HLTC05H3 Chapter Notes -Zoonosis, Scrub Typhus, Epidemiological Transition
ProfessorRhan- Ju Song
Evolutionary, historical and political economic perspectives on health and disease
- William Stewart, a US surgeon testified before congress that eradication of infectious diseases was at hand and will
be wiped out soon. He claimed smallpox, bubonic plague and malaria were thigns of the past. He said it was only a
matter of time till other diseases would be eradicated.
- WHO issued a report in 2001 in which they showed that most of the death especially in third world countries were
due to parasitic and respiratory diseases now. Other deaths due to AIDS, tb and malaria.
- Stewart was unable to judge the potency that such parasitic pathogens and insects would cause more harm then
- Therefore it can be said that humans continue to cause ecological disturbances that inversly accelerate changes in
antibiotic and pesticide resistance, therefore causing death of millions of people.
- The trend of declining infectious diseases and rise of chronic diseases was seen as a result to the the increasing
health and economic developments.
- The changign pattern of disease was the basis of an epidemiological theory porposed by Abdul Omran in 1971. He
observed a change in disease patterns that caused a shift in trend from pathogenic diseases to man made diseases.
- His theory illustrated the role that polution and other by products of the industrial age played in the disease
- Social stratification originally evolved as it brough benefits to emerging elites. Thsu these resources that brought
benefits to few came at the expense of many.
- When organisms appropriate other as continuing sources of food and energy, this relationship is is known as
- Social stratification and within societies and between them is an evolutionary stratergy that we consider –
- Parasitism original reffers to a human social relationship.
- According to oxford dictionary, parasitism is a relationship in which a wealthy patron would pay a person to dine
with and entertain him.
- According to armelagos and collegues, human populations have gone through an earlier epidemiological transition
and are currently going through a 3rd one.
- The shift from foraging to primary food production represented the first epidemiological transition.
- Domestication of plants and animals in the neolithic era caused increase in infectious diseases. Therefore increase in
populations, density, domestication of animals, cultivation and social stratification represented the second
- The second epidemiological transition was originally Omran’s conceptualization about disease pattern.
- Lastly, we are living in the third epidemiiological transition in which antibiotics are loosing their effectiveness. This
period is chracterized by the emergence of chronic diseases.
- He argues that emerging diseases are only discovered when they have an impact on americans
- He also claims that emerging diseases are usually presented as a result of human behavior or microbial changes.
- He critisizes that it is these social changes tha inflluence inequality in an increasingly interconnected world and how
these inequalitites effect the disease process.
In this century, the widening gap between those on the top and the bottom of the social hierarchy occurs both within and
between societies and is greater than ever before in human history. This gap has serious health implications. While disease
and death are inevitable, a major cause of unnecessary, premature, preventable disease and death is extreme poverty.
- Early era species or parasites
- They include: hair and body lice, pinworms, and protozoa
- Souvenier species whose primary hosts are non humans but may accidently affect humans
- Sources of zoonitic disease: insect bites, processign and eating contaminated meat, and animal bites
- Avian tb, leptospirosis, fever, scrub typhus, tetanus, trichinoses are among examples of zoonotic diseases.
First epidemioilogical transition:
- Development of primary food production is the basis of changing disease pattern
- The rapid increase in population size and density, sedentarism, the domestication of animals, extensive ecological
disruption from cultivation and the rise of social and economic inequality are all factors that increase infectious
- The political and economic changes with the development of agriculture created social classes with differential
access to resources, a system that continues to this day.
- Sedentarism increased parasitic infection because of proximity of the living areas to source of waters and the areas
where human waste was deposited.
- The contiguity of habitation to the space where domesticated animals were kept, created a cluster of disease
- Parasites, such as tapeworms associated with domesticated goats, sheep, cattle, pigs, and fowl, infected early
- Humans were considered the source of infections in cattle, sheep and goats.
- The milk, hair, and skin of domesticates, as well as animal dust, transmitted anthrax, Q fever, brucellosis, and
- Peridomestic animals such as rodents and sparrows, which are drawn to human habitats, are also a source of
- Cultivation often exposes workers to insect bites, and diseases such as scrub typhus becomes common
- Dietary defieciencies occurred due to agriculture subsistence for farmers. Which caused infectious diseases.
- Livingstone and Wiesenfeld showed that slash and burn agriculture in West Africa exposed populations to the
mosquito, vector of malaria.
Urban development and disease:
- The impact of contemporary urbanization on health has been studied extensively
- Large settlements increased the already difficult problem of removing human wastes and delivering uncontaminated
- Cholera, a waterborne disease, became a potential problem and lice that carried typhus and the fleas infested with
the plague bacillus
- spread disease from person to person.
- High population densities enhanced the respiratory transmission of the plague and the transmission of viral diseases
such as measles, mumps, chicken pox, and smallpox.
- The rapid urbanization of human populations and expansion into new ecological zones represents one of the most
important forces in the evolution of infectious disease.
- Earlier trade in the Old World and exploration in the fifteenth and sixteenth centuries made inevitable
transcontinental and transoceanic disease exchange that increased the potential for an endemic disease to be
transmitted as epidemic disease in areas of contact.
- Cross-continental trade and travel resulted in intense epidemics
Urbanization in a industrial world:
- The process of industrialization, which began a little over 200 years ago, led to an even greater environmental and
- City dwellers would have been forced to contend with industrial wastes and polluted water and air.
- Slums that rose in industrial cities would become the focal point for poverty and the spread of disease.
- Tuberculosis and respiratory diseases such as pneumonia and bronchitis are associated with harsh working
situations and crowded living conditions.
- In 1800, London was the only city of a million people,
- In 1950, New York City with a population 12 million was the largest megacity (populations over 5 million) in the
world, and at that time, only two of the largest to 10 urban agglomerates were in developing countries.
- The projected increase for the year 2030 is that 60% of the world’s population will be living in urban centers and
that this increase will occur in the less developed nations
- The detrimental effects of industrialization have continued globally as pollution from the industrial production of
commodities has created health concerns.
- The implications of contaminated water, pesticide use and depleted ozone on human health and food production
are significant, for at no other periods in human history have the changes in the environment been so rapid and so
Second epidemiological transition:
- The increasing prevalence of chronic diseases is related to increases in lifespan longevity that have occurred over the
past few centuries.
- the technological advances that characterize the second epidemiological transition often result in an increase in
- The development of the germ theory of disease has been considered as the major force behind the decline of some
- However, others have noted infectious diseases were declining before the initiation of many immunization programs
and therapeutic practices
- Immunicazation led to eradication of smallpox as well as a number of communicable diseases worldwide.