Six hundred and fifty years ago, the Black Death was stalking Europe. It arrived on ships from Asia, carried by fleas that had infected rats on board the ships. Before it burned itself out, the epidemic had killed about a third of the European population.
Today, another plague – AIDS – has ravaged the world. Although it seems very different from the Black Death, there is one eerie similarity. Both the Black Death bacteria, Yersinia pestis, and HIV, the virus that causes AIDS, home in on macrophages, which are scavenger white blood cells of the immune system.
Now, in a provocative report, scientists at the National Cancer Institute in Frederick, Md., say they have found that a genetic mutation that protects against the AIDS virus, by preventing the virus from entering macrophages, emerged in Europe around the time of the Black Death. And, they have found, this AIDS resistance gene is astonishingly common in people whose ancestors lived in areas of Europe that were ravaged by the Black Death.
The HIV resistance gene destroys a protein, called CCR5, that pokes out of the surface of macrophages, the large white blood cells that can engulf and kill viruses and bacteria.
Scientists have discovered that when HIV infects a person, the virus goes straight to the white blood cells and in particular the macrophages, latches onto CCR5 and another protein, CD4, to hoist itself inside.
It lives there for about a decade, throwing off billions of genetic variants. Eventually it makes a variant that can get into another type of white blood cell, the T cells. Then the infected person’s immune system starts to decline, and the terrible symptoms of AIDS appear.
People who inherit two copies of the HIV resistance gene can only be infected with HIV if they happen to come in contact with a virus from someone in the late stages of infection, when the virus can go straight for the T cells, said Dr. Stephen J. O’Brien, who is chief of the Laboratory of Genomic Diversity at the cancer institute.
O’Brien and others have found that 10 percent of Caucasians have a copy of the gene, which slows the progress of HIV infections by several years, and one percent have two copies, which provides nearly complete immunity to HIV.
The HIV resistance gene is most common among British and other northern European people, and declines in frequency further south. Thus, it is present in almost 14 percent of Swedes but appears in only about 5 percent of Italians and is absent in Saudi Arabia. It is absent in Africans, American Indians and Asians. The gene emerged in the Caucasian population long after Caucasians split from Asians, which was about 50,000 to 100,000 years ago, O’Brien said. And so, although the bubonic plague began in Asia, the HIV resistance gene is not there.
By GINA KOLATA
N.Y. Times, May 26, 1998
Since this article first appeared, it has also been discovered that a gene variant called HLA-B*35px, which is associated with fast progression from HIV to AIDS, is common among people of Indian origin. This means that vaccines tested on people of British Isles and Northern European descent may well have no effect on the more than 5 million Indians who are HIV-positive.
Update on AIDS
It is now known that the CCR5-delta32 allele, which confers strong resistance or perhaps even total immunity to the HIV virus, is found in significant frequencies only in populations of European descent.
This natural genetic immunity means that if HIV were to mutate so as to be able to spread through droplet infection, thus potentially exposing everyone in the world, a significant number of us would survive.
Within Europe itself the frequencies are highest in the north, which has led some researchers to think the allele was spread by the Vikings. Others disagree. At any rate, the -Δ35 allele is most common among people of racially Nordic type. The frequencies for different populations within Europe are shown in the chart above, with the darkest-coloured areas having the highest CCR5-Δ32 resistance.
The precise percentages would be higher than in the chart here, because the researchers have tested people living in the different parts of these zones without regard to their race or sub-race. The large-scale presence of non-Europeans in some of these regions would obviously drag down the overall percentages.
If only racially Nordic people were tested, the frequency would obviously be higher. Take England, for example. The research done so far suggests that of the total population of England about 10% to 12% have the -Δ35 allele. However, according to the 2011 census, only 44.9 per cent of Londoners were “white British”. Of the 53 million people living in England in 2011, just under 80% claimed to be “white British” — let’s say about 42 million.
To use the average of the estimated range, if 11% of the total population has the -Δ32 allele, that comes to 5.83 million individuals. These represent nearly 14% of the total “white British” population. However, probably only racially Nordic white Britons are immune.
Early 20th century anthropologists estimated that 80% of the genuine English were Nordic, but differential breeding rates have probably reduced that figure to perhaps 50% by now. 50% of 42 million is 21 million, of which the 5.83 million who are immune equal nearly 28%.
To sum up so far: at least 14 per cent of British-descended people are genetically protected against HIV. The real figure is probably much higher — maybe in the region of 28% for racially Nordic Britons.
These figures aren’t as accurate as they might look on paper, since the 2011 census was based on self-identification. Many people who wouldn’t be regarded as entirely “white” by a geneticist will have chosen to identify with the “white” portion of their mixed ancestry. (But that self-identification won’t give them the -Δ35 allele.)
However, should the HIV virus mutate such that the whole world is exposed to it, somewhere between 14% and 28% of people with pure British ancestry would survive.
It’s important to stress that this applies as much to people in the overseas “white British” diaspora as it does to people living in the U.K. itself.
Take Australia, for example. In 2011 its total population was 22.34 million. Of these, 50.6% claimed to be of English, Scottish or Irish ancestry. (A further 35% claimed “Australian” ancestry, which is too vague to consider here.) 50.6% of 23.34 million is 11.81 million. 14% of that figure is just over 1.65 million. So in a hypothetical AIDS apocalypse, at least 1.65 million “white British” Australians would survive. This is a minimum survival figure, since it doesn’t include Australians of Scandinavian, Dutch, Baltic, German or similar descent — or many (probably most) of the 35% who wrote “Australian” in the census. It also doesn’t take account of the Nordic percentage of the broader white Australian population.
Even so, for perspective, in the year of Federation the total population of Australia was estimated at 3.76 million. Therefore at the very worst AIDS might cull the population to just under half of those alive in 1901. That’s still more than enough to ensure that the island continent remain inhabited and civilised.
A similar calculation could be made for countries such as New Zealand, Canada and the U.S., not to mention the nations of northern Europe. But it’s hardly necessary.
The World Health Organization estimates that about 39 million people have died of AIDS so far, even though in its present form it is hard to catch. If HIV ever mutates into an airborne disease, the resultant deaths will therefore be in their billions.
Yet no matter what happens, enough people of British and related origin will survive an AIDS apocalypse to ensure that “the world’s great age begins anew”.