Aids

AIDS - What's new ? By: Eric Quinley E-mail: cvcdoc@hotmail.com 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 or disturb the immune system. Such triggers may be genetically determined proteins in someone's system, or foreign substances from other infecting organisms - such as syphilis, chlamydia, gonorrhea, HTLV-1 (leukemia), herpes, or CMV (cytomegalovirus) - which somehow awaken the HIV virus. The assumption is that once HIV replication gets going, the lymphocyte destruction cripples the entire immune system. Recent British research suggest that some people may have a serum protein that helps them resist HIV while others may have one that makes them genetically more prone to it by facilitating viral penetration of T-helper cells. Perhaps, says one expert, everybody exposed to HIV can become infected, but whether or not the infection progresses to illness depends on multiple immunogenic factors. Some may be lucky enough to have genes that protect them form AIDS! Variable period until those infected develop antibodies: -------------------------------------------------------- While HIV hides within human cells, the body may produce antibodies, but, for reasons not fully understood, they don't neutralise all the viruses. The presence of HIV antibodies thus does not confer immunity to AIDS, nor prevent HIV transmission. Carriers may be able to infect others. The usual time taken to test positive for HIV antibodies after exposure averages from four to six weeks but can take over a year. Most experts agree that within six months all but 10 per cent of HIV-infected people "seroconvert" and have detectable antibodies. While HIV antibody tests can indicate infection, they are not foolproof. The ELISA is a good screening test that gives a few "false positives" and more "false negatives" indicating that someone who is infected has not yet developed identifiable antibodies.) The more specific Western Blot test, done to confirm a positive ELISA, is very accurate. However, absence of antibodies doesn't guarantee freedom form HIV, as someone may be in the "window period" when, although already infected, they do not yet have measurable levels of HIV antibodies. A seropositive result does not mean someone has AIDS; it means (s)he is carrying antibodies, may be infectious and may develop AIDS at some future time. As to how long seropositive persons