Philip Alcabes discusses myths of health, disease and risk.

Plague Did Not Begin in China. And Why Should Anyone Think It Did?

Nicholas Wade, the NY Times‘s science writer, jumps the gun with a story today asserting that plague began in China.  Maybe it’s understandable:  you don’t often get a front-page story if you’re a science reporter, so once in a while you take some shaky science and turn it into an international incident.

But to understand why the story is wrong means recognizing a weakness of science as it’s often practiced today.

Wade’s claim is based on two papers published this month.  A relatively well done study by Haensch et al. in PLoS Pathogens earlier in October tested human remains from well-identified plague pits — burial sites for medieval plague victims — in different parts of Europe.  Researchers amplified DNA sequences of the plague bacterium, Yersinia pestis, at specific genetic loci, and tested to see whether the DNA matched known sequences of contemporary Y. pestis genes.

The findings published in PLoS suggest that the Black Death and perhaps subsequent waves of plague in Europe were indeed caused by Y. pestis — which would tend to debunk the theory proposed by some British researchers that the Black Death was some kind of viral hemorrhagic fever outbreak.  And they suggest that there were at least two widely different Y. pestis strains involved in different parts of Europe.  Here’s a bit of the abstract:

[O]n the basis of 17 single nucleotide polymorphisms plus the absence of a deletion in glpD gene, our aDNA results identified two previously unknown but related clades of Y. pestis associated with distinct medieval mass graves. These findings suggest that plague was imported to Europe on two or more occasions, each following a distinct route.

The main weakness here is that DNA could not be amplified from all of the plague pits the researchers studied, but after using alternative means to test the DNA debris against contemporary gene sequences the investigators concluded that the absence of genetic material reminiscent of one strain of Y. pestis was evidence that that strain was not in play in that part of Europe at the time.  Probably right, but stretching the available evidence.

It’s a common mistake, alas.  To paraphrase Karl Popper:  just because you see DNA from white swans and don’t see any DNA from black swans, doesn’t mean that black swans don’t exist.

Still, the PLoS paper is persuasive that more than one strain of the plague bacterium was circulating, and probably causing deaths, in the plague period in Europe.  Of course, it says nothing about China.

So where does the NYT reporter get his headline-grabbing story?  A paper to be published in Nature Genetics online (still embargoed at the time I’m writing, but a summary appears here) states that the sequences of plague DNA amplified from plague pit remains, as well as contemporary isolates, can be placed on a molecular clock because of the occurrence of unique mutations.  Winding the clock backward, the researchers conclude that the Ur plague organism, ancestor of all Y. pestis, came from the far east.

The molecular biology may be unimpeachable, but the inferences about history aren’t supportable by molecular evidence.  That might explain why they’re almost certainly wrong.

The problem (scientists, I hope you’re listening!) is that you may know very well what you know, but you can never know what you haven’t seen.  The hereditary tree has its roots in China.  Here is one proposed by some of the same authors in a 2004 PNAS paper:

In this set-up, isolates of Y. pestis from China seem closest to the primordial strains.

But of course, the molecular clock doesn’t take account of strains that are no longer extant.  And ones that haven’t been unearthed.  The contemporary researchers don’t see them (or don’t know how to look), so they don’t exist.

It’s a bad mistake, inferentially.  And historically.  It’s where the NYT writer goes wrong.  Almost certainly, plague did not begin in China.  It began as an enzootic infection of small mammals in the uplands of central Asia.  This is the story convincingly relayed by William H. McNeill in Plagues and Peoples a generation ago, and none of the many accounts I’ve read since then has debunked it.

Plague would have had to begin in an ecosystem in which it could circulate at moderate transmission rates with little pathogenicity among small mammals (the natural host of the bacterium).  Exactly where it started remains open to question, but it was probably in the area that is now Turkestan/Uzbekistan.  With the development of trade between that region and China, intermixing of local (central-Asian) animals with caravan-accompanying rats would have allowed Y. pestis to adapt to the latter.

Quite possibly China was the source of the first human outbreaks of plague — because the river valleys of China were settled and agricultural (therefore offering feeding opportunities for rats as well as multiple opportunities for rat-human interaction) long before Europe was.  That fact probably accounts for the biologists’ (mistaken) belief that their early samples show that Y. pestis started out in China.

But plague began as — and remains — a disease of animals.  To acknowledge that human outbreaks in China preceded the human outbreaks in Europe (the Justinian plague that began in the mid-sixth century, the Black Death that began in the 1340s, and subsequent visitations) is not the same as saying that plague originated in China.

Which it didn’t.  Plague is an animal disease from Central Asia.  Plague’s long history is the usual one:  ecosystem change, trade, animal-human interactions, alterations in climate and economic conditions, and occasional opportunities for mass human illness.   (One world, one health.)

Above all, remember that science is only capable of drawing conclusions about what scientists can observe.  Don’t be taken in by hair-raising stories.  Even in the NY Times.

By Philip Alcabes | October 31st, 2010 | Categories: climate change, Disease, epidemics, Narratives, science, Uncategorized | Tags: , , , | 3 comments

Bed Bug Worry, Mosquito Mayhem

You hear a lot about bed bugs these days, here in New York City.   The bed bug infestation has become part of New York angst, the newest of our plagues.  The NY Times had its top infectious disease writer cover the recent CDC-EPA joint statement on bed bug control.  There’s even an iPhone app with GPS-enabled bed bug maps of New York and other big cities.

Early this month, a couple of friends, thinking they might splurge on a downtown hotel to celebrate their tenth wedding anniversary, were soliciting bed bug reports before choosing where to stay.  And at a family gathering last week, one young man — recently graduated from an elite college, an intellectual usually given to ironic mockery of the nuttier trends evident in the generation that still uses e-mail — told me that while he’s afraid of bees and doesn’t like mosquitoes, bed bugs really terrify him.

Bed bugs are unpleasant.  Their bites can itch.  Their feces and molted shells can set off asthma attacks or other allergies.  It’s sensible to avoid them, and get rid of them if they’re in your home.  I wrote a few months ago that it makes perfect sense that health authorities do something to limit bed bug woes.

But if you ask me what insects worry me most as a public health professional, I certainly wouldn’t say “bed bugs.”  Ticks, especially as Lyme disease spreads geographically.  Phlebotomine (sand) flies, as leishmaniasis becomes a more serious problem.  Mosquitoes, always.   Bed bugs are far from the top of my list.

The Aedes mosquitoes that carry yellow fever, dengue, rift valley fever, and chikungunya viruses, are most troubling right now.  Ae. aegyptii most of all, of course, but increasingly Ae. albopictus.

An extensive outbreak of rift valley fever in South Africa produced dozens of human cases earlier this year, and seems to be continuing among livestock.  An epidemiologist friend in Europe told me a few weeks back that he and other European disease control specialists, already concerned about dengue and yellow fever, are looking at RVF exposures in the southern part of the continent — a worrisome finding for a virus that has primarily been African.   The European Center for Disease Control is, appropriately, concerned about the establishment of Ae. albopictus in Europe.

Ditto chikungunya, which as produced 33 cases in Delhi, India, this year, possibly including an illness in the city’s mayor.

Dengue  demands control most pressingly of all.  Although the CDC is busily advising Americans not to worry (“Nearly all dengue cases reported in the 48 continental states were acquired elsewhere by travelers or immigrants,” its info page reads), there is active spread through much of the Caribbean basin — see the map at Dengue Watch, for instance.  The Mexican ministry of health reports dengue transmission in areas bordering the U.S.  There has already been an outbreak in Texas (in 2005).  And other highly industrialized countries with strong surveillance and control systems are experiencing dengue cases, including the first report of domestic transmission within France this summer.

(Hats off to Crof at H5N1, who has been following both chikungunya and dengue assiduously.)

The expansion of the range of Ae. albopictus, a secondary but by no means ignorable vector for dengue, makes the geographic extension of these pathogens worthy of concern.

With climate changing, trade routes always in flux, area spraying of insecticide disfavored because of environmental considerations, and of course mosquitoes evolving to take advantage of new niches, it seems unlikely that North Americans can go on counting on the mere improbability that virus and vector will coincide.

Mosquito control programs are in place, and U.S. authorities expend considerable effort at controlling Ae. aegyptii in Puerto Rico.  But the West Nile fever outbreak of 1999 and its subsequent extension in North America reveals the porousness of mosquito control.

Mosquitoes are much more worrisome than bed bugs.

By Philip Alcabes | October 31st, 2010 | Categories: climate change, Disease, epidemics, Outbreaks, public health, Uncategorized | Tags: , , , , , , | Comments Off

A Blog Worth Following

If you haven’t already, put Crawford Kilian’s H5N1 blog on your regular reading list.  There, while you’ll still get updates on the H5N1 avian flu virus and occasional pieces on H1N1 flu (and you can see a multitude of archived posts from 2009  filled with international material on the progress of last year’s flu — and the reaction to it), you now get a much-expanded scope, including news and commentary on the spread of infectious diseases of different sorts.

What I value about H5N1 is the tracking of the mosquito-borne viral diseases, like dengue and chikungunya as well as H1N1, that reveal the effects of the elision of ecosystem boundaries; the close attention to outbreaks that stem from changes in human-animal interactions — like the recent outbreak of plague in Tibet and, of course, H5N1; and the watch it keeps on the vaccine trade, as in yesterday’s post picking up a report in The Nation on the purchase of flu vaccine from France and one last week on a US tech company’s trials of a new flu vaccine (which won’t help the public but is, apparently, already helping the company to get richer).

The kind of close attention to the details of complex interactions amongst humans, animals, and both the natural environment and the economic one that H5N1 shows is indispensable.   It should spur more interest in wresting public health away from the simple-minded mass-vaccination schemes of medical officials in the U.S. and other wealthy countries — the point of which is usually to transfer public monies into the hands of pharmaceutical companies.  And move us to toward a more complex and inclusive view of the nature of health.

By Philip Alcabes | September 28th, 2010 | Categories: climate change, Disease, epidemics, Health Professions, News, Outbreaks, Physicians, public health | Tags: , , , , , , , , | Comments Off

Public Health Priorities: Follow the Money

Thanks to Crof at H5N1 for bringing to our attention a strong editorial in yesterday’s Bangkok Post.   The editorialists note that H1N1 preparedness efforts were not always successful and that WHO, fresh from announcing that the H1N1 pandemic is over, is now promoting fears of renewed outbreaks of H5N1 (avian) flu.  The editorial continues:

While it would be foolish to dismiss such warnings as this latest one on bird flu, it is important we keep a sense of proportion and not let them distract us from countering the unfashionable but widespread potential killers such as tuberculosis, HIV/Aids, diabetes, cancer, dengue and malaria. These are the diseases already causing widespread illness and economic harm….

Rather than competing for cash, the threat from newer diseases should serve as a catalyst to combat existing epidemics.

Competing for cash is key.

Funding for TB languishes, dengue incidence expands, more people with the AIDS virus are getting treated but new infections continue to occur, water scarcity (and displacement because of wars and natural disasters) makes diarrheal illness a persistent problem, and malaria transmission continues to threaten billions of people who live in tropical and subtropical regions — but flu preparedness dominates the public health scene.   Why?

Here’s the infernal logic of WHO and the public health officers of wealthy countries (U.S., U.K., etc.):  (a) At the start of the H1N1 outbreak in 2009, a sensible worst-cast forecast was about a million deaths worldwide; the more likely scenario was well under 500,000 deaths.  (b) TB + malaria + diarrhea + AIDS together kill 6 or 7 million people a year.   (c) Immunization against flu is notoriously variable in its effectiveness and mass immunization is almost never effective (except if instituted in an isolated population well before the flu virus makes inroads into the population).

Sounds like it would be worth it to pump lots of resources into reducing the incidence of malaria, TB, AIDS, and diarrhea.  But that’s hard.  It takes political will.  Whereas immunizing against flu is easy: it just takes money.  And national health officials were eager (it turned out) to transfer billions of dollars, pounds, and euros into the hands of vaccine manufacturers in order to be able to immunize their populations against H1N1 flu.

To an official whose job is to watch out for the needs of the economic machine, immunization pays.

One flu vaccine manufacturer estimates that in the U.S., employers lose $2.1 billion each year in productivity because of flu-related absences from work.  Let’s be skeptical about this estimate, coming as it does from one of the beneficiaries of federal largesse in response to flu fears.  But the point is clear enough:  it was a great boon to the private sector to have the federal government spend $1.6 billion of taxpayer money on flu vaccine in 2009 even though the outbreak was mild and vaccine did virtually nothing to stop it.  Because with the feds footing the bill, the burden on corporations was slight, whereas the private sector would have lost a lot of money if many Americans had fallen ill with flu.

It’s not just the vaccine manufacturers and pharmaceutical companies who stand to capitalize on the absurd calculus of protecting American businesses instead of poor people’s lives:  scientists do, too.

Robert Webster is an eminent virologist who has become dean of those American scientists who purport to be able to foresee a future flu catastrophe.  Perhaps he’s right, but of course nobody knows.  So when Webster says

We may think we can relax and influenza is no longer a problem. I want to assure you that that is not the case,

as he just did in a meeting in Hong Kong, it’s a good sign that the preparedness crusaders are worried about their funding.  They should be.

The preparedness crusaders have been unmasked as shameless shills for the private sector,  even if the vaccine and antiviral manufacturers aren’t paying them directly.  And the ones who are scientists have been revealed as self-important promoters of their own research — so fiercely protective of their own turf that they might use their prestige and the imprimatur of science to hoodwink officials into ignoring the more serious, and more certain, problems of the developing world.

Let’s hope that more opinion makers take the stand that the editors in Bangkok just did.

By Philip Alcabes | September 5th, 2010 | Categories: Disease, epidemics, Outbreaks, public health, Uncategorized | Tags: , , , , , | Comments Off

Media Culture: Beyond Fat and Salt?

Over at Media, Culture & Health, Steven Gorelick notes that a story on salt and the food industry, which appeared on page A1 of the print NY Times on Sunday, would not have made the front page in the past.

What has changed?  How does the story of wrangling over the sodium content of American food merit space in the main news sections of the most influential media — even the front pages of the NY Times or LA Times?

1.  One answer is that health occupies much of the American conversation today.  A visitor from another planet watching our TV news shows or reading the main newspapers would have to be forgiven for thinking that Americans are dying from a multitude of irrepressible disease threats.  We can’t seem to stop talking about how to improve our health.

(In fact, as Michael Haines notes at the Economic History Association website, U.S. life expectancy almost doubled between 1850 and 1960, from 39.5 years to 70.7 years; since then it has increased slowly, and is now estimated to be about 78.2 years.  In other words, health wasn’t a matter of news much during the time when longevity was improving dramatically, in the late 19th century and first half of the 20th.  By the time health became a cultural preoccupation, the majority of Americans were living well past middle age.)

2.  Another answer, perhaps more important is that when we talk about health today we mean personal responsibility.

When I began studying epidemiology, in the late 1970s, public health essentially meant disease control.  Yes, lip service was paid to so-called health promotion — much was made of the World Health Organization’s definition of health, promulgated in 1946:

Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

But no metric for complete well-being was widely recognized.  And the usual epidemiologic measures of incidence and mortality rates, life expectancy, and so forth seemed to work just fine as ways of understanding why some groups of people lived longer and more capable lives, while others lived miserably and died young.

Sometime since then, the health sector, including public health, has turned to individual responsibility as the key to well-being.

If each of us is responsible for his or her own health, then it’s our own fault if we get sick.  Naturally, advice abounds:  buckle up, use a condom, eat less fat, know your cholesterol level, wash your hands, use mosquito repellent containing DEET, wear sunblock, eat fresh fruit and vegetables every day, lower your stress.

The advice adds up to this:  know your limits.  Federally sponsored research tells us that self-control is ontagious.

The personal-responsibility view of health says, “control your appetites.”

3.  But let’s think about another change:  more people are concerned about the American diet.  As noted last week, the food movement has given us ways to think about eating that go beyond the tiresome story of obesity and hypertension — Beyond Fat and Salt, you could say.

Of course, the main media outlets still tell the food story in Fat-and-Salt language, as the news articles in the NY Times, LA Times, and others show.  It’s the food industry vs. the foodies, or the food industry vs. public health, or the food industry and public health vs. appetites — anyway, somebody against somebody in the name of health.

The media aren’t quite past obesity and hypertension yet.  But as the culture moves beyond obsessive self-inspection in the name of health, no doubt media will, too.


By Philip Alcabes | June 3rd, 2010 | Categories: Behavior, Disease, Health Professions, Narratives, News, obesity, public health, Uncategorized | Tags: , , , , , , , | 2 comments

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