Next, we will talk about epidemiologic transitions.
An epidemiologic transition describes changing patterns of population age
distributions, mortality, fertility, life expectancy,
and causes of death.
The human population has gone through four
major disease transitions since the agricultural period began.
The first transition is related to the emergence
of infectious diseases and diseases related to nutrition.
And to the beginning of the practice of agriculture and food production.
10,000 years ago, people became less dependent
on hunting and gathering once they were
able to produce food and domesticate animals.
This shift led to zoonotic disease, nutrient deficiencies,
and increased contact with disease vectors during agricultural activities.
The second transition was a time where human immune systems
and disease-causing organisms both evolved, resulting in a change from major
epidemics of disease to endemic disease.
People developed physical and genetic changes that
serve to minimize the effects of diseases.
The third transition resulted when disease patterns
changed from infectious to chronic and degenerative diseases,
in developed parts of the world due to
improvements in nutrition, public health, and clinical medicine.
Cardiovascular diseases and cancer began to occur more during this transition.
They are often associated with the longer lifespan and a sedentary lifestyle.
The fourth transition started at the end of the 20th century.
When both new diseases and the reemergence of infectious ones occurred
as well as the rapid spread of disease due to globalization.
So let's compare the four epidemiologic transitions.
The first transition started when hunter gatherers began to
practice agriculture and began to live in one place.
There was a transition from few epidemics to major epidemics.
The second transition happened because populations
developed immunologic resistance and disease-causing organisms changed.
There was a transition
from major epidemics of disease to endemic diseases.
The third transition came from improved public health and sanitation.
There was a transition from infectious
diseases to non-infectious chronic and degenerative diseases.
The fourth transition was due to increased globalization.
There was a resurgence and rapid spread of infectious diseases.