A. Key disease carriers, such as insects and rats, thrive in crowded urban settings, further facilitating spread.
B. The unprecedented population densities in fourteenth-century Europe, for example, led to the plague outbreak that claimed the lives of one fourth of the population.
C. Although these infections are easily preventable if adequate water and sanitation are available, the vast majority of the world’s population are lifelong victims.
D. While new global markets have created unprecedented economic opportunities and growth, the health risks of our increasingly interconnected and fast-paced world continue to grow.
E. Pathogens can more readily establish in large populations, since all infectious diseases require a critical number of vulnerable individuals in order to take root and spread.
F. These areas can serve as a perpetual reservoir of disease or disease vectors, placing other parts of the city at risk of an outbreak and allowing the disease to continue evolving, often into a deadlier strain.