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1. part of medical science that studies the causes of diseases and dysfunctions | the very cause of a disease: disease a etiology unknown
2. in Greek and Roman culture, the study of the origins of cities, traditions and sim. | explanation of natural facts by myths
3. (extens.) investigation into the causes of a phenomenon, of a process: the etiology of a conflict | in ethnology, narration aimed at explaining the meaning of a natural fact, of an institution, of a rite.
Historically, starting from the classical tradition and up to the Renaissance it was believed that the disease was caused by the imbalance of the four humors: black bile, yellow bile, blood and phlegm alternatively, diseases were attributed to "malefic miasmas" (the term malaria suggests that the unhealthy air of the swamps causes malarial fevers), or to witchcraft or curses, if not divine punishment.
The first to suggest a natural cause for a disease was Leoniceno, who in 1497 published the De epidemia quam morbum gallicum vocant, in which he addressed the problem of the etiology of syphilis.
For a long time in the history of medicine it was debated whether the cause of a disease lay in a single factor, or whether it was the joint result of multiple factors acting synergistically.
In the 19th century, these two points of view saw Pasteur and Bernard as their champions, in a heated scientific contest.
Bernard studied environmental factors, external and internal, defending the idea that the disease originated from the loss of the organism's balance (homeostasis), generally due to the concurrence of a large number of factors.
Pasteur was the first to demonstrate the correlation between bacterial infection and certain diseases, focusing his efforts on the search for a microbial agent when a new pathology appears.
The contest was therefore won by Pasteur and his followers, and as a result the microbiological theory was quickly accepted and spread among doctors.
The concept of "scientific etiology" was formulated by Robert Koch, who postulated a set of criteria to prove without doubt whether a given microbe caused a specific disease.
Only after the mid-twentieth century did the idea spread that, as Bernard argued, the cause of disease can lie in the interactions between several elements.
We therefore speak of "multifactorial etiology of a disease" when the causes of the disease are represented by the concurrence of several factors of different nature, which apparently are not in direct connection with each other. This circumstance is extremely frequent. Diseases of the vascular system such as arterial hypertension, psychiatric diseases, rheumatological diseases, diabetes, some neurological diseases, and many diseases of various other organs and systems are generally multifactorial.
More rarely, a single etiological factor is sufficient to explain the entire symptomatology, such as in the case of infectious diseases (as already demonstrated by Pasteur), genetic diseases, or intoxications.
understand the difficulties encountered in defining "epidemiology"
learn the five key words that characterize the discipline
Now is the time to answer the classic question that arises when facing a new discipline with a not very explanatory name:
From the etymological point of view, epidemiology is a composite word (epi-demio-logia) of Greek origin, which literally means "speech about the population»
The study of diseases can take place in 4 different contexts or dimensions: (1) the molecular dimension, used by molecular biology, biochemistry and immunology (2) the tissue (i.e. the tissues) and organic (i.e. the organs) dimension, used by pathological anatomy (3) the size of the single individual, used by clinical medicine (4) the size of the population, which is that used by epidemiology.
Obviously these study dimensions must not be seen as disjoint and separate from each other, on the contrary, they are strongly complementary: in fact, a thorough understanding of a disease can only be obtained by adopting an integrated approach of the four aforementioned dimensions.
To say more exactly what epidemiology is is not an easy task, indirect proof of it is the existence of many definitions.
The fact is that epidemiology, more than an autonomous and independent body of knowledge, is a methodology, a technique for approaching problems, a "philosophy". Epidemiology is a "different" way to study health and disease, and it is a transversal science, in that, overlapping with many other disciplines, it helps them to draw conclusions from the facts.
Here are some definitions of epidemiology proposed by distinguished scientists:
In the three definitions explicit reference is made to man or to human medicine however, as already mentioned, epidemiology is a study methodology, and therefore there are no substantial differences between medical epidemiology and veterinary epidemiology, if not those related to the subject of study. : the man in one case, the animal in the other.
It must be admitted that the three definitions now provided are complete and authoritative, but certainly not completely understandable for those approaching the subject for the first time.
There is another simpler definition and therefore more suitable for educational purposes:
The fact that diseases are studied not in the single individual but collectively, that is, at the population level, it must not suggest that epidemiology deals only with infectious or contagious diseases, which typically (but not always!) involve many individuals in a population (but almost never all). In fact, epidemiology deals with ALL diseases but, unlike other disciplines, it deals with them exclusively at the population level rather than as an individual. This concept will be expanded and become clearer later. Already, however, it is good to remember that, in epidemiology, the disease in the SINGLE animal has no meaning. The individual is only important as part of a community.
There are five keywords in the definition:
They will be considered in more detail in the next unit.
IN THE NEXT UNIT:
the meaning of each of the 5 key words that enter one of the definitions of "epidemiology" is explained in more detail.