Historical- The appearance of plagues played a major role in history and some reasons for why plague started was rats, traveling of boats, and increase in agriculture. In the early centuries, people were living in poor conditions due to overpopulation and that led to them leaving trash all over their streets. The poor living conditions and increase in trash was very unsanitary and rats and fleas began to crowd the dirty streets searching through the trash. The fleas carried diseases with them which they would pass onto the rats and humans. Due to the increase in rats, more and more humans began to catch these diseases that were being passed on from the rats which led to plague. Travel was also a way for diseases to spread because merchants were traveling over boat which carried lots diseases. Similar to the streets, rats were on the boats and would transport the diseases to humans such as the black death. Boats also allowed for the diseases to spread quicker because traveling over boat was faster than traveling on land. Lastly, Agriculture was growing in popularity especially along the Tigris, Euphrates and Nile rivers. Although agriculture allowed for more jobs and crops, it also led to lots of diseases such as Schistosoma. When the rivers would flood the land, the disease would spread among the land and cause humans to get infected with disease because Schistosoma penetrates human skin in the water. Agriculture also led to animal domestication which provided food and resources but the animals also carried diseases with them that they spread to humans. Domesticated animals attracted rats and wild birds that carried disease and animals also were leaving feces all over the land that could lead to diseases

Rats played a major role in spreading infectious diseases

Current Application- Although new technologies have helped prevent lots of diseases they have also led to some diseases. New technology in air conditions led to an outbreak in pneumonia and tampons have been traced to an outbreak involving multiple organ systems. Although air conditioning is a very beneficial technology, it also led to an outbreak of pneumonia in Philadelphia in 1776. Tampons were another invention that caused disease and the newly created Rely tampons were related to an outbreak involving multiple organs. Another new technology that has led to bad health effects are antibiotics. Antibiotics help prevent disease but some bacteria have small pieces of DNA that prevent the resistance of other bacteria which then cause the user to possibly get sick from other diseases. Increase in travel and the ability to travel all or the world in a short amount of time has led to disease spreading faster. Planes allow for people to travel very fast to places all over the world but people could also be infected with diseases and taking them to every place they travel to. Lastly, humans can affect the overall health of a community by not getting vaccines and choosing to not be treated. Measles is a disease that had an outbreak in California in 2015 when people were not getting vaccines for measles and is a good example of human effect on health. This was an example of herd immunity because lots of people were not getting vaccines for measles and the disease could be spread very quickly among the community.

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