issue 169 - March 1987
What Causes AIDS?
A virus. In France it was first known as LAV (Lymphadenopathy Associated Virus) because of swollen lymph glands in infected individuals. In the US it was dubbed HTLV III (Human T-Cell Lymphotrophic Virus Type III), because it destroys T-cells - used by the body's immune system to combat diseases, To resolve the confusion the internationally-accepted name is now Human Immunodeficiency Virus (HIV).
Viruses are the smallest of all disease-producing organisms - about 1,000 can fit into a red blood cell, and there's enough space for 300 red blood cells on the point of a ballpen. Despite great progress against other infective agents (for example bacteria - which can now be controlled with antibiotics) viral diseases have so far defied science's efforts to find a cure. There is no cure for the common cold or influenza - both caused by viruses. The disease caused by HIV, however - AIDS - is always fatal once it develops. Also, HIV belongs to a recently discovered class of viruses known as retroviruses - which all cause persistent infection: once in the body, HIV is there for life. Another characteristic is that it operates slowly and may lie dormant and undetected for years.
Graph I Rate of spread of the epidemic
Figures are for total number of cases of full-blown AIDS by year and country.
The graphs show that the rate of progression is virtually identical in every country.
How does the virus work?
By inserting itself into human cells. It 'hijacks' their genetic reproductive mechanism to manufacture more viruses, These kill the host cell and then cascade outwards to infect adjacent cells. In turn these are transformed into 'virus factories' and ultimately killed. HIV 'targets' T-cells, the body's main line of defence against all other infections. People with AIDS thus have drastically weakened immune systems (hence the name Acquired Immune Deficiency Syndrome) and are unable to combat common diseases which uninfected individuals fight off without difficulty
How does the virus make people sick?
Because their immune systems are compromised, people with AIDS are prone to opportunistic infections - i.e. killer diseases that become established only because of severe immune deficiency. The most common of the opportunistic infections that people with AIDS suffer are:
Pneumocystis Carinii Pneumonia (PCP)
80 per cent of the world's population are reckoned to have been exposed to PCP, a parasitic protozoon infection of the respiratory tract. Few get sick their immune systems contain the infection and they suffer no symptoms. People with AIDS however, succumb almost immediately, suffering chest pains, dry coughs, shortage of breath, and high fevers. Death results from collapsed lungs and respiratory failure.
A parasite of the gastro-intestinal tract that causes protracted catastrophic diarrhoea (up to 12 litres emitted per day). The patient dies of dehydration and loss of body salts.
Also a parasite, it attacks the lungs, heart and brain. Death results from encephalitis (inflammation of the brain), preceded by confusion and severe head pains.
CMV can affect the gut (where it causes life-threatening diarrhoea), the brain (fatal encephalitis), and the eyes (destruction of the retina and blindness).
Commonly known as 'thrush' - a minor condition for people with intact immune systems. People with AIDS develop it in disfiguring and life-threatening forms. Oral thrush is particularly common. The fungal growth - a thick white paste - advances to block the throat, proceeding from there into the intestinal tract or lungs.
Also a fungal infection, it affects the brain (cryptococcal meningitis - usually fatal), lungs and heart.
But opportunistic infections are not the only causes of death in people with AIDS. One common killer is not an infection at all but a cancer, Kaposi's Sarcoma (KS). It starts as purple or pink flat and painless lesions on the legs and ankles which may rapidly spread to other parts of the body. It becomes life-threatening when it invades the lower intestine, the lungs or the bones (which it cracks, releasing calcium into the bloodstream and causing great pain).
HIV also has a direct effect on the brain because it targets and destroys not only T-cells but also brain cells. The resulting condition, 'AIDS dementia', is caused by a slow withering of cortical tissue leading ultimately to brain death. Early symptoms are memory loss, headaches, disorientation and bizarre personality changes. Simple tasks like dressing or cooking become impossible and double incontinence is common.
Does every infected person become sick?
Too early to say. It was first thought that only 10 per cent developed full-blown AIDS - succumbed to one or more of the opportunistic infections In 1986, however, this estimate was revised upwards to between 30-50 percent1 As time passes it is probable that even more carriers will develop AIDS. Those who escape opportunistic infection also remain at risk from AIDS dementia as a result of the direct action of the virus on brain cells.
Is there a cure?
All the opportunistic infections respond to treatment. But when treatment is withdrawn they recur, usually more severely. In the end they always kill the patient. Scientists therefore, are looking for a drug that will attack the HIV virus itself and the immunosuppression it causes. After five years of research, no such drug has been found. Some substances kill the virus, but the patient remains immunosuppressed and prone to opportunistic infections. When the anti-viral drug is withdrawn - because of its toxic side-effects - the quantity of virus in the bloodstream quickly returns to its original level The best drug available is Borroughs-Wellcome's AZT(Azidothymadine) which blocks viral replication in some but not all people. It does not alleviate immunosuppression and whether it will prevent carriers who have not yet developed AIDS from progressing to the full-blown disease is unknown.
Possibly more promising is the quest for a vaccine. The time-scale for the development of a safe and successful vaccine is five to ten years.
How widespread is the epidemic?
Very (see map). The US had 26,102 cases of full-blown AIDS in September 1986 (76 in 1980), Canada had 638 cases (July 1986), New Zealand 19 cases (July1986), Britain 610 cases (December 1986), Australia 313 (October 1986). Rates in Western Europe vary, being highest in France and W. Germany (respectively 806 and 675 cases in October 1986).2
The rate of spread of the epidemic in any given population is exponential and very similar from one country to another (see comparisons in Graph I). Initially the number of cases doubles every six months. After two or three years, this slows to a doubling time of 10-12 months, which then remains fairly constant. This established epidemiology means that a country with 600 cases today will have more than 500,000 cases in ten years and one million in eleven years And for each case of full-blown AIDS there are at least 100 symptomless but infectious carriers. America's 26,000 cases mean a carrier population of 2.6 million.3
In the Third World, misdiagnosis and inadequate recording make exact figures difficult. Africa is worst affected, with a carrier population estimated between five and ten million. In 1986, eight per cent of pregnant women attending prenatal clinics in Zaire were found to be infected In Kigali, Rwanda, 18 percent of blood donors were HIV-positive. In Lusaka, Zambia, 33 percent of men aged 30 - 35 were infected.4
Graph II Infection and sexual activity
The more sexual partners you have the more likely you are to become infected - as this chart showing rates of HIV positivity in the three groups indicates. In Nairobi from 1980 - 1986 Up most among female prostitutes. Up significantly among sexually active men. Up least among pregnant women.
How is AIDS transmitted?
It is quite difficult to catch. Transmission is only through infected blood or blood products and through sexual contact involving exchange of bodily fluids. Congenital transmission also occurs - both in the uterus and from breast milk. About 50 per cent of infants born to mothers with AIDS develop the disease shortly after birth. Additionally, pregnancy can precipitate full-blown AIDS in previously healthy HIV-positive mothers,
Screening of blood supplies has removed almost all danger of acquiring the virus through blood transfusions in the rich countries of the North, but users of intravenous drugs who share needles remain very much at risk. In the Third World where few countries have yet been able to afford screening, risk of infection by transfusion is high, particularly in Africa. Fourteen per cent of donated blood in Kampala, Uganda, was infected in 1986 and nearly 20 per cent of Rwanda's HIV-positive children were infected by transfusion.5 Sexual intercourse however, is the main carrier of the epidemic in all parts of the world. In the North, homosexuals remain the worst-affected group, although this is changing as more and more heterosexuals become infected. In Africa, heterosexual intercourse has long been established as the primary transmission route - with numbers of men and women infected being almost equal. Sexually active groups, for example, prostitutes and their clients, are much more prone than those with fewer sexual partners, see Graph II. Successful education campaigns aimed at promoting 'safer sex', see article, could radically reduce the transmission rate. For the present, education remains the best 'vaccine' against AIDS
1 US National Academy of Sciences.
2 Panos Institute Dossier No. 1, London, November 1988.
3 US centres for Disease Control, Morbidity & Mortality Report
4 Panos Institute Dossier, op cit.
5 Panos Institute Dossier, op.cit.