There are "three theories" about epidemic diseases in TCM.

"Qi" is the core of Chinese medicine in understanding natural diseases and human diseases, and the occurrence of plague is also discussed from this.

Chinese medicine has a long history in treating epidemic diseases. Traditional medicine believes that the occurrence of plague is mostly related to "qi", and "qi" is the core of Chinese medicine in understanding natural and human diseases. Generally speaking, ancient physicians had three views on the epidemic source: one was "seasonal qi", the other was "violent qi" and the third was "miasma".

Wang Shuhe, a doctor in the Western Jin Dynasty, and others hold the view that the abnormal change of climate, that is, the untimely gas, will lead to the occurrence of epidemic diseases. In Treatise on Febrile Diseases and Cases of Typhoid Febrile Diseases, he pointed out: "All travelers should be warm in spring to resist severe cold, hot in summer to resist severe cold, cold in autumn to resist intense heat, and cold in winter. This is not the case, but it is true for people over one year old who have similar diseases. " This means that abnormal and drastic climate change is an important factor that causes people to suffer from epidemics. So, how to judge "untimely gas"? Ancient doctors often choose a solar term, observe and compare the climate at this time with the climate that this solar term should have, so as to judge whether it belongs to "untimely gas". For example, Wang Shuhe observes the climate of the four seasons on the day of the twenty-four solar terms, and judges the arrival time of normal climate according to the temperature difference between cold, hot and cold of the four seasons. If the time before and after exceeds a certain range, it is considered abnormal and may lead to the occurrence of the epidemic. In his view, the normal climate is warm in spring, hot in summer, cool in autumn and cold in winter, and "not getting angry" is the condition for the occurrence of epidemic diseases. Specifically, in the normal season, there are at most three solar terms. If there is "non-seasonal warmth in winter" or "from vernal equinox to autumnal equinox, there is sudden cold in the sky" (cold is hot and hot is cold), it is "untimely gas" that has caused the epidemic.

The representative physician who holds the theory of "hostility" is Wu Youke in the late Ming and early Qing Dynasties. In Treatise on Epidemic Febrile Diseases, Wu Youke creatively proposed that the cause of plague was not wind, cold, summer heat and dampness, but "a strange feeling between heaven and earth", which he also called "strange gas", "furuncle gas" and "miscellaneous gas". Wu Youke founded a new theory of plague etiology-the theory of rage, which holds that plague is different from typhoid fever and cold, and also different from "seasonal diseases" caused by improper seasons. Seasonal diseases will not form an epidemic, but plague will cause an epidemic, that is, the so-called "closed door, regardless of size, similar symptoms." Epidemic pathogens are not common exogenous pathogens such as wind, cold, heat, dampness, dryness and fire, but "a strange gas between heaven and earth", which is characterized by being invisible, inaudible and intangible. As mentioned above, Wu Can also pointed out that plague is a widespread and infectious disease caused by a special kind of boils. Men and women, old and young, physical strength, once exposed, may get sick. Wu Youke's "furuncle-qi theory" broke through the old theory of thousands of years, which is basically consistent with the understanding of pathogen characteristics in modern epidemiology.

People who hold miasma theory believe that some epidemics are caused by miasma infection in specific areas, also known as miasma. Miasma, also called miasma poison, was originally called miasma because the northerners in China did not adapt to the local damp-heat and steaming depression when they arrived in Lingnan, and did not understand the specific causes at that time. For example, in The True Story of Medicine in Ming Dynasty, Yu Juan once said: "The miasma in Lingnan, Fujian and Guangzhou refers to the fog and dew in Shan Lan. Some doctors believe that miasma can be divided into broad sense and narrow sense. In a narrow sense, it refers to malaria, and in a broad sense, it refers to some diseases that occur in a specific area and are closely related to the climate in this area. For example, in the Ming Dynasty, Wu mentioned in the Outline of Jiyang that "mortals are infected with rime and snake gas, and their symptoms are aversion to cold, fear of cold, headache and endless rest. "It can be seen that the occurrence and prevalence of this epidemic has certain regionality and has a great relationship with the local climate and environment. ▲