Friday, November 04, 2005

Beyond the fringe

Those of you following the little nuclear exchange over at the Scientific American blog between its blogger, John Rennie, Wendy Orent, Paul Ewald and Revere may wish to check in on my rather acerbic response to Ewald there.

I appreciated the opportunity Rennie gave me to respond. I have a minor complaint at his calling "foul" over my characterization of Ewald as a fringe figure. I have emailed him a response on that point, and here it is:

Thank you for posting my reply to Paul Ewald. I would like to draw your attention to an exchange of letters in The New Republic between Marc Lipsitch/Carl Bergstrom and Wendy Orent on the same subject, Paul Ewald's scientific theories. For the record, I am neither Marc nor his co-author Carl Bergstrom. I know Marc (but he doesn't know me as Revere) since we both do mathematical modeling. I don't know Carl. Lipsitch and Bergstrom refer to Ewald's work as based on fringe scientific arguments, which I acknowledge does not make him a fringe figure. On the other hand, his claim that so many diseases are actually microbial in origin, does make him a fringe figure. Few accept this. It doesn't make him wrong. It makes him a fringe figure, for which his own manner has much to blame. He makes sweeping, immodest claims which also accuse everyone else of being wrong.

Consider this blurb for Ewalds's book, Plague Time:
So what will the decisive medical technologies of the future be, if it is indeed accepted that many chronic illnesses are caused by infection? The author believes that, "Vaccines, antimicrobials, and hygienic improvements may control most heart disease, infertility, mental illnesses, and cancers, especially if these solutions are used not just to decimate pathogens but also to direct the evolution of the causative microbes."
I am an environmental epidemiologist, so I'm sympathetic to the general thesis that improvements in the environment are superior public health practice to individually directed medical care. I doubt, however, that the sweeping thesis that Ewald trumpets will be sustained, but even if it is at some time in the future, it certainly qualifies at this point to being on the fringe. The far fringe.

So let me cry "foul" back.


Here is the exchange of letters in The New Republic:
First Lipsitch and Bergstrom:

Wendy Orent suggests we needn't worry about the next influenza pandemic, but her argument is no more than a dangerous case of hope mixed with ideology, masquerading as scientific fact ("Chicken Little," September 12). Flu pandemics occur every few decades. It has been 37 years since the last pandemic, and the h5n1 bird flu virus has an unprecedented combination of traits that make it a prime candidate for causing the next one: It is broadly dispersed across Asia, it is highly pathogenic in humans and some birds, and it is highly prevalent in birds. No responsible scientist has predicted with certainty that the next pandemic will be as bad as 1918, when Philadelphia faced coffin shortages and San Francisco suspended garbage pickup because 80 percent of its sanitary workers failed to show up for work.

But Orent is irresponsible to claim that the "new field called evolutionary epidemiology" is "proving" that another severe pandemic is impossible. This claim is based on a set of fringe scientific arguments that have been extensively tested--and largely refuted--over the past decade. [my emphasis] A recent scientific review of the relevant studies from Trends in Microbiology concluded that there is "little theoretical justification and no empirical evidence" for the ideas Orent and her source, Dr. Paul W. Ewald, use in attributing the severity of the 1918 pandemic to the trench-warfare conditions of the Western Front. The argument also goes against common sense. The SARS virus, which was more deadly to infected people than even the 1918 flu, emerged without trench warfare. Indeed, it appeared in conditions similar to those in which it is feared the next pandemic flu strain might arise.

SARS in Toronto showed us how a new and feared disease can put a whole city into economic and social crisis for several months, even by striking only a few hundred people. Dramatic as its effects were, however, sars is easy to control, relative to pandemic flu. SARS patients can be diagnosed days before they are likely to infect others, making isolation and quarantine measures possible and ultimately successful. With flu, a person can infect others within a day of becoming infected, even before his own symptoms appear. Unlike sars, pandemic flu will spread uncontrolled unless we have vaccine supplies dramatically larger than what we have now or those our health officials are contemplating. Counting on the alleged certainties of one scientist's unproven hypotheses to shield us from another severe flu pandemic is the height of faith-based policymaking. Hoping for the best, and planning accordingly, proved disastrous in New Orleans. We must do better in preparing for the next flu pandemic.

Marc Lipsitch Carl T. Bergstrom The authors are, respectively, an associate professor of epidemiology at the Harvard School of Public Health and an assistant professor of biology at the University of Washington.

Wendy Orent responds:

Marc Lipsitch and Carl T. Bergstrom accuse me of peddling ideology in the guise of science. But there's little accurate science in their letter. First, they assert that flu pandemics occur every few decades. This is meaningless. The only three pandemics we can identify for certain are those of the twentieth century: 1918, 1957, 1968--hardly "every few decades." The idea of being overdue for a new pandemic led to the mass vaccination of over 40 million people during the swine flu scare of 1976. There was no pandemic, but at least 25 people died from the vaccine. Thirty-seven years after the pandemic of 1968, Dr. Edwin Kilbourne, who argued for periodicity and led the drive for swine flu vaccination, insists that the idea of periodicity is dead. There is now no logical reason to believe in it.

Lipsitch and Bergstrom claim that "an unprecedented combination of traits" make h5n1 a "prime candidate" for the next pandemic. But, as usda poultry-flu expert David Swayne points out, no known pandemic has been caused by highly pathogenic avian flu. Over the past two years, h5n1 has spread in birds across Asia; why have only 62 people died of bird flu? Why haven't there been, at most, more than a few instances of probable person-to-person transmission? Why is there such a low rate of subclinical infection among health workers caring for h5n1 patients--unlike sars, where most cases spread in hospitals? Lipsitch and Bergstrom do not say.

The writers attack Ewald's explanation for the exceptional virulence of the 1918 flu as a "fringe" argument. They cite a 2003 article that says there is "little theoretical justification and no empirical evidence" for Ewald's argument. But its authors get that argument wrong. Ewald uses Darwinian logic to argue that the Western Front allowed the repeated infection of new hosts by people immobilized by illness. The precise conditions of the Front, the hospitals, trucks, trains, and trenches packed deathly ill soldiers shoulder to shoulder with the well. Normal flu depends on host mobility: It can't knock its host down, or it won't spread. But, in the trenches, those brakes to virulence were off, and lethal flu evolved. The study's authors think Ewald is talking about ordinary crowding: They announce that Ewald is wrong and crowding won't boost flu virulence. Of course it won't. That was never Ewald's argument--though Lipsitch and Bergstrom appear not to realize that.
Elevated from the Comments (by an anonymous commenter): Paul Ewald a "fringe" figure? You don't say. Not the same Paul Ewald who speculated that homosexuality is an infectious disease in the 1999 Atlantic Monthly article (Feb 1999. Vol.283, Iss. 2, p. 41-51)?
This leads to a subject that Ewald is not shy about bringing up in discussions with colleagues and in professional lectures: homosexuality. Various pieces of evidence have been adduced in recent years, by prominent researchers, for some sort of genetic component to homosexuality. The question arises as to whether natural selection would sustain a homosexual trait in the gene pool for any length of time. The best estimates of the fitness cost of homosexuality hover around 80 percent: in other words, gay men (in modern times, at least) have only 20 percent as many offspring as heterosexuals have. Simple math shows how quickly an evolutionarily disadvantageous trait like this should dwindle, if it is a simple genetic phenomenon. The researchers Richard Pillard, at the Boston University School of Medicine, and Dean Hamer, at the National Cancer Institute, are not persuaded that natural selection would necessarily have eliminated a homosexual trait, and offer ingenious counterarguments. (And they note that historically the fitness cost may not have been very high, when gay men stayed in the closet, married, and had children.)

No one, of course, has ever isolated a bacterium or a virus responsible for sexual orientation, and speculations about the manner in which such an agent would be transmitted can be nothing more than that. But Ewald and Cochran contend that the severe "fitness hit" of homosexuality is a red flag that should not be ignored, and that an infectious process should at least be explored. "It's a very sensitive subject," Ewald admits, "and I don't want to be accused of gay-bashing. But I think the idea is viable. What scientists are supposed to do is evaluate an idea on the soundness of the logic and the testing of the predictions it can generate."

Judith Hooper. (1999) A new germ theory. The Atlantic Monthly. Boston: Feb 1999. Vol.283, Iss. 2, p. 41-51.
My addendum to the Comment: Ewald is entitled to speculation consistent with his overall theory. He is careful to say his is a value-free judgment (and I take him at his word, here; if you believe his thesis you are led to something like this). But it is entirely appropriate to say that speculating that same sex orientation is a microbial condition (I won't say disease here out of fairness to Ewald) is a fringe view.