This was a very vague question, but I belive the word you are looking for is "Plague"
epidemic
in the butt
An epidemic is the rapid spread of a disease to a large number of people within a specific population or region. Epidemics can vary in scale and severity, and often require public health interventions to control and prevent further spread of the disease.
people got sick,had over cramped space areas, which caused to spread disease and fires. Those are some of the resolutions of rapid growth in cities
Rapid population could result to food and water shortages and could also increase the percentage of people who would be infected by an infectious disease. Spread of disease is due to overcrowding that could increase the possibility of carrying a virus or bacteria.
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Rapid detection of disease exposure is important for several reasons. For many diseases, detecting the infection and beginning treatment early may reduce the severity of the symptoms or even prevent the disease completely. Rapid detection of disease exposure is also important to prevent further spread of the disease.
the rapid spread of disease through crowded cabins
The disease that spread through the trade routes of the Gobi Desert to Europe was the bubonic plague, often referred to as the Black Death. This pandemic, which began in the 14th century, was transmitted via fleas that infested rats aboard trading ships and caravans. It had devastating effects on the population of Europe, killing an estimated one-third of its inhabitants. The interconnectedness of trade routes facilitated the rapid spread of this deadly disease across continents.
The standard definitions is "(of a disease or disease-causing organism) likely to be transmitted to people, organisms, etc., through the environment."It has come to mean " likely to spread or influence others in a rapid manner."
plague
What Bubonic plague caused an rapid spreading disease