Need layman explanation

PMacklon macklon at acs.ucalgary.ca
Mon Sep 12 12:21:15 EST 1994


In article <34spsn$aa6 at news.tamu.edu>, muttiah at tamu.edu (Ranjan Muttiah)
wrote:

> I need a layman's explanation of why fungi often attack
> the surface of an organism (plants or animals both seem
> afflicted the same way) say compared to bacteria that
> attack organs deep in the body and the surface of the body.

My answer is freely borrowed from the introductory chapter of "Medical
Mycology - The Pathogenic Fungi and The Pathogenic Actinomycetes", by J.W.
Rippon, and published by the W.B. Saunders Company.  Apologies to the
author:

Most fungi, with the exception of a few dermatophytes, are not dependant on
pathogenicity to ensure the propagation of the species.  Fungi that can
cause disease do so due to some special metabolic trait that allows
survival inside the body under what are, especially for the fungi, adverse
conditions - elevated temp., reduced redox, and host defences.  Diseases
such as histoplasmosis, blastomycosis and cocidiodomycosis are blind alleys
- they are not generally of use in disseminating the species due to
contagion.  To cause infection the fungi undergo drastic metabolic and
morphologic changes.

Another reason why is because the most common infectious fungi seen are the
dermatophytes.  These organisms utilize keratin (dead skin, hair) and some
depend on human or fomite contact for transmission; no longer having
significant soil reservoirs.  Dermatophytes do not invade living tissue -
only dead "tissues" such as outer skin layers, hair, nails, fur, feathers. 
The disease is mostly a toxic and allergic reaction to the presence of the
organism and its metabolic by-products.  These fungi often prefer cooler
temperatures for growth.

Trust this helps.

Peter



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