Download Заголовок слайда отсутствует

Fouling and
Cleansing our Nest;
Human-induced
Ecological
Determinants of
Disease
John M. Last, MD
Faculty of Medicine,
University of Ottawa
“Changing patterns of disease are
related to the ways we interact with
ecosystems and the earth's life-support
systems with which we are
interdependent. Human actions are
responsible for some, perhaps even
most of the recent changes, for the
worse as well as for the better, in the
pattern of infectious diseases.”
John Last, 2001
The Role of Epidemiology
Epidemiologists have contributed to our
understanding, so it is appropriate for an
epidemiologist to discuss the ecological basis for
historical changes in the impact of disease; and to
speculate on what might happen in the future.
Epidemiology is the basic science of public health.
Epidemiologists study communities rather than
individuals. We look for order underlying seemingly
chaotic disease outbreaks, wherein it can be difficult
even to distinguish effect from cause, let alone identify
causes and control them. Our ultimate aim is to
prevent disease, disability and premature death.
The Sanitary Revolution and
the Ascendancy of Public
Health
1. The sanitary revolution produced
the greatest transformation in the
pattern of disease that the world had
known since nomadic huntergatherers settled in permanent
villages, and ultimately developed
modern urban industrial communities.
The Sanitary Revolution and the
Ascendancy of Public Health
2. The Victorians had a phrase for it, "filth
diseases.[5]" These disease mostly were, loosely
speaking, due to the filthy living conditions that
prevailed in the otherwise prosperous industrial
cities in Europe and North America in the second
half of the 19th century. Occasionally these
endemic causes of premature death were reinforced
by great epidemics that cut a swath through the
population: influenza, croup, diphtheria, smallpox,
relapsing fever, typhus.
The Essential Components
Reflecting on the sanitary revolution of the late 19th
century and the rapidly changing attitude towards
cigarette smoking in the late 20th century, led me to
define a framework [10] that must be in place for us
to control all health problems:
•
•
•
•
Awareness that the problem exists
Understanding its cause
Capability to control the cause
A sense of values that the problem
matters
• Political will
Koch
identified
tubercle
bacillus
Streptomycin
introduced
Vaccination
available
Health as Harmony
One of my definitions of health
[13] is:
A sustainable state of
equilibrium (harmony)
between humans and other
living things with which
we share the ecosystem.
Health and Disease as Byproducts
of Technological Change
• Some changes in
population health, for
the better and for the
worse, have occurred
as accidental
byproducts of changes
in the relationship of
humans to their
environment. Here are
three examples:
Health and Disease as Byproducts
of Technological Change
Health and Disease as Byproducts
of Technological Change
Lifestyle Diseases
The transformation in disease patterns
in the second half of the 20th century
has been less dramatic than that in the
second half of the 19th but
nonetheless profound. In the 1960s
we began to identify causes of
premature death and disability due to
ways we behave [14] -- "lifestyle
diseases" or "diseases of civilization."
Human Activities and
Changing Patterns of Infection
Development of antibiotics has not produced
a disease-free paradise on earth. Control of
the lethal infectious diseases may be
evanescent: some are returning in antibiotic
resistant strains, their virulence and
infectivity (notably of tuberculosis and
syphilis) potentiated in the presence of HIV
infection. And more than 30 new pathogens,
some terrifyingly lethal, have been identified
since the 1970s [15].
New Variants of Old Diseases
Consider the ecosystem of a woman's
vagina. Rising numbers of career
women since the 1960s created
markets for several innovative
products: designer briefcases, smart
business clothing and matching
stationery... and super-absorbent
vaginal tampons that a busy working
woman could wear all day.
New Variants of Old Diseases
On a November night in 1951 in
England, I saw many young men
from a nearby US Army Airforce
base, who all together collapsed some
hours after eating a turkey cooked in
the USA, and flown across the
Atlantic for their Thanksgiving feast.
That was an unforgettable night.
Hazards of International
Trade and Commerce
There can be unexpected hazards of international trade
and commerce. In the early 1990s, epidemic Asiatic
cholera struck the Pacific coast ports and river
estuaries of South America in Peru, Ecuador, and
Colombia. The cholera vibrio got there in bilge or
ballast water on ships from the Bay of Bengal. These
ships released their contaminated water at the same
time as an El Nino southern oscillation (ENSO)
caused a "red tide" of zooplankton to proliferate in the
warmer-than-usual coastal seas. Zooplankton are a
symbiotic host for the cholera vibrio.
Resistant Strains of Pathogenic
Micro organisms
The saga of human encounters with microbes has
taken a new twist. For 50 years we have been at war
against common pathogens like the strep, staph,
pneumococcus and gonococcus. Each time we think
we have a wonder drug that will kill them all,
inexorable laws of Darwinian evolution operate;
microbial generations are a few minutes or less; so
these common and often dangerous pathogens rapidly
evolve strains resistant to antibiotics that
microbiologists and pharmacologists may have spent
years developing.
Newly Emerged Pathogens
Almost all of the 30 or more new
infectious pathogens identified in the
last 25 years are dangerous and many
are lethal. Their ecology, natural
history, epidemiology, and means to
control them are often elusive. These
diseases demonstrate that ecology,
ecosystem health, human health and
human behaviour are inextricably
intertwined.
The HIV/AIDS Pandemic
The first cases of a fatal disease
characterized by wasting, pneumonia due
to opportunistic organisms, and immune
deficiency, were identified in Los Angeles
and New York in 1981 [23], and the
condition was named Acquired
Immunodeficiency Syndrome -- AIDS. The
acronym became a word as the scale and
severity of this terrible new pandemic
disease became apparent.
The HIV/AIDS Pandemic
The pandemic of HIV/AIDS
produced more than 40 million
infections, 10 million cases of
AIDS and 9 million deaths by
January 1, 2000.
Tropical Hemorrhagic Fever
Viruses
Occasionally we encounter dangerous new
organisms, sometimes extremely lethal ones
like those causing Lassa and Ebola fever, two
deadly varieties of hemorrhagic fever. Lassa
fever is transmitted to humans by small rodents
that may be the natural host of the virus, and
whose habitat includes village huts in
equatorial Africa [26]. The habitat, natural
history and epidemiologic features of the Ebola
virus remain almost unknown.
Transmissable Spongiform
Encephalopathies
Among 30 or more recently identified pathogens,
the most fascinating are those that cause
transmissable spongiform encephalopathies
(TSEs). These diseases destroy brain tissue. They
include Creutzfeld-Jakob disease (CJD) and kuru,
discovered among the Fore highlanders in New
Guinea in the 1950s and shown by Gajdusek [27]
to be transmitted by eating the brains of tribe
members who had died of the disease. Kuru
proved that eating people is wrong.
Transmissable Spongiform Encephalopathies
Bovine spongiform encephalopathy (BSE) or "mad
cow disease" proved that it is wrong to give animal
protein to herbivores. This disaster was caused by
misguided application of animal husbandry. It seemed
a good idea at the time, to supplement the feedstock of
dairy and beef cattle with meatmeal, a little animal
protein to raise their protein intake. It was believed
that this would increase milk yields and produce better
beef. For a few years it looked as if it might work.
Alas, the carcases included sheep that had died of
scrapie, another TSE, and soon there was a devastating
epidemic of BSE in Britain [29].
Health Impacts of Global
Change
The largest ecosystem of all is the
biosphere, the earth's life-support system,
a very complex closed system. Until
recently it was assumed that this could
self-correct manmade disruptions. That
assumption is wrong, but regrettably it
persists among powerful but short-sighted
industrial and commercial interests and
the political leaders who do their bidding.
Health Impacts of Global
Change
Global warming is a very serious problem
[34]. The 2001 Report of the
Intergovernmental Panel on Climate
Change (IPCC) revises upward the
estimates of the severity of geophysical,
climatic, and other adverse effects. The
earth is getting warmer than at first
thought, and getting warmer faster.
Health Impacts of Global Change
The geophysical processes are insidious, but likely to
accelerate in the next 50-100 years. Unless we take
immediate steps to mitigate harmful processes,
especially uncontrolled emission of carbon gases due
to combustion of gasoline and coal, the next
generation and those that come after it will suffer
heavily for the misdeeds of our own and several
previous generations. Of all the human induced
ecosystem changes affecting human health, this is the
most likely to cause permanent harm to humans and
all other living things with which we share the earth.
Things to Come
What might happen in the next 50-100 years? I can
offer several suggestions, mostly rather gloomy
ones:
1. We can expect more new diseases to emerge,
seemingly out of nowhere in some instances, in
others more predictably out of regions such as
tropical rainforests into which humans are
encroaching. We can expect also that many diseases
that now respond to antibiotics will cease to do so as
antibiotic-resistant strains proliferate.
Things to Come
3. Famine, or serious food shortages, are likely,
even without the climatic upheavals that are an
expected consequence of global warming. These are
an integral part of environmental stress and the
scarcities it induces, and an inevitable sequel is
armed conflict [38]. Wars almost always bring
further environmental devastation, widespread
misery and suffering, mainly among non-combatant
children and women. War is perhaps the greatest of
all public health problems [39].
Things to Come
5. Finally, we should always
"expect the unexpected" -which might include a scenario
containing "none of the above"
but something altogether
different -- though I can't
imagine what that might be.
Conclusion
Human activities of many kinds, including some
innovations of modern civilized living, can
improve or harm health. One conclusion from this
is the need to consider carefully all possible
consequences before adopting innovative
practices, processes or procedures. We tend to be
easily and uncritically infatuated by anything new
and different. The medical profession is especially
prone to this vice, and has a long history of
disasters to show for it.