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Why do many parasites affect the liver?

Stephen G. Kayes kayes at SUNGCG.USOUTHAL.EDU
Fri Sep 15 19:24:57 EST 1995

Evening all:

	If Graham took exception to my statement I will defer to his 
expertise in as much as I have not had anything to do with E.h. since 
graduate School some 20+ years ago. 

	However, according to the text by Markel and Voege (1981) p.26 
they say that most cases of E.h. are asymptomatic and the organisms live 
happily in the colon on bacteria.  They then go on to describe 
hepatomegaly and tenderness accompanying amebic colitis without any 
evidence of hepatic infection.  The hepatic enlargement is thought to be 
a toxic response to intestinal infection, unrelated to the local presence 
of amebae.  <I inferred, perhaps wrongly, that 1) most cases of E.h. are 
confined to intestinal organisms only; especially given that in many 
parts of the world only cyst passers are treated; and 2) this liver 
condition would therefore occur more frequently than frank liver invasion>.

	Markel and Voege on the same page go on to question the 
significance of proposed etiology of "amebic hepatitis" and conclude by 
saying that it is clear that spread of the infection to the liver may 
occur in cases in which intestinal complaints never develop.

	Anyway, I stand corrected as to the significance of E.h. 
hepatitis but I still think parasites choose to live in the richest 
environment they can tolerate.

	Steve Kayes

On Fri, 15 Sep 1995, Graham Clark wrote:

> Stephen Kayes says:
> -But as regards the disease caused by Entamoeba, liver abscess 
> -from this organism is far less common than is amebic hepatitis which is 
> -caused by a toxin released from the parasite which is then transported to 
> -the liver by the hepatic portal system.  
> Whoa! Where did you get this from? Amebic hepatitis does not exist as
> a separate entity - signs/symptoms previously called amebic hepatitis
> (hepatomegaly, fever, and tenderness) are indicative of an early amebic 
> liver abscess. Liver abscess is reported to occur in about 10% of 
> patients with invasive disease.
> As far as the rest goes, I guess it is just a matter of perspective. I
> think almost anywhere in the blood stream or organs of the host would 
> provide a fairly rich source of nutrients for a parasite. I don't doubt 
> that selection helped determine where parasites reside in their hosts, 
> but I am not convinced that nutritional considerations were the major 
> driving force. 
> As you say, a dialogue on site selection by parasites would be 
> most interesting...
> Graham (entamoebologist)
> ___________________________
> C. Graham Clark, Ph.D.
> Laboratory of Parasitic Diseases,
> National Institutes of Health,
> Bethesda, MD 20892-0425, USA
> Tel: 301-496-4740
> FAX: 301-402-4941
> e-mail: gclark at nih.gov

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