action and start destroying the immune system is one os the central unsolved challenges about AIDS. Some scientists speculate that HIV replication may be set off by cofactors or transactivators that stimulate