morphostasis.org.uk

A proliferation of pathogens through the 20th century

Published In the August 2008 edition of the Scandinavian Journal of Immunology.)

It points out that the meaning of "pathogen" has shifted over the last 120-130 years.

Additional notes:

It should be an inescapable conclusion that the meaning of "pathogen" is still in transition. Its original meaning was "a specific causative agent of disease". Many people now define it as a "causative agent of disease - especially a bacterium or a virus" or something along those lines. However, there is a greater transition towards it becoming a synonym and replacement for a "pathogenic organism": this is now well under way - particularly in its extensive use in the bio-medical literature. Some dictionaries already define a pathogen as "a disease causing organism". I believe that there is an imperative to consider whether this drift should be allowed to continue and how far this drift should be allowed to proceed. In the published article I suggested, "Perhaps the prevailing theories of self/non-self-discrimination and of immune system function were fully compatible with this interpretation of pathogen - anomalies and anachronisms are only now coming into focus." This may be better expressed as "Perhaps the prevailing theories of self-/non-self-discrimination and of immune system function failed to highlight the anomalies and anachronisms that would have arrested this drift: they are only now coming into focus."

This challenge could be summed up in this pertinent question: "Is asbestos a pathogen? (or more precisely, does an asbestos fibre qualify as a pathogen when it causes disease?)"  I believe you ought to answer yes; and this response straightaway exposes the general misuse of this term.

The term pathogenic bacterium may seem to be more or less the same as a bacterial pathogen. But these is a clear difference in emphasis. In the first it the bacterium that is the principal property; this has the expected properties of a bacterium with the additional property of being able to cause damage. In the second, it is the pathogen that is the principal property; this has the "expected" properties of a pathogen with the additional property of also being a bacterium. To me, it seems that there is far more emphasis on - and scope for - a variety of pathogenic mechanisms in the first than in the second. So, in addition to advocating a return of pathogen to mean any agent that causes disease or damage, I suggest that we should use pathogenic organism rather than an organismal pathogen (where organism is the generic proxy for bacterium, virus, fungus etc) unless there is a compelling reason to emphasise the second.

The article ends by suggesting that an alternative shorthand might be called for to replace pathogen where we really mean a pathogenic (micro-)organism.

Pathogerm could prove to be an appropriate substitute; this name is both "twee" and rather colloquial. Both these properties would act as appropriate reminders that this is nothing other than a convenient abbreviation that hides a wealth of deeper properties. It has the advantage of sounding similar to pathogen but remaining clearly distinct.

The perspective persists that aggressive adaptive immune responses are caused by the interaction of TLRs (toll like receptors - expressed on dendritic cells) with PAMPs (pathogen associated molecular patterns). However, as highlighted, PAMPs should really be regarded as MAMPs (microbe associated molecular patterns). Since several million different bacterial species are non-pathogenic to man and only about 50 are regularly pathogenic, why do we not become awash with aggressive adaptive immune responses to these non-pathogenic species (particularly the 500 or so different commensal species that live within and upon our bodies)? There is something not consistent and quite illogical here. Oral and gut bacteria are both encouraged to inhabit us and they are useful to us and play a protective role. If their MAMPs were to regularly provoke the adaptive immune system into an aggressive response, the outcome could be a devastating inflammation of our mouths and gut (it looks as though Crohn's disease, ulcerative colitis and the mouth ulcers of Behcet's syndrome may be unwelcome examples of such misdirected aggressive immune responses). This should indicate to us that these aggressive responses are channelled away from aggression when the encounter is with non-pathogenic, commensal or symbiotic organisms - which seem to be welcomed and encouraged into colonising our mouths and gut.

At the beginning of this article I have used the quotation "The repetition of a catchword can hold analysis in fetters for fifty years and more." (Benjamin N. Cardozo, 1870-1938). However, Francis Bacon (1561-1626: he is, perhaps, the father of "natural philosophy" - now commonly called "science") - also has much to say on this in his comments on "Idols of the Mind" in Novum Organum (copy here, see sections XLIII and LIX):-

XLIII "There are also idols formed by the intercourse and association of men with each other, which I call Idols of the Market-place, on account of the commerce and consort of men there. For it is by discourse that men associate; and words are imposed according to the apprehension of the vulgar. And therefore the ill and unfit choice of words wonderfully obstructs the understanding. Nor do the definitions or explanations wherewith in some things learned men are wont to guard and defend themselves, by any means set the matter right. But words plainly force and overrule the understanding, and throw all into confusion, and lead men away into numberless empty controversies and idle fancies."

LIX "But the Idols of the Market Place are the most troublesome of all — idols which have crept into the understanding through the alliances of words and names. For men believe that their reason governs words; but it is also true that words react on the understanding; and this it is that has rendered philosophy and the sciences sophistical and inactive. Now words, being commonly framed and applied according to the capacity of the vulgar, follow those lines of division which are most obvious to the vulgar understanding. And whenever an understanding of greater acuteness or a more diligent observation would alter those lines to suit the true divisions of nature, words stand in the way and resist the change. Whence it comes to pass that the high and formal discussions of learned men end oftentimes in disputes about words and names; with which (according to the use and wisdom of the mathematicians) it would be more prudent to begin, and so by means of definitions reduce them to order. Yet even definitions cannot cure this evil in dealing with natural and material things, since the definitions themselves consist of words, and those words beget others. So that it is necessary to recur to individual instances, and those in due series and order, as I shall say presently when I come to the method and scheme for the formation of notions and axioms."

Pathogenic probably came to us via the French from their pathogenique. They also use the term pathogene (both as a noun and as an adjective according to some dictionaries). They have been much more faithful to its original meaning as the following definitions (of pathogene) demonstrate:

I received these helpful comments from Jeff Aronson ("When I use a word .. " series in the BMJ/QJM) in response to my contact:

"The datings may need revision. The following are the dates of the earliest examples given in the OED:
Pathogenetic 1930
Pathogeny (= pathogenesis) 1842
Pathogenic 1850
Pathogenesis 1850
Pathogenesy 1851
Pathogenous 1853
Pathogen 1880

This and your bibliometric data seem to argue that pathogen is a back-formation from (say) pathogenetic. However:
(a) The earliest datings in the dictionaries are not necessarily the earliest instances; antedatings are constantly being discovered;
(b) the word "pathogen" exists in other languages. The earliest uses in German and French, at least, long antedate even "pathogenetic". For example, there are numerous instances of "Pathogen" in German in the 18th century (see Google books). An exploration of German texts might give a different result.

The earliest citation of "pathogen" in OED establishes that the micro-organism meaning was already there in 1880: 1880 Libr. Universal Knowl. VI. 647 Pathogen [the micrococcus of] contagion. I am not sure if the definition that you cite under the heading of Merriam Webster from 1880 is actually from that date, but if it is, that also suggests that the restriction in meaning to organisms was not particularly insidious. There seems to be no earlier use of the word to mean anything other than that."

My search for the first use of "pathogen" was gleaned largely from Nature and Science - these being the only sources that I could access. I have made an assumption that these journals typified general use but maybe that is not so. Whatever, there are two points worth making: first, Metchnikoff avoided this term - perhaps deliberately; second, the recent discovery and interest in microbial disease (the era of Koch and Pasteur) seems to have carried with it an early supposition that most disease would turn out to have an infective origin.
 

Thanks are due to Alan Orme for pointing me in the direction of reference [4] "The Unfolding of Language" by G. Deutscher.