Grim reaper's little helpers

Anyone who has strolled through the corridors of a medical school can tell when a lecture in tropical parasitology has just finished. The halls suddenly fill with white-faced students desperately searching for a breath of fresh air. Robert Desowitz, a professor of tropical medicine at the University of Hawaii, has delivered many such a lecture in his time. Luckily, he knows just how far into the realm of the ghastly his students or his readers are willing to accompany him. In his latest book, he leavens these grim discussions with an engaging sense of humour and a keen eye for the grotesqueries of both the natural world and that of human behaviour.

The book itself is a bit of a potpourri. He examines the impact of both tropical and temperate-zone diseases, ranging from pre-Columbian America to the near future, and in the process picks and chooses among many possible topics. Readers searching for an underlying theme will be disappointed, but there is much to enlighten and entertain them along the way. He is particularly good with the diseases he knows best, giving highly anecdotal histories of yellow fever, malaria and leishmaniasis in the Americas with emphasis on the United States, and occasional glances at the rest of the world. At one point, he gives a fictionalised account of the onset of malaria in a dirt farmer in the US south, so vividly done that it is obvious he is drawing on personal experience with the disease. And he gives full credit to the Rockefeller Foundation in its long fight against yellow fever and hookworm in the US and Mexico during the early part of this century when the civilian US government was doing very little. This is a valuable corrective to those revisionist historians who have tried to portray the foundation as venal and imperialistic.

Diseases can have an enormous impact, both physical and psychological. He examines contemporary accounts of the mortality among native Americans after the Spanish conquest, and concludes that none of the reported diseases, alone or in combination, could have been enough to cause such devastation. When he turns to accounts of the effects of newly introduced diseases on native peoples, he is convinced that the psychological impact of watching their societies and way of life crumble must have contributed to the mortality as well. Elsewhere in the book, he makes a powerful argument that the US would reap a harvest of goodwill were it to set aside a tiny fraction of the resources devoted to hypertension and obesity among its own citizens, and use them to fight some of the great killers of the under-developed world.

But he falls short of making an important connection between these two ideas. The hideous anarchy seen in so much of Central Africa today can be traced in good part to the hopelessness engendered by living in a society wracked by disease. Why work together for tomorrow, when there probably will be no tomorrow? We should realise that a fight against these tropical diseases will have an enormous payoff in social stability as well as goodwill.

It is the duty of the reviewer to pick a few bones, of course. Had his book been a bit better organised, Desowitz surely would have made that powerful connection. And I wonder that he did not make another connection as well. Malaria, so widespread in the south-eastern US down to the 1930s, has now been virtually eradicated, and has not returned in spite of the fact that the use of DDT has now been discontinued. Why? He does not, I think, give enough weight to the fact that we have changed the entire ecological balance of the area, with consequences that we can only dimly foresee. Throughout the book, one kept waiting for him to make this and other important connections that would put all these tropical diseases in perspective.

Another small bone of contention concerns his account of the introduction of syphilis to Europe. He favours the theory that Columbus introduced it, even though Columbus's voyage was only one of many voyages of exploration that were taking place at the time and that were beginning to establish trade routes with sub-Saharan and East Africa and the Far East as well as the Americas. He strays once again into fiction, giving an imaginary account of one of Columbus's sailors who supposedly brought syphilis back from the first voyage. The ultimate source of this rumour, it turns out, is the manuscript version of a book published in 1539 by the Spanish doctor Diaz de Isla. The good doctor claimed in his manuscript to have treated some of Columbus's sailors for syphilis, though this statement disappeared by the time the book was published. But elsewhere in Diaz's book he was utterly confused in his accounts of the origin of the disease, claiming at one point that it came from Hispaniola and at another that it had been known since ancient times. Having waded, with the aid of my daughter, through the book's medieval Spanish, I have come to the conclusion that Diaz de Isla was not what today we would call a linear thinker.

To settle the question, we need to determine the true relationship among the spirochetes that cause syphilis and the closely related diseases of yaws, bejel and pinta, so that they can be distinguished with certainty at the molecular level. We would also love to have clear evidence of the presence of the syphilis spirochete itself from pre-Columbian burials, and thanks to the molecular miracle of PCR this may soon be possible.

These quibbles aside, I enjoyed Desowitz's book very much indeed. At the end of the book, he paints a grim picture of a future in which, because of overpopulation and of global warming and other ecological disturbances, old and new tropical diseases will spread once more. And he makes an impassioned plea for more basic research, not just on how these diseases work, but on cell biology and even on tropical ecology. I could not agree more, and I hope that his words are heeded.

Christopher Wills is professor of biology, University of California, San Diego, United States.