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derek a. zelmer zelmeda4 at WFU.EDU
Thu Jan 5 07:36:47 EST 1995

Dr. S.G. Kayes posed a question about virulence helping a parasite invade 
new territory. I'm not convinced that virulence itself aids in this, but 
I am sure that the conditions that would favor virulence would also favor 
infections into previously uninhabited hosts species. The conditions that 
favor virulence or allow virulence to develop require a probability of 
transmission that is high enough to negate the effects of host damage, as 
well as a relatively low degree of relatedness between the infecting 
strains. These conditions are most commoly found in overcrowded 
situations and can lead to epidemic outbreaks. During such an outbreak, 
the large number of parasites will result in a larger than normal 
absolute (not proportional) number of novel parasite genotypes as the 
result of recombination or mutation. It seems probable that such a 
concentration of parasites would create ideal conditions for the invasion 
of a new host species. Such an invasion would also be beneficial to the 
parasite species because of the increasing loss of susceptible hosts due 
to the outbreak. - Derek

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