Nosology and why diseases expanded around the world

(diseases spread as mankind congregated into a squalor of cities)

Cities have inspired a dismal narration of decay and misfortune

From Petronius to Dickens and Zola, writers have seen the metropolis as a warren of corruption, poverty, violence, and disease. The very existence of cities seems to bring fear that the hubris of creating them will be punished by disaster and collapse.

  • They evoke images of the swamp and the jungle.
  • From their beginnings until the twentieth century, cities have been pestholes.
  • In fact, only when towns became big cities did massive die-offs become a regular part of human life.
  • When farmers and villagers started to crowd into cities, this immunologically virgin mass offered a feast to germs lurking in domesticated animals, wastes, filth, and scavengers.
  • Countless people were sickened and killed by previously unknown epidemics: smallpox, measles, mumps, influenza, scarlet fever, typhus, bubonic plague, syphilis, gonorrhea, and the common cold.
  • Many of these diseases attacked with a savagery they rarely show today, demoralizing entire societies.
  • If we are to see why new epidemics are again striking an increasingly urbanized world, we must understand why plagues and cities have always developed together.
  • Farms and villages started to increase the incidents of death after the nomadic movements of humans

  • For several million years, the main causes of nomadic human deaths were accidents and wounds.
  • Permanent farms and villages made death by disease far more frequent.
  • Then the population explosion of the Bronze age, 6,000 years ago, took city dwellers beyond a crucial threshold.
  • Urban masses became sufficiently large and dense to support zymotics, or crowd diseases, what in other species are called herd diseases.
  • For the first time, infection became humanity's chief cause of death.
  • Despite a few respites, this would remain true in the West until this century.
  • Infections are still the main killers in many poor nations, and they recurrently threaten the rich ones.
  • The reason epedemics did not take hold until urban times is simply the conditions imposed by the grouping of numbers of people.
  • While nomads were not free of infection, their most common diseases were chronic, not acute.
  • Deadly epidemics remained relatively limited and infrequent for the same reasons they had been so among hunger-gatherers.
  • People did not live densely packed together which facilitates the transmission of germs from one person to another.
  • Their settlements were sufficiently far apart, and travel was sufficiently limited, to keep outbreaks of diseases localized.
  • Writers often speak of crowd diseases with the metaphor of fire and of human hosts as fuel

  • If there is too little fuel or if it is too thinly scattered, the blaze sputters out.
  • The image, though simplistic, is basically accurate.
  • In epidemiologists' terms, a zymotic persists only if the population is dense enough to keep transmitting the germs and big enough to keep producing new susceptibles.
  • Herd diseases jump from animals to humans and thrive only if the people form a superherd.
  • Once cities hold several thousand people, they can support most present-day crowd diseases.

Pointing to a unit about disease and sickness. Unit about diseases and sickness at noso-, -nosis.