Third+Epidemiological+Transition

= Third Epidemiological Transition =

Definition
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The epidemiological transition model explains human disease patterns over the past 10,000 years. The concept seeks to explicate population changes over time. The model is intrinsically epidemiological in nature because such large-scale changes are linked to the patterning of morbidity and mortality of certain populations.

The epidemiological transition model posits that humans underwent three major disease transitions since the advent of agriculture. The first transition traces the emergence infectious and nutritional diseases to the beginning of agriculture and food production 10,000 years ago (Armelagos, Barnes, and Lin, 1996). The second transition, which began in the modern era, was marked by the shift of disease patterns from infectious to chronic and degenerative diseases in developed nations due to improvements in nutrition, public health and medicine. Diseases in this category range from cardiovascular diseases to cancer, and are often associated with longer lifespan and sedentary lifestyles.

The third transition, which started at the end of the 20th century, is characterized by novel diseases, the re-emergence of infectious ones, and their rapid spread caused by globalization (Harper and Armelagos, 2010). In the past three decades, researchers have identified more than two dozen novel pathogens and grappled with the evolution of antibiotic-resistant microbes. With the ease of international air travel, the proliferation of global commerce, and the industrialization of agriculture, such diseases are spreading with unprecedented speed. However, diseases present in the second transition remain prevalent and are rising in certain parts of the world. This presents a significant challenge to many countries facing a dual burden of infectious and chronic diseases.

History
Similar to the shifts in disease trends the model conveys, the concept of epidemiological transition itself went through modifications. Coined in 1971, A.R. Omran came up with the term to describe a shift of disease patterns that influenced “population processes,” i.e.: modernization and the resulting “man-made” diseases (Armelagos, Brown, and Turner, 2005, p. 756). Specifically, Omran used the model to explain the transition from infectious to non-communicable or chronic diseases affecting Europe and North America. Subsequent scholars tweaked the model to include a wider perspective of human diseases and demographic changes in multiple regions or social and political economy contexts.

Armelagos and colleagues (2005, 2010) describe the epidemiological transition in three phases, using the Paleolithic era as a baseline. The first transition took place with the advent of agriculture, about 10,000 years ago. The ability to produce food and the domestication of animals removed human reliance on hunting and foraging. This new-found skill introduced a host of zoonotic diseases and nutrient deficiencies and increased encounters with vectors during farming activities (Harper and Armelagos, 2010). The second transition began in industrialized nations in the past 200 years. The advances in public health and nutrition raised life expectancies, but also brought about a rise in non-communicable diseases such as heart diseases, cancer and Type-2 diabetes.

Most of the world is entering the third epidemiological transition, one marked by novel pathogens, the re-emergence of infectious diseases, particularly strains that are drug resistant, and their ability to spread rapidly through globalization. There are multiple factors at play that contributes to these phenomena: “The emergence of disease is the result of an interaction of social, demographic, and environmental changes in a global ecology and in the adaptation and genetics of the microbe, influenced by international commerce and travel, technological change, breakdown of public health measures, and microbial adaptation” (Armelagos, Barnes, and Lin, 1996, p. 1). Since 1973, the Centers for Disease Control and Prevention has identified 29 new pathogens such as HIV, the Rotovirus and Ebola virus (Barrett, Kuzawa, McDade, and Armelagos, 1998). The discovery and widespread use of antibiotics and other drugs resulted in drug-resistant pathogens, adding to the rise of ‘re-emerging’ diseases such as tuberculosis and Methicillin-resistant Staphylococcus aureus (MRSA). The ability to traverse the world with ease and the global market economy also contributed to the third transition. Diseases can now spread faster across geopolitical borders with air travel; while unequal economic development and poverty intensify the prevalence of such diseases. However, diseases that characterize the second transition remain: many developing countries are now facing a dual burden of infectious and chronic diseases.



Criticism
The model is not without criticism. Disease transitions are not necessarily linear – countries such as El Salvador, Guatemala or Kenya have ‘bypassed’ the second transition and are already facing consequences of the third transition (Harper and Armelagos, 2010). Some regions in the world are facing infectious and non-infectious diseases simultaneously, such as China and India (Dummer and Cook, 2008). The pace of the transition varies depending on various political and economic factors, such as in Japan and Eastern Europe (Harper and Armelagos, 2010).

The model does not include mortality trends that result from accidents, suicide, homicides and other injuries, or captures the complex multi-factorial interplay in the causes of death and diseases (Martinez and Leal, 2003). Paul Farmer, a physician and anthropologist, takes the critique further and holds that the notion of re-emerging diseases only becomes an issue when it “enters the consciousness of the wealthy” (Harper and Armelagos, 2010, p. 686; Farmer, 1999). Diseases such as Ebola, multi-drug resistant tuberculosis and some types of streptococcal infections are labeled as re-emerging only because they have been popularized by mainstream media. The model fails to consider the political economic factors that encourage the ‘re-emergence’ and spread of these diseases. Also, the model seems to rely heavily on the notion of economic development and the concept of “affluent” diseases, which Wilkinson (1994) objects. He posits that health is affected by the proportion of wealth within one society. A model such as the epidemiological transition sometimes gloss over social disadvantage within a region, and it is hard to generalize the health patterning of a population based on the average income reported for a nation or state.

Tuberculosis
Scholars have long suspected that tuberculosis first emerged after the advent of agriculture, but consensus on the origins of the bacterium that infects humans remains inconclusive (Harper and Armelagos, 2010). However, the earliest evidence of human-related tuberculosis came from the Nile Valley, where skeletal remains dating back to 3,000 were found bearing lesions associated with the disease (Daniel, 2005). By the end of the 19th century, tuberculosis had killed 350 million people in Europe and is often associated with poor working and living environments (Armelagos, 2005; Barrett, Kuzawa, McDade, and Armelagos, 1998). It was a disease that killed millions in both Europe and North America during the second epidemiologic transition.

Today, almost a third of the world’s population is afflicted with tuberculosis, and the disease continues to kill in all continents, especially in developing regions. The prevalence of TB – and the effort to control it – demonstrates the interconnectedness of a globalized world. Today’s TB cases also feature a troubling phenomenon: the rise in extensively drug-resistant (XDR) and multidrug-resistant tuberculosis (MDR). Drug-resistant strains emerged through mutations resulting from drug selection pressure, caused by the misused of antibiotics and the weaknesses of public health measures (Gandhi, Nunn, Dheda, Schaaf, Zignol, van Soolingen, Jensen, and Bayona, 2010; Kim, Shakow, Mate, Vanderwarker, Gupta, and Farmer, 2005). Other political and economy factors contribute the ‘re-emergence’ of TB as well. The high incidence rates of TB in developing regions such as sub-Saharan Africa are caused by poverty, the lack of adequate drug therapy and misuse of drugs, and co-infections from diseases such as HIV/AIDS (Kim, Shakow, Mate, Vanderwarker, Gupta, and Farmer, 2005).



H1N1/Swine Flu outbreak
In 2009, the discovery of the novel influenza virus, H1N1, caused massive fear of a pandemic. The virus, which was originally confined to infecting pigs, made an evolutionary jump that allows it to infect humans. Health experts believe the outbreak started in Mexico, and before long it had spread throughout the world through travel. The virus killed several hundred people and sickened thousands. Global health authorities were able to contain the spread in 2010. This video is an example of how world travel can heighten the rapid spread of infectious diseases.

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Related Terms
Globalization Infectious Diseases Diabetes Mellitus

Online Resources

 * World Health Organization breaks down the incidence of tuberculosis according to world regions.
 * The National Institute of Healt's website contains an in-depth explanation on emerging and re-emerging infectious diseases.
 * The United Kingdom's National Health Service's website has a primer on meticillin-resistant Staphylococcus aureus, or MRSA. This includes an explanation of how the bacterium has evolved to become resistant to a type of antibiotic.