another defini post

Charles T. Faulkner ctfaulkn at UTKVX.UTCC.UTK.EDU
Fri Mar 31 15:51:53 EST 1995



On Fri, 31 Mar 1995, derek a. zelmer wrote:

> On Thu, 30 Mar 1995 ctfaulkn at UTKVX.UTCC.UTK.EDU wrote:
> 
> > 	In an earlier post I commented on the sometimes "fine-line"
> > between being a commensal and a "parasite (pathogen)".  I think Jeff's
> 
> 	I am not sure that it is a fine line, it seems more like a large 
> grey area to me. 

	I agree. A large grey area is probably the appropriate description
	for this distinction.  

>You cannot differentiate between parasitism and 
> commensalism based solely on metabolic dependence, you must look at the 
> overall effect on the host. 

	Ok. What measurment scales should be used?  Clearly, there are 
problems with using pathogenicity (morbidity) because in some cases the net 
negative effect is so negligable that it rarely, if ever, results in 
clinical disease. However, host factors can change over time so that a once
benign parasite..... now becomes an agent of excess morbidity, and perhaps
mortality.  Or conversly, as Ewald noted, pathogenic parasites become benign.

> If there is no benefit to having the 
> endosymbiont it is definitely a parasite because it is definitely causing 
> a negative effect. 

	So if the endosymbiotic relationship is anything but mutualistic a 
commensal would technically be engaged in a parasitic relationship with 
its host, because ....

> It is taking up nutrients that must be supplied by the 
> host, it is causing an immune response which requires energy, and is 
> likely to have an effect on other bodily functions.
> 
	So if we develope a test for anti-E.coli IgA, this would imply 
that it is a parasite, rather than a commensal because we have 
demonstrated an immune response ?  

	I guess I still see metabolic dependency as the important criteria
because I think we can get an immunologic response from living and nonliving
pertubations to the host.  I believe the questions still goes back to 
measurement scale for describing net effect on host. Pathogenicity is a crude
meassure.... nutrient robbing (metabolic dependence) no matter how small 
seems more appropriate.

**********************************
*      Charles T. Faulkner       *   When you don't know where you're
*  Univ of Tennessee, Knoxville  *   going any road will take you there.
*   (ctfaulkn at utkvx.utk.edu)     *                            Alice
*********************************                                
 



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