Using genome analysis, molecular biologists trace the epidemic’s path
What does the molecular epidemiology of AIDS have to offer? By analyzing the genome, we can find the virus’s «fingerprints» and understand how it has spread around the world. For example, if we find a fingerprint of the virus from Thailand in Greece, it means there has been some communication and transmission. But it’s not just the epidemiology that’s interesting. During the study, we saw that in many countries there are completely different cells, nine HIV subtypes altogether. This classification may be of great interest for diagnostic tests, which were originally made for subtype B, and have often failed with other subtypes. That problem has now been partially resolved, but we can’t say the same for drug treatment. We have evidence that some HIV subtypes respond less to drugs, but that question remains open. The third and most serious problem concerns vaccines. There are strong indications that the vaccines will work on only one subtype. So we have to know which HIV viruses there are in each region. In South Africa, vaccines used in research are for subtype C, while in the West (the USA and most European countries), Japan and Thailand, they are for subtype B. Many studies have been conducted in Greece on the genetic heterogeneity of HIV, by the National Retrovirus Reference Center, for instance. How many subtypes were found? The European subtype B (80 percent), A (12 percent), C (2 percent), D (1 percent), G (0.3 percent), F (0.3 percent) and H (0.3 percent). A high proportion (5 percent) of recombinant HIV strains coexist. Someone in a high-risk category, for example a prostitute or an intravenous narcotics user who often shares needles, may be simultaneously infected by one, two or three types together. These strains recombine within the body and the «best,» the most adaptable, dominates and starts to be transmitted. Some of these recombinant strains are connected with greater transmission. Can such a strain «escape» through blood donation? Luckily it cannot. It can’t beat the antibody test. There was a problem with the molecular diagnostic tests, where we measured the viral load and the resistance developed by the virus to drug treatment. But they have improved and we don’t have particular problems with the usual viral subtypes. However the picture may change with the recombinant strains and that demands vigilance. It is obvious that in a few years, as the virus changes, diagnostic tests must change too. Does this happen only in Greece? The Greek picture looks a bit like that of France, Switzerland and Britain, but it is completely different from that of the rest of the West, such as the USA, Spain and Italy. Greece differs from the countries where the virus was spread rapidly via intravenous drug use or homosexual activity. In Greece and Britain the infection was introduced to a great extent by heterosexuals, resulting in a multiplicity of viruses, and the problem gets worse with time. On the world map we can see that most subtypes and most recombinant strains are to be found in Africa, where the infection is very common and an individual might be infected by two or three subtypes. In North Africa, subtype B happened to be introduced and it spread rapidly among the homosexual population. The same occurred with homosexuals and drug addicts in Europe. Heterosexual transmissions mainly started in Africa, where all the subtypes exist. The first Greeks to contract the virus are known to have traveled frequently to African countries. Can molecular biology help us study the history of how AIDS spread? The history and what we call the archaeology of HIV. By studying the genome of the recombinant strains, we see parts of the genome that do not belong to any subtype that has been described so far. This means they are parts of some virus that were entire at the beginning of this epidemic, and were then not passed on completely, with the result that they vanished or became extremely rare. We suppose that these old subtypes come from the initial strains that were transmitted by a chimpanzee to a human. In Greece, apart from type I we have another unique recombinant form comprised of sequences from subtypes A, G, J, K and another part of an unknown subtype which has presumably become extinct. How did AIDS spread? The main route was migration and travel. We know that the rare Virus I mentioned before was brought to Greece by an African economic migrant. The earliest known case of infection by the «Greek» subtype I was a Greek who was very active sexually and who traveled a lot. He infected a large number of women and they passed it on to their partners and children, creating an epidemic of 35 cases in northern Greece which has been described by epidemiologist V. Kioses. This virus does not exist in Africa and it may be extremely rare, or those who had it may have died. But the clone exists in Greece. The epidemic was spread in southern China and Russia by intravenous drug users, and it was introduced to the Caribbean largely by Cuban soldiers who had spent many years in Africa. And of course there is sex tourism, through which an interlinked HIV subtype from Thailand, the old E subtype, got established in Europe. In Greece, a lot of the non-B subtypes have come from sailors, who were one of the first groups to transmit the virus.
