Plagues originate from various contributing factors. The most prominent being the shift from a hunter-gatherer lifestyle to a stationary, sedentary lifestyle. The conversion from migrating to farming facilitated both positive and negative consequences. As hunter-gatherers, roaming, searching, and moving was expected. By following animals as their source of food, bearing children was considered less than ideal. The ongoing pace made the process difficult, however, they did reap several benefits. Constantly being on the move resulted in small population groups, reducing human-to-human transmission, in addition to, limited exposure to parasites (commonly associated with rotting food and feces). As hunter-gatherers, infections were unavoidable; fleas adapted, and wild animals were the reservoirs for various diseases (i.e. malaria, relapsing fever, yellow fever, etc.). Yet, due to the spaced-out, small population, illnesses typically made isolated appearances and seldom affected the group in its entirety (CANVAS slides).

Once the agricultural revolution and domestication of animals were set, other major factors such as the scientific-industrial revolution and tool making steadily affected the growth of the population. This development led to a sedentary lifestyle – cultivating modern foods and attracting animals for further domestication. Soon, food production became the backbone for the people, enticing the population to stay in one place. Animal domestication brought out many benefits, including, food, clothing, transport etc. However, as populations grew, and the accumulations of pathogens increased, the spread of infections began to run rapid. In the past, separation and isolation aided the prevention of disease. Now, the squalid conditions and proximity of animals harbored various vectors of infectious diseases (CANVAS slides).

The human diet was deteriorating, and many were developing nutritional deficiencies (i.e. iron deficiency, anemia) due to their concentrated efforts in growing and eating single crops. Lack of nutrition increased their vulnerability to infections and diseases began to arise from concentrated areas. Diseases (i.e. smallpox, influenza, malaria, etc.) from animals evolved and adapted to humans. Human transmission or ‘crowd’ diseases went rampant in dense populations as contamination/pollution by food and water became prominent.

Today, other factors such as globalization, climate change, human health changes, and societal issues, are key in the diffusion of disease. For example, in China, the modeling of medium-scenario warming indicates that the transmission zone of freshwater snail–mediated schistosomiasis will extend northward, putting another 20 million people at risk by 2050 (McMichael). Additionally, diverse health risks are also posed by the deprivation, displacement, and conflict from shortages of fresh water. In many populations, such as Bangladesh, Vietnam, Egypt, and Iraq, river flows are threatened by the loss of glacier mass and snowpack due to global warming and increased diversion of flow by neighbors upstream (McMichael).

Numerous factors play a role in the diffusion of disease. In order to mitigate the risk of a pandemic disease, it is vital for us to be aware and conscious about our actions. Proper sanitation, abiding by standards, and being informed on global (large-scale) impacts and changes, are just several of the actions that we can do to minimize the distribution of disease. Though we do not have control on the evolution of viruses and bacteria, as people, we can make considerable impact on overall health if we are aware and make attempts to aid the situation.