Selected Readings on Human Health, Disease, and the Environment

The following are responses and summaries of various readings related to Human Health, Disease, and the Environment. 

Linkages Between Climate, Ecosystems, and Infectious Disease

Weather and climate are different ideas in similar fields of study.  Weather is the measurement of temperature, humidity, precipitation, and wind daily whereas climate measures these factors over a long period of time.  Climate is an average and varies with geography and time.   The average temperature of an area decreases by 6.5 degrees C with every 1000 meter change vertically and decreases 5 degrees C with every 1000 kilometer change from the equator.   The range with which temperature fluctuates due to the seasons is greater towards the poles, with much less change experienced near the equator.  There are many climate cycles occurring from yearly to millennially and some occurring as little as every 100,000 years; these oscillations can cause temperature shifts as high as 10 degree C.  Since the Industrial Revolution, and more notably in the last twenty years, the global average temperature has begun to increase yearly and is predicted to continue increasing several degrees in the next century.  The basis for good predictive weather and climate models does not rest solely on the atmosphere but also in surface variations, especially the oceans.  Currently weather prediction is only effective on a timescale of less than two weeks, while climate models are limited to seasonal or greater timescales.  Including the effects of ocean, atmosphere, and land may make climate models sufficient for shorter timescales and weather prediction for greater timescales.  With infectious disease, the number of cases that indicates and epidemic will vary with each particular disease, region, and time.  Emerging disease can be due to climatic or ecological change, which causes a greater number of people to come into contact with a natural reservoir of infection.  Diseases can be transmitted either directly, due to contact with an agent, or indirectly, through a natural reservoir or host.  Many studies of infectious disease use the SEIR framework:  S. The proportion of people who are able to become infected E. Within that same group, those who have had contact with the agent but who have not become infected I.  The number of people within S group who have contracted the disease R. The number of people who have been removed from the original group S due to either death or immunity.   SEIR attempts to account for the many different factors in disease studies such as population size and density, demographics, connectivity patterns, and immunity.  Diseases and natural reservoirs have environmental conditions that are both favorable and not for the spread of particular diseases which include precipitation, temperature, humidity, and ultraviolet radiation.  Most diseases are sensitive to changes in temperature with regards to their dissemination, replication, and movement.  Climate change over the long-term may result in increased intensity and occurrence in extreme weather events, where the direct impact is obviously more deaths due to disasters, though potentially and indirectly an increase in infectious disease outbreaks.  The diseases associated with flooding are well known while droughts are not nearly as studied, though a disease would not affect a crisis area should it not have been present in the system before the extreme event and had not be introduced.  There are many other factors that influence disease dynamics including land use, migration of disease and hosts, the societal makeup of populations, and public health services.

Selected Readings on Human Health, Disease, and the Environment

The following are responses and summaries of various readings related to Human Health, Disease, and the Environment. 

Under the Weather: Executive Summary

Changes in climate can affect the movement pattern of infectious diseases due to the fact that the microorganisms and their carriers are equally prey to changes in temperature, moisture, and other environmental changes, though other diseases such as HIV or Hepatitis do not have the same causal relationship with the environment because they are transmitted through direct human interaction.  In 2001 the National Research Council was asked to study the issue of the environment, its change, and the possible effect on human health and disease.  Specifically they reviewed: 1. possible connections between the variations of time and space with respect to the climate and the transmission of disease 2. Studying the possibility of creating warning and surveillance systems for climate affected diseases 3. Investigating possible future studies on the relationship of disease, climate, and human health.  Multiple disciplines, whom usually do not work together or in similar fashion, were required for the project due to the multidisciplinary nature of the issue.  Temperature, precipitation, and humidity directly and indirectly change the life of many infectious diseases and their vectors, though they are also affected by the sanitation and health services provided within a region, the density of human or vector population, changes in ecology, and organism travel habits.  Many studies have been conducted on the effect of climate change on disease however they have not been able to account for the many variables that lie under the function of diseases and are not reliable for predicting future change.  The impact of climate change on disease has yet to be well sorted out, though many believe that global warming could have an adverse impact, however human adaptations and health services could potentially prevent or reduce such impacts.  New diseases may emerge or old diseases reemerge in newly evolved forms due to ecosystem changes.  Studies of the relationship are dependent on local, small scale which make it difficult to enlarge the results to a larger scale relationship.  Long term climate change could have a vastly different effect than short term climate change such as ENSO.  Advances in technology will allow for the analysis and more detailed studies.  Historically the strategy has been to survey and respond to disease threats, but in the future hope is for a predict and prevent strategy.  Climate forecasts and observations could be used in identifying high risk areas and preventing the or reducing their occurrence.  A general understanding of the relationship may allow for some form of early warning system at a low cost, but some may require a more costly prediction system, depending on the particular disease and region.  Systems will only be beneficial if the operating agency has the sufficient resources to act upon their results.  Climate forecasts must also be combined with meteorological, ecological, and epidemiological systems to work properly as an advanced warning system.  Public health officials and government agencies must work in conjunction with one another for the systems to have their desired effect.  The research into these relationships has only just begun and has a long road to traverse before it can become effective.  The data set involving disease, climate, and geography need be greatly increased for prediction models to even be a possibility.  The interdisciplinary collaboration in universities and private institutions need be greatly increased.  New disease will always have the upper hand in the battle, however the goal should be to reduce people vulnerability to disease.

Selected Readings on Human Health, Disease, and the Environment

The following are responses and summaries of various readings related to Human Health, Disease, and the Environment. 

Life Support: Environmental Endocrine Disruption

Chemicals found in the environment have effects on fetuses much more than on adults because even the slightest of changes in the hormone levels of the undeveloped human can have very drastic consequences.  These chemicals are able to directly bind to or block the hormone receptors making gene transcription initiated by the hormone receptors erroneous.  Similar exposure levels in adults do not show nearly as great physiological changes.  Possible abnormalities include feminization of males, abnormal sexual behavior, birth defects, altered sex ratio, lower sperm density, decreased testis size, altered time to puberty, cancers of the mammary glands or testis, reproductive failure and thyroid dysfunction.  Studies that have been conducted have difficulty in consistency due to the time between exposure and the resultant effects, such as cancer showing decades after first exposure, and finding a control population, since any control population is going to already have some degree of exposure.  Organochlorine contaminated food has been shown to affect the brain development of lab animals and children exposed have shown delayed psychomotor development and increased distractibility.  Some pesticides result in decreased brain density of some nerve receptor types and hyperactive behavior.  Because hormones act at such low levels even the slightest of chemical exposure can result in very bad developmental effects.  One of the main failures of past studies is their focus on the individual rather than the population as a whole, though the size and seriousness of the health threat is still uncertain.  Work by the International Joint Commission, United States and Canada, has begun striving towards the elimination of volatile chemicals.  They hope for zero discharge of chemicals from human activities, analysis of chemical effects from creation to destruction and afterwards, and reversing the burden of proof from showing that a chemical is harmful to showing that a chemical is not harmful before it is allowed to be used.

Selected Readings on Human Health, Disease, and the Environment

The following are responses and summaries of various readings related to Human Health, Disease, and the Environment. 

Life Support: Urban and Transboundary Air Pollution

Since the Industrial Revolution people have been studying the effects of pollutants on lung disease.  During the Industrial Revolution entire communities of North America and Europe fell seriously ill or died from air pollutants.  These episodes were a result of air stagnation, which increased the concentration of pollutants in the atmosphere, more specifically those of sulfur dioxide and suspended particulates.  Because of these episodes scientists and governments began studying the adverse effects of pollution – identifying the sources of pollutants, and discovering exposure-response relationships, eventually leading to controls against pollution.  Because the air cannot be contained pollution is able to travel across borders.  Poorer nations generally have a greater problem with pollution than wealthier ones, especially due to the heavy use of coal for power and heating.  The countries which have found ways to reduce the emissions of pollutants from industry, power plants, and automobiles have created new problems via the formation of acids and ozone from their outputs.  The most common adverse health effects due to pollution are caused by sulfur dioxide, particulates, photochemical oxidants, ozone and nitrogen dioxide, and carbon monoxide.  Sulfur dioxide is a result of the combustion of fossil fuels such as coal and crude oil, generally affiliated with power plants and oil refineries.  Great reductions in the measurements of sulfur dioxide and related pollutants were achieved after the Clean Air Act of 1970s America.  However, the tall stacks which were implemented merely send the pollutants higher into the atmosphere where they are able to change into acid aerosols.  Particulates are the result of industrial activity which put off particles into the air which do not easily dissipate.  Particulate counts have been shown related with an increase in mortality rates.  Finer particles have been shown to be much more detrimental to respiratory systems than more coarse particles. In areas with high particulate levels deaths in children from respiratory illnesses is equally high.  In the developing world only infant diarrhea accounts for more deaths in children under the age of five.  Ozone and nitrogen dioxide are most commonly produced by sunlight on the output of automobiles.  When the amount of sunlight is greatest during the summer the greatest amount of ozone is produced.  The safest area to avoid exposure to ozone is indoors because ozone seems to be unable to contact surfaces chemically unchanged.  Carbon monoxide is another major automobile emission.  Many major U.S. cities have exceedingly unhealthy levels of carbon monoxide.  Carbon monoxide impairs the transport of oxygen throughout the cardiovascular system, the effects of which can be headache, dizziness, fatigue, and even death.  Poorer nations who use wood, crop residues, animal dung, and other carbon based fuels for cooking and heating are especially at risk for indoor pollution.  The government has failed greatly in studying the problem of pollution indoors.  Nations need to work together in finding solutions to the ever-growing pollution problem, as it is a global issue not only local one.

Selected Readings on Human Health, Disease, and the Environment

The following are responses and summaries of various readings related to Human Health, Disease, and the Environment. 

Meat can be Murder…

Vegetarianism has potential health benefits such as a lowered risk of heart disease and cancer, however vegetarians are not the only ones who can achieve these advantages.  As far as public health is concerned, simply reducing the intake of saturated fats would have a great impact.  The total meat consumption of the average American was fifty seven pounds more in 2000 than in 1950.  The foods that contain unhealthy amounts of saturated fats raises the risk of heart disease and stroke and increases cholesterol.  Also, cooking some meats at high temperatures, required for the elimination of some bacteria, can produce chemicals believed to be potential human carcinogens.  High intake of well cooked meat has been shown to increase the risk of developing colorectal and breast cancer.  Eating much charred or burned meat is very likely unhealthy.  Consuming more meat than is necessary for the human body will merely cause the body to eliminate it through the urinary tract putting additional strain on the kidneys in order to metabolize it.