virulence

Judy Abel...T-L, CRESCENT HEIGHTS SR. HIGH JABEL at CBE.AB.CA
Mon Dec 19 16:54:50 EST 1994


I am currently borrowing an account to send this message, and my time is limited so I will only be able to touch on a few subjects...but I'll be back.
The main reason for this post is to appeal to those of you who are involved
in the field of parasitology or infectious disease to banish the word
"virulence" from use in the literature. I have seen it used to describe
parasite induced host mortality, as a relative measure of host damage, 
and, in the Ewaldian sense, as a measure of basic reproductive rate.
The term has never been clearly defined, which prevents any useful 
interpretation of selective mechanisms that could lead to its presence (or absence). The potential of a parasite to cause harm is its pathogenicity.
The damage caused is defined as pathology. Parasite induced host mortality
and basic reproductive rate require no further definition or labeling.
The same degree of host harm can come about through two very seperate
mechanisms, either by a slowly reproducing, highly pathenopgenic parasite,
or a relatively non-pathenogenic parasite with a high reproductive rate.
Both mechanisms are very different, and would result from very different ev
evolutionary and ecological mechanisms. Grouping all phenomena resulting
in host harm under the blanket of virulence does nothing more than
cloud the analysis of potential selective factors and evolutionary mechanisms.
			Derek A. Zelmer



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