An introduction to deep lying pathogens in Chinese medicine
The Su Wen Chapter 3 says:
Spring exposure to wind may cause illness, but if the pathogenic qi remains linked to the body there will then be diarrhoea.[i] Summer exposure to summerheat if it doesn’t cause an immediate illness will lead to malaria-like chills and fevers in autumn. Autumn exposure to damp will lead to cough if it rebels upward, but to withering of the tendons otherwise. Winter exposure to pathogenic cold will certainly manifest as warm [disease] in the Spring.
The Su Wen Chapter 5 says:
Winter injury from cold must certainly emerge as Springtime warm [disease]; Spring injury from wind will produce diarrhoea in the Summer; Summer injury from shu/summerheat must emerge as malaria-like disorder in the Autumn; Autumn injury from damp will produce cough in the Winter.
These quotes were the beginning of the idea that pathogens might remain within the body and only express themselves later.
From the Shang Han Lun up until the Ming dynasty, this was called ‘fu qi’, afterwards they were known as ‘fu xie’; now these names are used inter-changeably. ‘Fu’ means hidden, submerged, lurking. The ‘xie’ means a harmful pathogen produced by unseasonable weather. Qi means about the same but without the emphasis on injury.
When the body is strong, climatic changes do not easily affect it. The Ling Shu chapter 75 describes this well: “Zheng Feng / Normal wind [which is the wind appropriate for the season] only strikes people shallowly, meets [the zheng qi] and then departs. It departs because its qi is weak and unable to overcome the zheng qi of the body”.
When the pathogen is stronger than the zheng qi (normal qi) illness results.But when the pathogen and the body’s zheng qi are equally matched, in some cases the pathogen can enter the body without greatly upsetting the normal balance, only to emerge later when the conditions are right.
This idea comes from long term clinical observation of the course of exogenous diseases. Most invasions will cause wei / protective qi level symptoms first then gradually work their way inwards. Only after moving inside will they exhibit symptoms of intense heat and damage to yin-fluids.
However — contrary to this scenario — some warm diseases seem to start right off with internal heat and yin-damaged symptoms like: fever, headache, thirst, dark urine, red tongue with little coat, deep thready hurried pulse.
Or symptoms of festering internal damp heat such as: malaria-like chills and fever, chest and epigastric discomfort, red tongue, thirst, thick greasy tongue coat and cloudy urine.
The first comes from a pathogen which has been lying deep within Shao Yin (the internal counterpart to Tai Yang), pent up and becoming hot. When it comes out, it often emerges through Tai Yang, hence the typical Tai Yang symptoms of fever and headache.
The latter is a turbid pathogen lying deep at the “mó yuán” around the diaphragm. When it comes out, this type of pathogen often expresses itself through the Yang Ming and Tai Yin channels of the feet – Stomach and Spleen symptoms.
Thus these types of illness, that seem to spring directly from the interior, are called ‘fu xie’, while those that cause surface symptoms first and then work gradually inwards are known as ‘new exposure / xin gan’ or ‘sudden exposure / bao gan’.
The timing of a deep-lying pathogen’s emergence will depend upon constitution, seasonal climatology and the type of pathogen itself. Therefore the timing indications mentioned in the opening quote from chapter 3 of the Su Wen (eg. exposure in winter will lead to warm disease in the Spring) will not always apply, but Spring is mentioned here because of the universal growth of yang qi in that season which tends to encourage growth – in this case, of the pathogen inside. Any other internal buildup of yang qi will also tend to encourage the expression of a deep-lying pathogen.
An underlying infection which the body’s defences cannot eliminate can exist in a precarious balance within the body. Then another factor – which may indeed be an unseasonal change in the weather, but could just as likely be a period of immune-depressing stress – tips the scales and it flares up.
Liu Bao-Yi’s Wen Re Feng Yuan (Encountering the Source of Warm Heat, late Qing) is an in-depth discussion of deep-lying pathogens in warm disease. He traces their theoretical origins in all the early classics, then describes their nature and characteristics, diagnosis and treatment. Although the topic is all ‘warm disease’, Liu (1842-1901) is not an uncritical admirer of Ye Tian-Shi, whose Wen Re Lun, he says, emphasises new invasions of warm disease and ignores the equally important fu qi.
Liu says that the warm disease conditions discussed in the Nei Jing, Nan Jing and Shang Han Lun all are generally deep-lying pathogens …
“but when the Nei Jing says to treat internal wind evil with pungent and cool, and Ye’s Wen Re Lun says a warm disease exposure above first attacks the Lungs, both are pointing to a ‘sudden exposure’ type of warm disease pathogen” which is not deep-lying but a new invasion. He continues:
Deep-lying pathogens express themselves from the depths, and treatment is mainly by cooling and draining internal heat. The symptoms can be varied and complicated, and should be dealt with using the [Shang Han Lun’s] Six Channel system of pattern differentiation, changing treatment method as the progression of the disease demands.
Bao gan / sudden exposure wind warm pathogens specialise in affecting the Lungs, and pungent cooling dispersal is the order of the day. If the heat is intense, also use sweet cold cooling and transforming.[ii]
Nonetheless this condition and a deep-lying condition differ in the routes they take when moving between the surface and interior. The heaviness or lightness of the herbs, and the depth at which they are aimed, also shows the difference in treatment method.
People nowadays all put Ye Tian-Shi on a pedestal, they just shelve the idea of deep-lying pathogens and never mention it. Whenever they run into a warm pathogen, no matter whether it is a sudden exposure or deep lying qi, they simply use Ye’s pungent cooling light and shallow method: Yin Qiao or Sang Ju just flow off their brush. Doctors and patients both go for the easy way, and everyone is happy to do so. There is no one to put forward the theory of deep-lying qi, they even see it as some weird theory. They are utterly at a loss to understand what sort of illness fu qi might be.
What a pity! It is such a common exogenous illness, especially in the South [of China] and not an unusual presentation at all. It is a condition recorded in the Nei Jing, Nan Jing and Shang Han Lun , and thus not some weird theory. In clinic, its incredible that they can’t differentiate it and know absolutely nothing about it – one can hardly bear thinking about the rest of their medical expertise! ” [iii]
[i] Actually a specific type of diarrhoea known as “dong xie” in which as soon as the patient eats they void undigested food.
[ii] Such as Shi Gao (Gypsum) and Gan Cao.
[iii] Humbled and damned by these closing words, I can only remark that all of Liu’s book is a passionate exposition of the theory of fu qi. Liu himself had an outstanding intellect. Taking first place in the imperial examinations of 1865, he resigned his commission at the capital in disgust at the corruption of the late Qing dynasty and took up medicine. He proves his point about the importance of fu qi by his reputation for curing apparently terminal cases using his understanding of deep-lying pathogens. Wen Re Feng Yuan (Encountering the Source of Warm Heat), Liu Bao-Yi, late Qing; Peoples’ Health Publishing, 1982, pp. 60-61.