Saturday, February 12, 2011

The Third Epidemiological Transition




# 5309



While those who embrace new age philosophy will likely insist that this is the dawning of the Age of Aquarius, according to well respected anthropologist and researcher George Armelagos of Emory University, we are actually entering the Third Epidemiological Transition.


I first became aware of Armelagos’ concept from reading Dr. Michael Greger’s terrific book Bird Flu: A Virus of Our Own Hatching. Dr. Greger’s book is freely available at the above link, and absolutely worth your time to read. 


Later, following the footnotes from Greger’s book, I found and read:


Armelagos GJ, Barnes KC, and Lin J. 1996. Disease in human evolution: the re-emergence of infectious disease in the third epidemiological transition. National Museum of Natural History Bulletin for Teachers 18(3)


This paper, along with Dr. Greger’s book, made a big impression on me, and has influenced the direction of AFD over the years.  Instead of remaining avian-flu centric, I’ve endeavored to expand the scope of this blog to include many other emerging disease threats.


In a nutshell, Armelagos et al. proposed that the history of human disease could be divided into 4 broad eras marked by three major transitions.


(Note: The evolution of humanity isn’t monolithic or even linear in nature. There remain societies today that still live a nearly Paleolithic existence, and others that remain in largely a pre-industrial revolution age.)

The first era, dubbed the Paleolithic Baseline, depicts  the first few million years of human existence, up to about 10,000 years ago. 


Mankind existed in small, isolated groups as hunter-gatherers where population size and density remained low.  Their sparse interaction with humans and other animals, along with limited range of travel, tended to minimize the effect of infectious diseases.


While diseases diseases and parasites plagued humans, those that required a constant supply of susceptible hosts, tended to die out quickly. 


The First Epidemiological Transition occurred when man moved towards a more agricultural society, about 100 centuries ago.  While increasing food security and nutrition, this transition also introduced several significant disease factors.


In order to improve the land and make it fertile, mankind became less nomadic, and settled into larger population clusters.  Villages grew into towns, towns grew into cities.


Pathogens that once might have died out after infecting a single extended family unit, now had ample opportunities to spread.


And by eschewing the nomadic lifestyle, people stayed in one place and increased their contact with human (and animal) waste, and often contaminated their water supplies.


The domestication of animals brought other disease vectors in close contact with humans.  Q Fever, Anthrax, and tuberculosis all gained access to human hosts.


And even the cultivation of soil, and the clearing of land, exposed people to insect bites, bacteria, and parasites.


As cities grew, and exploration of the surrounding world increased, man spread deadly diseases in ever-greater numbers.   Cholera, plague, influenza, and typhus all became major scourges for humanity.


The Second Epidemiological Transition began roughly 200 years ago, with the Industrial revolution.  


While many of the existing diseases brought forth during the first transition certainly did not go away, new – chronic, non-infectious, degenerative diseases – were added to the mix.


With advances in medicine, sanitation, and technology the average lifespan markedly increased. With that came diseases of age that simply hadn’t been all that common when 40 years was considered a long life (e.g. heart problems, osteoarthritis, cancer)


Technology also brought with it smokestack industries, chemical toxins, working indoors as opposed to out, increased stress, and greater access to less `healthful’ food. 


And with this second transition we’ve seen rises in allergies, asthma, autoimmune disorders, and sexually transmitted diseases as well.


The Third Epidemiological Transition began in the late 1970s or early 1980s, and is hallmarked by newly emerging infectious diseases, re-emerging diseases carried over from the 2nd transition, and a rise in antimicrobial resistant pathogens.


When you combine those factors with an increasingly mobile global population of about 7 billion people, and huge increases in the number of animals being raised for food consumption (often in environments conducive to the spread of diseases), and you have a recipe for explosive growth in diseases.


In a 2010 paper, Armelagos along with Kristin Harper, updated his original paper.  Both papers are well worth reading.


Int J Environ Res Public Health. 2010 February; 7(2): 675–697.

Published online 2010 February 24. doi: 10.3390/ijerph7020675.

The Changing Disease-Scape in the Third Epidemiological Transition

Kristin Harper and George Armelagos



We are, quite simply, living in an age of emerging infectious diseases.  Over the past three decades, dozens of new – mostly zoonotic – diseases have been identified.  


Some have already had a major impact on humans (e.g. HIV, Lyme, XDR-TB), while others remain marginal threats, but may have tremendous potential for greater damage in the future. 


EIDs (Emerging Infectious Diseases) are such a growing concern that in 1995 the CDC began publishing the EID Journal, a highly respected peer-reviewed journal on emerging pathogenic threats.



Yesterday the news wires were filled with stories based on a report issued by the International Livestock Research Institute, that warned of the threat of farm animals spawning new epidemics. 


Excerpts from their press release follow:


Livestock boom risks aggravating animal 'plagues,' poses threat to food security and world's poor

Research released at conference calls for thinking through the health impacts of agricultural intensification to control epidemics that are decimating herds and endangering humans

NEW DELHI (11 February 2011) – Increasing numbers of domestic livestock and more resource-intensive production methods are encouraging animal epidemics around the world, a problem that is particularly acute in developing countries, where livestock diseases present a growing threat to the food security of already vulnerable populations, according to new assessments reported today at the International Conference on Leveraging Agriculture for Improving Nutrition & Health.

(Continue . . . )


These issues aren’t new, of course.  In fact, they have been a major component of flublogia since the beginning.


Maryn McKenna addresses them regularly in her blog, particularly in regards to antibiotic abuse and growing antimicrobial resistance on the farm.


Helen Branswell of the Canadian Press wrote an impressive piece last December for Scientific American on pig farms as Flu Factories, and is interviewed in a 15 minute podcast (How You Gonna Keep Flu Down on the Farm?: Pig Farms and Public Health).


Michael Greger has a Humane Society DVD, also called Flu Factories, which you can view online.



Diseases that might never have evolved fifty or 100 years ago - when Old McDonald had a half dozen sows on his farm -  have a much better opportunity to spread and mutate when introduced into CAFOs (Concentrated Animal Feeding Operations) with thousands of pigs or hundreds of thousands of chickens.



Photo Credit (Wikipedia)


We live in an amazingly complex and interconnected world, where what happens on a chicken farm in China, a pig operation in Belarus, or even at a cockfight in Indonesia can ultimately impact the health of people around the world.


Oceans and long distances are no longer barriers to the spread of diseases. A new virus strain can literally hop a plane in Beijing, and be in Montreal in less than 24 hours.


And that is exactly what happened in 2003 with SARS.


We can no longer afford to think of cholera in Haiti, or dengue in Brazil, or even an outbreak of some new cattle disease in Myanmar as being someone else’s problem.


In this Third Epidemiological Transition, ailments from even the most remote corners of the globe are fully capable of reaching our shores.


Today, our best protection is an early warning system that can tell us when a new disease threat has emerged, or that an old one is gaining momentum. Only then can we possibly hope to muster resources early enough to mitigate the threat.


Which is why much more attention must be paid to global surveillance, international cooperation, and the immediate reporting of human and zoonotic disease outbreaks. 


The spread of infectious diseases can no longer be constrained by oceans or artificial geopolitical borders.


And neither should be our willingness to tackle them.