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Infection and chronic disease.
The health sciences have generated great advancements over the past two centuries.
The prevention of waterborne transmission of diarrhoeal diseases alone saved
the lives of at least 10 percent of the residents of prosperous countries.
The invention of antibiotics has allowed physicians to cure rather than
console patients with lethal bacterial diseases such as ammonia.
The widespread use of vaccines has blocked
the circulation of deadly bacteria and viruses.
The deadliest virus of all the agent of
smallpox has been eradicated from the human population.
The discovery of essential dietary components vitamins has prevented
tremendous amounts of suffering and disfigurement
from diseases such as scurvy and rickets.
All of these accomplishments depended on an understanding of
disease causation or at least in insightful guess about what causes disease,
most of these accomplishments resulted from application of the germ theory.
The idea that diseases can be caused by parasites too small to be seen with a naked eye.
It makes sense that an understanding of
disease causation would be central to the advancement of medicine.
Once the cause of a disease is understood,
it may be blocked or eliminated,
and the disease may be prevented or cured.
Considering the tremendous importance of understanding disease causation
the great technological sophistication that has
been applied to medical problems in recent decades,
one would think the causes of virtually all human diseases would now be well understood,
but this is not the case.
Modern medicine has a good understanding of
disease causation for only about half of all human diseases.
Nearly all of these diseases of uncertain cause are chronic,
it develops slowly in a person and persist over long periods of time.
These chronic diseases of uncertain cause
include the big killers of prosperous countries.