The microbiome has become one of the major determinants of health [1]. We have recently proposed that the equilibrium of Man in Nature could be recognized as a determining factor in defining health (not only human but certainly beyond all animal species) [2]. As a consequence, could a qualitative/quantitative evaluation of the microbiome constitute an exclusive marker of health, ignoring WHO's (now old) definition?
The role and consequences of the microbiome are superimposed, without one being able to disentangle one from the other. Is the disease related to an imbalance of the microbiome, or are the abnormalities of the microbiome favored by any pathology? Maybe both, but the precise mechanism is still unknown. One can only observe the existence of a vicious circle of self-maintenance disequilibrium/disease both on the infectious levels and on autoimmunity.
Previous studies show that microbiome (gut, skin, vagina) in healthy individuals is associated with its strong variety: “we found the diversity and abundance of each habitat's signature microbes to vary widely even among healthy subjects, with strong niche specialization both within and among individuals” [3]. These authors have shown that most variation in the human microbiome is not well explained by these phenotypic metadata: “Other potentially important factors such as short- and long-term diet, daily cycles, founder effects such as mode of delivery, and host genetics should be considered in future analyses” [3].
Other studies show the possibility of reconstitution of microbiome imbalances in the appearance of infectious processes [4]. The juxtaposition of metagenomic results, both chronologically and geographically, but also the comparison of taxa distributions with pathological and environmental data, allows us to better understand their evolutionary processes [5].
Would the possibility of adaptation of the microbiome to its environment be a characteristic element (maybe the only characteristic, at the microbiological scale) of health? In other words, a functional lacking, an increased competitiveness between bacterial/viral/mycotic species or a loss of mutualistic interactions would all be markers of a present or future disease, at least a factor favoring the development of a pathology. To paraphrase the French poet Boileau, “illness was born one day of uniformity”…
So, can health only be defined by an equilibrated microbiome? Reasonably no, this heading question is only a provocation (even if microbiome-focused therapies are in current development [6], and even if the link between microbiome perturbation as an emerging risk factor for cardiovascular and cerebrovascular disease has recently been pointed out) [7]. Microbiome analysis if absolutely fascinating and of high interest for the interaction host-environment, but we do not have to ask too much to microbiome. Health cannot be only related to it, as a pierre angulaire or the Holy Grail.
While for almost two years a global pandemic has affected almost the entire world population (COVID-19), has forced us to change all of our social, eating and behavioral habits, will our health remain the same? The prolonged wearing of the mask will he have consequences (lasting? reversible?) On our facial skin microbiome (with the development, in particular of what is called “maskne”) [8], oral, nasal (and overall respiratory)? The use of hydroalcoholic gel in profusion will it modify in a prolonged way our skin microbiome at the level of our hands? We still do not know the long-term consequences of these changes on our health and on the definition of it which remains to be asked.
Disclosure of interest
The author declares that he has no competing interest.
References
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