> David Hobby <[EMAIL PROTECTED]> wrote:
<snip>
> Got me, what is the difference between disease
> organisms and parasites? If the individuals are
> sufficiently large, we call them parasites, and if
>they are small enough, we don't?
And Keith wrote (2 different posts pasted in):
>>The most common distinction is that of persistence.
>> Disease is more often acute and is cleared by the
>>immune system. A parasite has figured a way to
>>limit the effectiveness of the immune system and
>>persists for years to a lifetime. Parasites cause
>>persistent disease.
> > There is a reason to use the parasite model....it
> >is a common progression over evolutionary time for
> > a parasite to become a mutualistic symbiote.
> >Disease and parasites are often the same
> > thing, malaria for example.
Delineating one from another is not always
straightforward.
My Steadman's definition of "parasite" is
1) an organism that lives on or in another and draws
its nourishment therefrom
2) the more or less incomplete twin [of fetal
inclusion or conjoined twins] that derives its support
from the more nearly normal autosite
"Symbiosis" is 'any intimate association between two
species; sometimes used as a synonym of mutualism.
Mutualism, commensalism, and parasitism are symbiotic
states.' [not writing the psychiatric definition for
brevity's sake]
"Commensal" is 'an organism which derives benefit from
another, which is unharmed.'
"Mutualism" is 'a symbiotic relationship in which both
species derive benfit.'
Any virus is, by definition, "an obligate
intracellular parasite," but we don't tend to think of
them *as* parasitical (instead of having a cold,
you're parasitized by a rhino- or corona- virus!).
Some disease-causing bacteria blur the lines by being
capable of living free, yet able to parasitize host
cells as well (frex Listeria). Bacteria like
trypanosomes (frex syphilis) can cause years of
illness, yet are not commonly thought of as parasites.
Rickettsia (frex Rocky Mountain Spotted Fever) only
grow inside host cells, yet do not usually cause
long-term illness. And disease can be caused by
'opportunistic' organisms that normally are
commensals, or even mutualists, particularly if the
host is immunologically compromised.
Practically speaking, I think what makes something a
parasite involves the "eeuuww!" factor: tapeworms are
just *gross,* while cold-causing viruses really
aren't.
<raised paw, claws extended, fur fluffed out>
*Cats* are at least commensals, but frequently provide
benefits to the lesser bipedal species as well; if
they cause harm it is *deliberate and predatory,* not
parasitical!
<phphfft!!!>
Debbi
tossing in her mitochondrial cytochromes' worth ;)
(and channeling a large number of domestic felines) ;D
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