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What were early conceptions of the cause of disease?
BIO 550 Discussion Early Concepts Of Disease

What were early conceptions of the
cause of disease?

Discussion 2

Develop or illustrate a timeline of
epidemiologic milestones in public health. What is one of the most significant
milestones to you? Why?

Hunter-Gatherers
Ten thousand years ago humans were hunter-gatherers. They had a short life span, but not because of epidemics; their primary problem was just finding enough food to eat. They lived and traveled in small groups and hunted and foraged for food. Their mixed diet was probably fairly balanced and nutritionally complete. Since they lived in small groups and moved frequently, they had few problems with accumulating waste or contaminated water or food.

Mythology, Superstition, and Religion
Early explanations for the occurrence of disease focused on superstition, myths, and religion. Primitive peoples believed in natural spirits that were sometimes mischievous or vengeful. The Greeks believed that the god Jupiter was angry about man accepting the gift of fire. The story is long and complicated, but Zeus crammed all the diseases, sorrows, vices, and crimes that afflict humanity into a box and gave it to Epimetheus, the husband of Pandora. Mercury was very tired from carrying his burden and gave it to Epimetheus for safe keeping. Pandora wanted desperately to know what was in the box. She waited until Epimetheus was gone. She opened the box, and all of the ills of the world flew out and spread throughout the human world.

The Agricultural Revolution
The shift from the hunter-gather mode of living to an agricultural model provided a more secure supply of food and enabled expansion of the population. However, domesticated animals provided not only food and labor; they also carried diseases that could be transmitted to humans. People also began to rely heavily on one or two crops, so their diets were often lacking in protein, minerals, and vitamins. People began living in larger groups and staying in the same place, so there was more opportunity for transmission of diseases.

Garbage and waste accumulated, and rodents and insect vectors were attracted to human settlements, providing sources of disease. The engraving below shows a woman emptying her bedpan into the street of a medieval village.

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BIO 550 Discussion Early Concepts Of Disease
BIO 550 Discussion Early Concepts Of Disease

The Hippocratic Corpus
For many centuries explanations for disease were based not on science, but on religion, superstition, and myth.

The Hippocratic Corpus was an early attempt to think about diseases, not as punishment from the gods, but as an imbalance of man with the environment. Although it was unsophisticated by today’s standards, it was an important step forward. By considering the possibility that disease was associated with environmental factors or imbalances in diet or personal behaviors, the Corpus also opened up the possibility of intervening to prevent disease or treat it.

The Corpus looked at disease as an imbalance in natural forces or an imbalance in humours (or fluids): melancholy, phlegm, bile, and blood. Health depended on a proper balance of these humours. While crude, this concept of humours provided some sort of rationale for understanding health and disease. Greek physicians prescribed changes in diet or lifestyle and sometimes concocted drugs or performed surgery. An excess of the humour blood, for example, became the rationale for bloodletting, a practice that was followed for centuries (without any evidence of its efficacy).

Despite the contributions of the Corpus, medical and scientific progress in Europe was arrested for several centuries. The population grew, and cities became densely populated, but there was little attention to waste disposal and sanitation. These factors set the stage for endemic disease and periodic epidemics.

The Bubonic Plague (1347-1700s)
Bubonic plague is an acute infectious disease caused by the bacterium Yersinia pestis. The bacteria live in the intestines of fleas and are transmitted to rats by flea bites. The rats, therefore, serve as a natural reservoir for the disease, and fleas are the vectors. Occasionally, an infected flea would jump to a human and introduce the bacteria when a blood meal was taken. The bacteria would then spread to the regional lymph nodes and multiply, causing dark, tender, swollen nodules (buboes), as shown below in a boy a walnut-sized swelling in the inner aspect of his upper thigh. As the infection spread, the victim would experience headache, high fever, delirium, and finally death in about 60% of cases.

Starting in 1347, Europe experienced multiple waves of bubonic plague epidemics that lasted until the late 1700s. It is believed that the bubonic plague originated in Asia and traveled along trade routes into the Black Sea and then into the Mediterranean Sea. From there, it swept through Sicily and Italy and then up through France and the northern European countries all the way up into Scandinavia. There were many subsequent waves of plague that swept through Europe until the late 1700s. The map below shows the spread of plague over a three year period from Asia across the Black Sea into the Mediterranean and then through Italy, France, England, Northern Europe, and into Scandanavia.

Cause of the Plague and Strategies for Prevention
The cause of the plague was not known, but there were many theories. The most popular explanation was that it was caused by “miasmas,” invisible vapors that emanated from swamps or cesspools and floated around in the air, where they could be inhaled. Others thought it was spread by person to person contact, or perhaps by too much sun exposure, or by intentional poisoning. The miasma theory was the most popular, however. One of the popes kept large fires burning at both ends of the room he worked in order to counteract the miasmas. The illustration on the left shows a “plague doctor,” who is covered from head to toe, including a hood, a mask, gloves, and a beak-like sack on his nose. The covering on the nose contained aromatic herbs, which were believed to neutralize miasmas.