Fouling and Cleansing our Nest; Human-induced Ecological Determinants of Disease

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 hunter-gatherers 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 ComponentsReflecting 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

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 Forehighlanders 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.

Fouling and Cleansing our Nest; Human-induced Ecological Determinants of Disease