How 'bout some clarification!

Mark Siddall mes at
Thu Aug 4 11:14:36 EST 1994

In article <ADDUECK.9.2E40F025 at> ADDUECK at (Andrew Dueck) writes:
>	Ok, I have a question about hosts in the life cycle of parasites.  
>Specifically what is the difference between primary, secondary and alternate 
>hosts?  I think I can remember reading that primary hosts are the site of 
>sexual reproduction for the parasites, but I'm not sure if that's right.  
>Also, are secondary hosts and alternate hosts the same thing?

Actually, I think the terms you are looking for are "definitive" and
"intermediate" hosts.  Definitive is where the sexual phase of 
the parasite takes place (usually difficult to get people to 
acknowledge that mosquitoes are the definitive hosts for malaria
parasites - but such _is_ the case).  Intermediate hosts are 
any other host.  Primary and secondary intermediate hosts refer to their
sequence in a life history after leaving the definitive host.  For
example, definitive host of a trypanorynch cestode is a skate, primary
intermediate host is a crustacean, and secondary intermediate host is
a flatfish (I think).

Alternate host would simply be a host that is less frequently (or 
even as frequently) infected whether it be definitive or intermediate.


Mark E. Siddall                "I don't mind a parasite...
mes at                    I object to a cut-rate one" 
Virginia Inst. Marine Sci.                     - Rick
Gloucester Point, VA, 23062

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