Spillover - By David Quammen Page 0,171

delineated, its initial standing for “outlier,” because it encompassed only a small number of viral isolates, mostly traceable to what seemed an outlier area relative to the hotspots of the pandemic: Gabon, Equatorial Guinea, and Cameroon, all in western Central Africa. By the time a third major group was discovered, in 1998, it seemed logical to label that one N, supposedly indicating “non-M/non-O” but also filling in the alphabetical sequence. (Years later, a fourth group would be identified and labeled P.) Group N was extremely rare; it had been found in just two people from Cameroon. The rarity of N and O put group M dramatically in relief. M was everywhere. Why had that particular lineage of virus, and not the other two (or three), spread so broadly and lethally around the planet?

Parallel research on HIV-2, the less virulent virus, also found distinct groups but even more of them. Their labeling came from the beginning of the alphabet rather than the middle, and by the year 2000 seven groups of HIV-2 were known: A, B, C, D, E, F, and G. (An eighth group, turning up later, became H.) Again, most of them were extremely rare—each represented, in fact, by a viral sample taken from only one person. Groups A and B weren’t rare; they accounted for the majority of HIV-2 cases. Group A was more common than group B, especially in Guinea-Bissau and Europe. Group B was traceable mainly to countries on the eastern end of West Africa, such as Ghana and Côte d’Ivoire. Groups C through H, although tiny in total numbers, were significant in showing a range of diversity.

As the new century began, AIDS researchers pondered this roster of different viral lineages: seven groups of HIV-2 and three groups of HIV-1. The seven groups of HIV-2, distinct as they were from one another, all resembled SIVsm, the virus endemic in sooty mangabeys. (So did the later addition, group H.) The three kinds of HIV-1 all resembled SIVcpz, from chimps. (The eventual fourth kind, group P, is most closely related to SIV from gorillas.) Now here’s the part that, as it percolates into your brain, should cause a shudder: Scientists think that each of those twelve groups (eight of HIV-2, four of HIV-1) reflects an independent instance of cross-species transmission. Twelve spillovers.

In other words, HIV hasn’t happened to humanity just once. It has happened at least a dozen times—a dozen that we know of, and probably many more times in earlier history. Therefore it wasn’t a highly improbable event. It wasn’t a singular piece of vastly unlikely bad luck, striking humankind with devastating results—like a comet come knuckleballing across the infinitude of space to smack planet Earth and extinguish the dinosaurs. No. The arrival of HIV in human bloodstreams was, on the contrary, part of a small trend. Due to the nature of our interactions with African primates, it seems to occur pretty often.

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Which raises a few large questions. If the spillover of SIV into humans has happened at least twelve times, why has the AIDS pandemic happened only once? And why did it happen when it did? Why didn’t it happen decades or centuries earlier? Those questions entangle themselves with three others, more concrete, less speculative, to which I’ve already alluded: When, where, and how did the AIDS pandemic begin?

First let’s consider when. We know from Michael Gottlieb’s evidence that HIV had reached homosexual men in California by late 1980. We know from the case of Grethe Rask that it lurked in Zaire by 1977. We know that Gaëtan Dugas wasn’t really Patient Zero. But if those people and places don’t mark a real beginning point in time, what does? When did the fateful strain of virus, HIV-1 group M, enter the human population?

Two lines of evidence call attention to 1959.

In September of that year, a young print-shop worker in Manchester, England, died of what seemed to be immune-system failure. Because he spent a couple years in the Royal Navy before returning to his hometown and his job, this unfortunate man has been labeled “the Manchester sailor.” His health went into decline after his naval hitch, which he served mainly but not entirely in England. At least once he sailed as far as Gibraltar. Back in Manchester by November 1957, he wasted away, suffering some of the symptoms later associated with AIDS, including weight loss, fevers, a nagging cough, and opportunistic infections, including Pneumocystis jirovecii, but no underlying cause of death could be determined by the doctor

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