Although it is important to understand development stages and disease patterns within individual nations, it is equally important to understand that diseases respect no national borders. Because of globalization, diseases and disease-causing conditions spread rapidly from less to more developed nations and vice versa. For example, air pollution from China is now causing heart disease and asthma in the western United States, and the recycling of used U.S. electronics equipment across Asia is releasing toxic acids and metals into drinking water in those countries.
Because the United States and Mexico share the same water, air, and, to a growing extent, economies where the two nations meet, U.S. citizens need to be especially concerned about health conditions in Mexico. For example, the many factories located in Juarez, a large city just south of El Paso, Texas, are notorious for spewing toxic chemicals into the air and aquifers shared by both countries. Similarly, only one-third of the sewage gen- erated by residents of Juarez is appropriately treated. As a result, human wastes drain from Juarez into the Rio Grande, and from there into El Paso’s drinking water supplies, making gastrointestinal disease a leading cause of infant mortality in both cities. As this example suggests, those who live in the more de- veloped nations have a vested interest in understanding health and illness in the less developed nations.