Emerging infectious disease
Emerging infectious disease
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Emerging infectious disease

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Emerging infectious disease

An emerging infectious disease (EID) refer to infectious diseases that have either newly appeared in a population or have existed but are rapidly increasing in incidence, geographic range, or severity due to factors such as environmental changes, antimicrobial resistance, and human-animal interactions. The minority that are capable of developing efficient transmission between humans can become major public and global concerns as potential causes of epidemics or pandemics. Their many impacts can be economic and societal, as well as clinical. EIDs have been increasing steadily since at least 1940.

For every decade since 1940, there has been a consistent increase in the number of EID events from wildlife-related zoonosis. Human activity is the primary driver of this increase, with loss of biodiversity a leading mechanism.

Emerging infections account for at least 12% of all human pathogens. EIDs can be caused by newly identified microbes, including novel species or strains of virus (e.g. novel coronaviruses, ebolaviruses, HIV). Some EIDs evolve from a known pathogen, as occurs with new strains of influenza. EIDs may also result from spread of an existing disease to a new population in a different geographic region, as occurs with West Nile fever outbreaks. Some known diseases can also emerge in areas undergoing ecologic transformation (as in the case of Lyme disease). Others can experience a resurgence as a re-emerging infectious disease, like tuberculosis (following drug resistance) or measles. Nosocomial (hospital-acquired) infections, such as methicillin-resistant Staphylococcus aureus are emerging in hospitals, and are extremely problematic in that they are resistant to many antibiotics. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics.

Many EID are zoonotic, deriving from pathogens present in animals, with only occasional cross-species transmission into human populations. For instance, most emergent viruses are zoonotic (whereas other novel viruses may have been circulating in the species without being recognized, as occurred with hepatitis C).

The French doctor Charles Anglada (1809–1878) wrote a book in 1869 on extinct and new diseases. He did not distinguish infectious diseases from others (he uses the terms reactive and affective diseases, to mean diseases with an external or internal cause, more or less meaning diseases with or without an observable external cause). He writes in the introduction:

A widely held opinion among physicians admits the invariability of pathologies. All the illnesses which have existed or which have an outbreak around us are categorized according to arrested and preconceived types, and must enter one way or the other into the frameworks established by the nosologists. History and observation protest wildly against this prejudice, and this is what they teach: Diseases which have disappeared and whose traces are confined to the archives of science, are followed by other diseases, unknown to the contemporary generation, and which come for the first time to assert their rights. In other words, there are extinct and new diseases.

Charles Nicolle, laureate of the Nobel Prize in Physiology or Medicine elaborated the concept of emergence of diseases in his 1930 book Naissance, vie et mort des maladies infectieuses (Birth, Life and Death of Infectious Diseases), and later in Destin des maladies infectieuses (Fate of Infectious Diseases) published in 1933 which served as lecture notes for his teaching of a second year course at the Collège de France. In the introduction of the book he sets out the program of the lectures:

It is this historical existence, this destiny that will be the subject of our talks. I will have to answer, to the extent that our current knowledge allows, questions that you have asked yourself, that every thoughtful or simply curious mind asks: have the infectious diseases that we observe today always existed? Or have some of them appeared in the course of history? Can we assume that new ones will appear? Can we assume that some of these diseases will disappear? Have some of them already disappeared? Finally, what will become of humanity and domestic animals if, as a result of more and more frequent contacts between people, the number of infectious diseases continues to increase?

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