Patocenosis

Pathocenosis: A Holistic Approach to Disease Ecology

Abstract: The History of medicine describes the emergence and recognition of infectious diseases, and human attempts to stem them. It also throws light on the role of changing environmental conditions on disease emergence/re-emergence, establishment and, sometimes, disappearance. However, the dynamics of infectious diseases is alsoinfluenced by the relationships between the community of interacting infectious agents present at a given time in a given territory, a concept that Mirko Grmek, an historian of medicine, conceptualized with the word ‘‘pathocenosis’’. The spatial and temporal evolution of diseases, when observed at the appropriate scales, illustrates how a change in the pathocenosis, whether of ‘‘natural’’ or anthropicorigin, can lead to the emergence and spread of diseases.

Keywords: pathocenosis, emergence, infectious diseases

INTRODUCTION
The history of medicine gives the epidemiology of infectious diseases a unique perspective in time and space, highlighting possible relationships between different diseases occurring in particular economic and social contexts.
In 1933, Charles Nicolle proposed a dynamicconcept of the ‘‘birth, life and death of infectious diseases’’ to highlight the continuity and dynamics of what we could call the pathogenic domain of a given host population, i.e., the disease combinations observed at a given time (Nicolle, 1933). This approach focuses on the processes of disease development and succession at the scale of the host population.
Charles Nicolle (1919 in Blancand Baltazard, 1944) also proposed the pioneering concept of ‘‘asymptomatic infection,’’ crucial for understanding the suddenappearance (i.e., emergence) of certain diseases through clinical signs in particular circumstances.
In 1969, Mirko Grmek proposed considering diseases of a given host population as a whole, including their historical and geographic dimensions. By analogy with ‘‘biocenosis,’’which is the ecological concept of all living organisms that coexist and interact within a defined territory, Grmek defined pathocenosis as follows: ‘‘by pathocenosis, I mean the qualitatively and quantitatively defined group ofpathological states present in a given population at a given time. The frequency and the distribution of each disease depend not only on endogenous—infectivity, virulence,route of infection, vector—and ecological factors—climate, urbanization, promiscuity—but also on frequency and distribution of all the other diseases within the same population’’ (Grmek, 1969). Thus, for the first time in the history of medicine—beyond a nosological framework that encloses diseases in a frozen disciplinary framework (e.g., respiratory diseases, arboviral diseases, sexuallytransmitted diseases)—Grmek offered a temporal and spatial approach to understand the dynamics of infectious diseases and their interdependency. Grmek (1969, 1997) saw the health state of a population as a complex dynamic phenomenon leading to a wide range of epidemiological patterns subject to environmental and human factors. Based on this concept of ‘‘pathocenosis,’’ Grmek examined the historicalprogression of diseases across Europe during the past two millennia: over time, plague succeeded leprosy and was successively followed by syphilis, smallpox, cholera, tuberculosis, and, most recently, the acquired immune deficiency syndrome (AIDS). Even if such a succession can be coincidental, or if appearance and disappearance of successive diseases may have the same causes, these observations raisethe question of interactive causalities.
Following Mirko Grmek, we propose to revisit some changes in pathocenosis in the light of the complex and dynamic processes in which the infectious agents potentially interact, keeping in mind the importance of the ‘‘asymptomatic infections’’ highlighted by Charles Nicolle.

CONCEPT OF PATHOCENOSIS IN THE LIGHT OF THE HISTORY OF PLAGUE IN EUROPE...