emerging infectious diseases, science, and ecology 
Author Message
 emerging infectious diseases, science, and ecology

I thought some of this might be of interest. The entire
transcript is much longer.

Richard Levins, PhD:
Why was public health caught by surprise by new and
resurgent disease?

Excerpts from lecture transcript:
Spring 1996 Seminar on Emerging Infectious Diseases,
Emerging Infections Information Network,
Department of Epidemiology and Public Health,
Yale University School of Medicine.

Complete transcript at:

http://www.***.com/

*****

About 25 years ago, the doctrine of the epidemiological
transition became popular.  This was the idea that
infectious disease had been{*filter*}ed in principle.
Infectious diseases were declining, and the medical
problems of the future would therefore be chronic and
degenerative diseases.  This had important and immediate
consequences.  Medical students were told not to go into
infectious disease, it was a dying field.  The
epidemiology department at Harvard went over completely to
the study of heart disease and cancer.  So it was a
decision that carried a great deal of importance.
Infectious diseases were clearly still around, but it was
believed that we knew how to deal with them, and it was a
matter of time before they would all disappear.  Then
cholera returned in the 1960s, spreading out from India to
Indonesia.  In the 70's it reached Africa, in the 90's,
South America.  Malaria came back after declining in the
50's.  In Sri Lanka, almost disappearing, it returned with
a vengeance.  We had Lyme disease in eastern North
America, toxic shock syndrome, cryptosporidium hit
Milwaukee with some 400,000 cases in the 90's.  There is
an increasing frequency of fish poisonings, of chronic
fatigue syndrome, Lassa fever, Legionnaire's disease,
Ebola, Rift Valley fever spread to Egypt.  Meningitis-B
has been increasing on a world scale, hepatitis-C.  Of
course, AIDS is the most dramatic example.  The
hemorrhagic fevers in Venezuela, Bolivia, Argentina.  The
hantavirus in New Mexico.  Erlichiosis, which is spread by
the same tick that spreads Lyme disease.  The return of
dengue and yellow fever, and so forth.  So it was clear
that the expectation that infectious disease was on the
way out didn't work.  There was a mistake there someplace.
 And we have to look at that mistake and figure out
something about it.

****

So now, if there are good plausible reasons why diseases
should be disappearing and yet they didn't, what was wrong
with the argument?  Let's go back to the first
proposition, the extrapolation that infectious diseases
had, in fact, been declining.  This was true over a period
of 100 or 200 years.  But it was too narrow a frame of
reference.  If we look at the broad sweep of human history
instead, we see a very different kind of picture.  In
periods of major upheaval, of social change, environmental
change, migrations of population, ecological change,
changes in vegetation, there will also be epidemiological
changes. The first recorded, confirmed case of a pandemic
of plague hit Europe in the sixth century at the time of
the break-up of the Roman empire.  It came back again in
the four{*filter*}th century during a crisis of feudalism when
the Mediterranean coast had already been deforested.
Deforestation was increasing in England.  The burden of
exploitation of the serf population had intensified.
There were mass escapes from serfdom, populations moving
eastward in Europe into the forests of the Ukraine and
Poland and so on.  The biggest epidemiological event that
we know of in recorded history was the conquest of the
Americas, where the introduction of European diseases to
the indigenous population resulted in a decrease of as
much as 90 percent in the Native American population
during the first two centuries of European conquest. So
then, as against the notion that history is one of the
progressive disappearance of disease, we have to
substitute the idea that diseases come and go, and that
any major change in the conditions of disease, in the
environment, the demography, the politics, the economics,
will carry with it at least potentially major changes, as
well, in the epidemiology.

*****

The argument that we had all of these nice, shiny, new
weapons to conquer disease did not take into account,
first of all, the responsiveness of nature, the
evolutionary challenge that an antibiotic or a drug
represents to a parasite, means that all of its genetic
variation, all of its natural selection be focused on
finding a way around that particular therapeutic method.
Nevertheless, we tended to think of the control of
diseases, the treatment of disease, in terms of finding
the right molecule for each problem, a one-to-one
correspondence between problems and solutions.  This
represented a kind of magic bullet approach to medicine
parallel to the magic pesticide approach in agriculture
which also made it difficult to recognize that nature does
things on its own.  That whenever we do something, there's
an active response.  And what happens in a bottle in
killing an insect or a pathogen is not what's going to
happen in the field when you apply that method widely.
And one of the observations that came about fairly early
is that when we use pesticides, the natural enemies of the
pests tend to suffer more than the pests themselves.  The
reason for this is not that the natural enemies, the wasps
and the flies, are physiologically more sensitive to
pesticides, but rather their location in the ecological
structure.  Visualize a simple system in which there's a
pest and its natural enemy.  The pest population increases
the population of its natural enemy, the natural enemy
reduces the pest population.  Now we come in with a
pesticide.  The pesticide kills both species.  So there's
a negative input, both to the natural enemy and to the
pest.  Now this negative input becomes translated into a
negative input to the natural enemy.  You multiply the
effects, a negative effect on the pest times a positive
effect of the pest on the natural enemy is a negative
effect on the natural enemy.  That is, we're poisoning its
food. At the same time the natural enemies are being
poisoned directly. Therefore, by both pathways, the
natural enemies of a pest are being destroyed.  On the
other hand, the pest is getting mixed messages.  It's
being poisoned directly, but also its predator is being
poisoned.  So one path is negative, and the other path is
positive.  They may cancel each other, and all too often
we find the pest populations increasing and their natural
enemies diminishing.  This kind of evolutionary argument,
ecological argument, was missing from the experiments in a
bottle where you simply demonstrate that a pest is
vulnerable to a pesticide.

*****

So the commoditization of knowledge is one of the factors
preventing the kind of holistic, integrated epidemiology
that we need.  Another factor is the social organization
of employment in science.  Increasingly what is happening
is that scientists are becoming scientific manpower.  They
are investments, either by corporations or by industry,
and when you calculate investment, you first of all look
at the probability of getting a result, you want the sure
thing.  The research division of a chemical company has to
compete with other divisions of the company for investment
money.  They have to be able to say that investing in
research in a new antibiotic or a new pesticide will be at
least as lucrative as an investment in opening a second
hand car dealership or bribing a military government or
improving the engineering capacity, the quality control in
the plant, or increasing sales effort, or in covering up
toxic side effects.  All of these are equally valid
investments from the point of view of a board of
directors.  So therefore, the head of the division of
research has to be able to prove that the investment in
that division will be at least as promising and at least
as reliable, have at least as big a market, and therefore
tends to push researchers within industry toward the sure
thing, never really posing the question, how can human
knowledge be best applied to reducing hunger, but, rather,
how can oil be best turned into something we can sell
farmers on a large scale.

Within universities, the pathways are somewhat different.
Within universities, there is a tendency to increasingly
treat scientific personnel as other kinds of laborers, and
the downsizing that's affected the automobile industry and
the steel industry is also affecting universities with an
increased proportion of people who are in temporary
appointments, only partially covered by salaries, sent out
to look for grants, and so forth.  Now, when this happens
and when students are accumulating debts at Harvard at a
rate of at least $15,000 a year, there is also a very
strong pressure to focus on the sure thing, not to take
intellectual risks, to subcontract a piece of somebody
else's grant, and then turn the crank and come out with a
result which is sure to be something, even though perhaps
not very exciting.  So the social changes taking place
within our profession are mitigating against the kind of
interdisciplinary diverse kind of work just at a time when
the intellectual necessities of preserving health and the
practical urgencies in agriculture and medicine are urging
a greater kind of recognition of complexity.

****

.... in the border region between Thailand and Cambodia,
where gem miners are coming from all over Southeast Asia,
there's an area of very intense malarial infection.
People bring their own strains of plasmodium from all over
the region.  They're working very intensely, expecting to
get rich within a few weeks.  During this time, if they're
feeling lousy, they can buy some drug in the market
without a prescription.  When they're feeling less lousy,
they can forget about it.  Thus, creating ideal conditions
for the evolution of the malarial parasite.  You have a
mixture of strains, enough mosquitoes so that the
intensity of transmission is high, enough people who are
infected, so that an individual mosquito may be carrying
two clones of gametocytes at the same time, so that there
can be recombination in the mosquito. Conditions of
varying selection intensity, so that parasites are
surviving.  And a sense of urgency because of the land
mines, so that people are worried about being blown up in
the next few hours rather than getting malaria on time
scale of weeks to months.  And that's a particular
environment, then, ideally suited for the evolution of
drug-resistant malaria.

****

Finally, we come to the major dilemma, which is that while
the intellectual requirements of our discipline push us
towards a transdisciplinary, integrative epidemiology, the
social organization of science and the economic
rationality of the administrators of science are
preventing us from doing this, forcing the disciplines to
be more separate, demanding research projects to be more
narrowly focused, urging students to get through in a
hurry on a sure thing.  So we have a conflict here within
the development of science, and the outcome is still in
doubt.  So it's a problem that we all have to intervene
in, in order not to be passively victims of processes
beyond our control. And in that sense, then, an
integrative epidemiology capable of facing the enormous
health problems of our species requires us to intervene
also in the structure of science, to be participant
observers, examining as questions, where does the agenda
of our science come from?  How come we are doing the
things that we're doing and asking the questions that
we're asking, or not asking the questions that we are not
asking?  This requires, then, a self-consciousness in the
development of an epidemiology that is, again, unfamiliar
and perhaps uncomfortable to people trained in the
laboratory sciences.  And yet, it seems that it's
increasingly necessary for us in order to face up to the
contemporary responsibilities.

(end)



Sat, 08 Jul 2000 03:00:00 GMT
 
 [ 1 post ] 

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