Thursday, June 5, 2014

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. 

Six Modern Plagues: Introduction
Fifty years ago the people of the west believed that humanity was nearing a point where no longer would we need to worry about sickness.  Medicine had developed to a point where it seemed that it had an answer for every infectious disease in existence.  In reality, though, the late nineteenth and twentieth centuries were merely the calm before the storm.  Today new diseases are being discovered at a rate faster than any previous time in history.  Many of these are diseases which have long existed in other species but due to humanity’s changing of its environment they are now jumping ship from their previous bodies to us.  This change is occurring because people are now invading land which they have never before occupied; forcing bacteria and viruses to evolve and adapt to their newfound hosts.  Evolution usually occurs naturally over long periods of time but in today’s age the great ecological change being caused by humans is speeding up this process.  Not only are these new diseases on the rise, but old diseases which have been lying dormant are beginning to re-emerge.  Diseases such as small pox and leprosy were not long ago thought to have been completely eradicated but they are beginning to return and in strains which the old cures and vaccines have no affect on.  The problem is that the speed with which our microbial enemies evolve and adapt is increasing and humanity is directly responsible.  Our ever increasing destruction of natural habitat, invasion of areas where we have not previously inhabited, and shift from a sedentary lifestyle to daily transcontinental travel is merely speeding up this process.  A change in dominators has already begun.  We will lose the ability to regain upper hand if we do not soon change our ways.

Disease Basics
A disease is any condition which can cause negative change in a system.  Diseases are often the result of actions by some other living organism.  These organisms’ (bacteria, viruses, fungi, protozoa, helminthes, and prions) only desire to reproduce, as is the goal of all living organisms.  A disease, or pathogen, invades a host (in this case a person)via transmission from a vector (carrier), direct contact with the agent, or acquisition through air or water or other similar medium.  Most pathogens make permanent home, reservoir, in an agent without ever damaging the system or being transmitted to another host.  When a pathogen is introduced into a system it is thereafter considered an antigen.  Antigens illicit a response from the immune system of the host.  Once in the system, antibodies, proteins, begin to be produced which will identify, neutralize, tag or destroy the antigen.  The dose response is the level of response by the immune system cause by differing amounts of antigens.  Often times a system may have obtained immunity, enough biological defenses to avoid infection or disease, through genetic inheritance or a previous encounter with the pathogen. Herd immunity occurs when a significant portion of a population has obtained immunity from a pathogen (such as polio or small pox in late 20th century America).  Immunity does not imply that a similar pathogen will not be effective later on.  Pathogens are living organisms which are able to evolve just like others.  Pathogens, however, often evolve at a much faster rate due to their usually high reproductive rates, enabling for genetic mutations to occur more often. 

Why This Class
New diseases are emerging or old diseases re-emerging due to human activity causing change in the environment. In the 1970s, when global travel was starting to become so easily accessible, the emergence, resurgence, and redistribution of once secluded diseases began to occur.  Since 1980 over thirty new emerging diseases have been identified: these are diseases that had not previously existed, or at least had not yet been encountered by significant populations of man.  These diseases have appeared on the radar due to man’s change in its interaction with the environment.  Alternation or contamination of the environment by man can lead to new disease or health concerns (mans destruction of the ozone leads to a greater risk of UV radiation, which may cause skin cancer and other ailments, and has also caused a rise in malaria related deaths possibly related to an increase in the global temperature).  Because humans evolve slowly over thousands of years their connection of species of pathogens from Asia to America enable the pathogens to evolve at a much faster rate than normal therefore leaving humanity and other much slower evolving organisms at risk.  The increased density of human populations does not help with the disease problem.  A greater population in a smaller area makes communicable diseases all the much more dangerous.  It is necessary for the environment, climate, etc. to change over time on our planet for the it to continue to function, but our actions are causing the change to occur at a much faster rate than nature had intended and it will eventually catch up to us.

HIV originated from chimpanzees in the western part of Africa.  The disease evolved from the simian immunodeficiency virus which occurs in species very closely related to man.  Chimpanzees currently infected with SIV may, which do not show sickness, may allow us to find a cure for HIV.  Some of the viruses are the result of genetic recombination in chimpanzees prior to human infection.  The original infection of the virus is believed to have resulted when hunters made contact with the blood of an infected chimp in western Africa.  This particular species is believed to have contributed to no less than three cross-species diseases and because they are still hunted may yet cause more.

Smallpox emerged in human populations some time around 10,000 B.C.E.  The first outbreak of smallpox is believed to have occurred sometime between the first century B.C.E. and first century C.E.  The Antonine Plague of 165-180 C.E. is the first likely appearance in great amount of smallpox.  In the 20th Century alone smallpox was responsible for 300-500 million deaths worldwide.  The World Health Organization declared in 1979 that smallpox was no longer of concern.  The last case of the disease occurred in 1978 England.  Smallpox is the only human disease to have been completely destroyed.

Readings above may have been drawn from the following sources:
Six Modern Plagues and How We are Causing Them, Mark Jerome Walters; Shearwater Books, 2003, ISBN 155963992X
Life Support, The Environment and Human Health, Michael McCally, editor, MIT Press, 2002, ISBN 0-262-63257-8
Rx for Survival,  Philip Hilts, Pengquin Books.  ISBN 0-7394-6974-6
Emerging Infectious Diseases,  Stuart A. Hill, Pearson Eductation Inc., publishing as Benjamin Cummings.  ISBN 0-8053-3955-8
Under the Weather:  Climate, Ecosystems and Infectious Disease, National Research Council, National Academy Press.  ISBN 0-309-07278-6

This article originally written September 3rd, 2008 for OU IPE 3913 - Human Health, Disease, and the Environment.

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