Why did the population migrate?

Natural disasters often cause large-scale population migration. During the Tangshan earthquake, the wounded were directly transported to Chengdu and Chongqing in the southwest hinterland of China. During the period of urban reconstruction, people evacuated in the form of relatives and friends almost spread all over China. Nowadays, under the current economic conditions, going out to engage in labor activities has almost become the most important form of self-help activities for residents in disaster areas.

The large-scale migration of plague population first created conditions for the spread of some endemic diseases and made some diseases popular. For example, the Black Death in the Middle Ages, the latest epidemic in the history of China and Yunnan, all started with population mobility.

Population mobility has caused two problems. First, when the population in the disaster area flows out, it may spread the endemic diseases in the disaster area to the unaffected areas. More importantly, when the disaster area begins to rebuild and the population returns home one after another, endemic diseases and infectious diseases will be brought back to the disaster area. If the disaster area has the conditions for epidemic diseases, it may create new epidemic areas.

The second major problem brought by population mobility is that it interferes with the immune status of some people who mainly rely on immunity to control diseases, resulting in local non-immune people, thus creating conditions for the prevalence of these diseases.