It's the soft underbelly of human history: the study of disease and how it affects societies. And historians in that field have, for the past 35 years, toiled under the dark shadow of William MacNeill's Plagues and Peoples, a work that juxtaposed human beings (or "macroparasites") against the "microparasites" that prey upon them. MacNeill painted a relentlessly gloomy picture of man's struggle with infectious diseases, concluding that increased social mobility and an ever-expanding population signalled bleak times ahead.
Now, John Aberth has entered the fray with Plagues in World History. He hasn't done so blithely either. Rather, he's taken the only approach guaranteed to gain him a hearing, by putting MacNeill's thesis under direct scrutiny. In doing so, he recounts the vaguely Malthusian determinism of the master, and then quietly dismisses vast swathes of it: "MacNeill had accorded an overmighty role to disease on the stage of history, which now should give way to a more nuanced, complex interplay of other factors." As mild-mannered as it might seem to the uninitiated, this is heady stuff indeed, especially since so much of MacNeill's heavily footnoted pessimism seems vindicated by recent experience. Aberth begs to differ: "I personally am more hopeful, optimistic, sanguine, or however you wish to call it, than probably most other authors about humans' future at the hands of disease."
As its title indicates, Plagues in World History doesn't look to that future - the past is its focus. Aberth, a specialist on the Black Death, which ravaged Europe in the 14th century, looks at six diseases that have devastated societies: plague, smallpox, tuberculosis, cholera, influenza and Aids. In each chapter, Aberth is concerned not only with the aetiology and presentation of the disease in question, but also its sociological impact.
He's very strong on the science of sickness, using three criteria for choosing which diseases to discuss: its spread must be worldwide, it must have sufficient long-term impact (Aids barely makes the cut, and new sicknesses like "swine" or "bird" flu aren't afforded chapters of their own), and it must be fatal for large numbers of people. As Aberth puts it: "There is nothing like the fear of death for eliciting a response from people."
Aberth splits his attention evenly between the two principle types of pathogen. Tuberculosis, Black Death and cholera are bacteriological; influenza, smallpox and Aids are all viral. Readers unclear on the differences between the two will be relieved to find that Aberth is a deft explainer (put simply, bacteria are microscopic creatures that do all the things animals do whereas viruses are organisms that require the processes of other living things in order to do most of the things we associate with living; bacteria can contract viruses, for instance, but not the reverse). There is a further symmetry in the fact that half of these diseases - Black Death, tuberculosis, and smallpox - have more or less been tamed, whereas the other half - cholera, influenza, and Aids - still run rampant.
The book is, then, a grim little treasure-trove of information. We are reminded of the signal victory of medical science over tuberculosis in 1943, when a regimen of antibiotic drugs were developed to defeat the disease. We learn that the bite of a single flea infected with the septicaemic variant of Yersinia pestis, the plague, could inject 25,000 bacteria into a host. The influenza virus is likewise industrious, constantly mutating as it uses the cellular machinery of its host to replicate itself endlessly: "It is estimated that within a single cell an influenza virus can manufacture and then release up to a hundred copies of itself within five or six hours."
Aberth is dutifully thorough in relating such facts, but his real strengths lie in exploring the social dimensions of the diseases he discusses. He's always sensitive to this aspect, and his insights can be fascinating, as when he reminds us, "Since the pustules formed heaviest on the extremities, smallpox was a very visible disease, practically impossible to hide, so that even though the victim was infectious for as long as he or she exhibited its symptoms, it was also abundantly clear who had the disease and thus who should have been avoided."
He makes sure to rehearse for us the ghastly physical devastation produced by Vibrio cholerae, the cholera bacterium ("Cholera was feared in Europe as almost a second Black Death"), but he always links it to accompanying social developments, as in the case of the massive cholera epidemic that erupted when America acquired the Philippines after the 1898 Spanish-American War: "As with the British experience with plague in India, the United States discovered that its heavy-handed attempts to control cholera, such as isolating victims in camps and destroying or disinfecting their houses, were only counterproductive, inspiring Filipinos to flee or conceal victims of the disease, thus prolonging and even spreading the epidemic." The human face of disease is ever-present in these pages, paradoxically making the book at once more inviting and more heart-wrenching.
This dichotomy is at its sharpest in his chapter on Aids, the newcomer in his rogue's gallery and, as he obliquely acknowledges, the most socially explosive: "Of all the deadly infectious diseases that are discussed in this book, acquired immune deficiency syndrome (Aids) is perhaps the most culturally constructed one, whose ever-shifting 'metaphors' relative to each society's attitudes and behaviours are intimately connected with the clinical and biological manifestations of the disease."
He stresses the radical ways in which Aids' status as a retrovirus separates it from smallpox and influenza: the DNA of the latter two replicate faulty RNA until the host cell dies, at which point the copies are released from the cell membrane, whereas HIV reverses the process, its RNA replicating DNA copies of itself, which it then grafts to the host cell almost indistinguishably, allowing it to spin out more viruses. "The advantage for the retrovirus is that the cell can keep functioning and remain alive to serve the replicating needs of its viral guest, rather like a body taken over by some alien avatar or possessing spirit, whereas other viruses would kill off their host once lysis or release of new copies from the cell membrane is complete."
When it comes to the tangled social aspects of this disease, Aberth lacks his usual sure-footedness. He accurately notes that a shift has taken place in the West's perception of Aids since the early 1980s, often being seen now more as a chronic, "manageable" condition than the pandemic killer it remains in most of sub-Saharan Africa. It's a tricky thing to note that without apportioning blame for it. This can produce some fairly awkward lapses in common sense, such as when he scolds the makers of the 1998 movie The Wedding Singer for making "absolutely no mention" of Aids in a film that is otherwise "steeped in 1980s nostalgia".
There are other minor lapses. Aberth, for example, does public health no favours when he subscribes to the apparently indestructible myth that weather has any effect whatsoever on susceptibility to viruses. We're told that "human immune systems are also more likely to be compromised as the body fights off the effects of cold or rain" even though this is self-evident nonsense: there is no human immunological defence triggered by getting wet, and decades of laboratory experimentation on mice have proven that flu behaves "seasonally" even when conditions of temperature and humidity are kept precisely even all year - obviously, there are other factors (known or not) involved.
But such things amount only to authorial quirks when considered against the sweep of Plagues in World History as a whole. Aberth differs from his great predecessor mainly in terms of his optimism - a hard-won optimism retained even in the face of the terrors he relates. As the human population swells to nine billion and then 10 in this new century, any optimism at all will be much appreciated.
Steve Donoghue is managing editor of Open Letters Monthly.