Scientists made a giant leap this year in understanding the HIV virus, which u ncannily changes itself as it invades human bodies, writesLesley Cowling
It’s taken more than a decade of concentrated study by thousands of scientists all over the world to begin to understand how HIV operates. Part of the probl
em is that the virus mutates so fast, and has moved so quickly to establish it self worldwide, that keeping up with it is a formidable task.
It involves the efforts of researchers everywhere to map the spread of the vir us and identify the many forms it has taken. A virus is a living creature that grows, reproduces and fights for survival just like us and all the animals. A
nd listening to scientists who study HIV at Johannesburg’s National Institute of Virology, it is difficult not to picture the virus as a thinking intelligen ce that ca n plan and change to accommodate new challenges – the viral equivalent of Napo leon.
In fact, there is no longer just one HIV, but a set of viruses, like different battalions in one army. Each dominates different parts of the world, some sha
ring territory or overlapping with others.
At last count, there were 10 sub-types of HIV-1, numbered from A to J, says re searcher Helba Bredell, a master’s student working at the National Institute o f Virology. Bredell has been identifying types of HIV that appear in South Afr ica, looking at which population groups or areas carry which virus.
Bredell’s results, like those of similar research projects the world over, wil l go into a database based at Los Alamos National Laboratory in the United Sta tes and published in massive volumes or on a computer database.
The initial results are fascinating in what they reveal about South Africa’s p osition between two worlds: Africa and the West.
Bredell’s results show that two types of HIV dominate in South Africa – one is the virus B, which is prevalent in North America, Europe, Australia and much
of South America; the other is virus C, which is common to Africa.
“B was the virus that appeared here first, and was thought to be contracted by local air stewards in New York,” says Dr Lynn Morris of the Institute’s AIDS
Virus Research Unit. Virus B was then associated with homosexual transmission, and still is.
C, on the other hand, is the African form of the virus that is transmitted thr ough heterosexual contact and has rapidly surpassed B as the dominant virus in this area.
What is interesting about the two viruses, she says, is that they are still as sociated with patterns of transmission rather than with particular ethnic grou ps. This means that people who were infected with HIV through homosexual conta ct will, in most cases, have virus B and those infected through heterosexual c ontact will have virus C.
Bredell and Morris say this is probably because C has mutated to make it easie r to infect vaginal cells.
If you imagine the virus as a round sac of viral matter contained in an “envel ope”, then it is the outside “envelope” that mutates to make the different sub types. The matter inside the sac remains the same for most viruses.
The outside envelope is what the body first “sees”; and if it recognises what it sees as an enemy, it will move to neutralise it immediately. It is for this reason that HIV changes its outer form so often – to make it effective in eva
ding the body’s “soldiers”.
It also changes so that it can find the best way to infect the cells that it c onfronts.
The more effective the mutation, the more likely it is that the new subtype wi ll begin to dominate in a region. Morris cites the example of Thailand, where two strains of HIV were found a few years ago.
One was subtype E, found among intravenous drug users, the other the more wide spread B, found in sex workers. A few years later, however, subtype B began to dominate in both groups, overtaking and more-or-less replacing E.
Apart from B and C, South African researchers have also found a few people inf ected with the subtype D. It comes from East Africa and, like B, is associated with homosexual transmission. But most of the people with the D subtype were
immigrants or visitors from those areas.
The mapping of different viruses worldwide is part of the study of HIV epidemi ology, which seeks to discover how the virus was transferred from one region t o another, where it came from and what kinds of medical strategies should be a pplied in different countries.
It is clear from South Africa’s results so far that HIV entered the country fr om America via homosexual transmission and from Africa via heterosexual transm ission. What is still not clear to researchers, however, is where the virus ca me from, although most signs point to Central Africa.
Most subtypes of HIV-1 are found in that region, as well as a very different f orm called O, and a related virus called HIV-2. It seems that the virus must h ave originated there if there are so many mutations present.
Another reason for mapping the virus is to gather information that might be im portant in designing a vaccine.
“We first need to identify the enemy before we make bullets,” says Bredell.
Although drug treatment of HIV took a giant leap forward this year, the work o n developing a vaccine was slow and on a much smaller scale. The idea of a vac cine is that it would help the body to recognise and neutralise invading HIV c ells by stimulating the immune system before the person is exposed to the viru s.
But if HIV can change its outer envelope (the face it shows the body’s cells), there are great difficulties in designing a vaccine that can help the body re
cognise all the different subtypes.
However, there are people who seem not to be infected by HIV, even though they may have been exposed to it many times. This implies that they have a natural
immunity.
If the secrets of that immunity can be found, scientists may eventually find a way to pass that on to the rest of us. When that day comes, HIV will go the w
ay of polio, smallpox and whooping cough – into the history books.