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Tue Apr 4 13:26:07 EST 1995

Derek Zelmer wrote:

>I think that if you did a survey you would find that most
>parasitologists study symbionts that have a net negative effect
>on their hosts...

Surely this is due to the fact that it is almost impossible to
get funding to study 'commensals' and not due to a lack of interest
or relevence to the field of parasitology?

Personally, I've always viewed commensalism as a benign form of
parasitism in any case. This is in part because the same species can
be a 'commensal' in one host and a 'parasite' in a different host
(Zelmer definitions). An infection may also start out as 'commensal'
but due to environmental or other factors become 'parasitic'. Is it
worth having two rigid terms to describe what may be transient
conditions? I don't want to get back into a discussion of virulence
again, however....

Part of the problem here is historical in nature. The term parasite
is almost never applied to infectious bacteria or viruses, yet by the
definitions being used in this thread they could just as easily be
considered parasites as the eukaryotes that are traditionally the
subjects of parasitology texts. Perhaps the definition of a parasite
should be: a eukaryote living in or on another eukaryote on which it
is dependent and from which it derives nutritional benefits. Unless
you WANT to include bacteria and viruses of course.

In any case, what matters is that, whether you call them rutabagas,
yellow turnips or neeps, almost all of us recognize a parasite when
we see one. My list of commensals/parasites would probably be very
similar to Derek's ecto-/endo-symbionts.

C. Graham Clark, Ph.D.
Laboratory of Parasitic Diseases,
National Institutes of Health,
Bethesda, MD 20892-0425

Ph.: 301-496-4740
FAX: 301-402-4941
e-mail: cge at cu.nih.gov

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