Factors Of Parasitic Virulence

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cited (Esch and Fernandez 1993, Toft et
al. 1991) are evolutionary history and mode of transmission.
Incongruently evolved parasite-host associations are characterized by
high virulence, while congruent evolution may result in reduced
virulence (Toft et al. 1991). Parasites transmitted vertically (from
parent to offspring) tend to be less virulent than parasites
transmitted horizontally (between unrelated individuals of the same or
different species). Studies in which virulence is shown to increase
during parasite-host interaction, as in Ebert's (1994) experiment with
Daphnia magna, necessitate a synthesis of traditionally discrete
factors to predict a coevolutionary outcome. Authors prone to
habitually use the word decrease before the word virulence are
encouraged to replace the former with modulate, which emphasizes the
need for an inclusive, predictive paradigm for parasite-host
interaction.

Evolutionary history and mode of transmission will ...

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colonizations may occur regularly in epizootic-enzootic cycles. Sin
Nombre virus, a hemmorhagic fever virus, was epizootic in 1993 after
the population of its primary enzootic host, Peromyscus maniculatus,
had exploded, increasing the likelihood of transmission to humans
(Childs et al. 1995). Sin Nombre exhibited unusually high mortality in
human populations (Childs et al. 1995), which were being colonized by
the parasite.

It is assumed that coevolution of parasite and host will result
in decreased virulence (Esch and Fernandez 1993, Toft et al. 1991).
Sin Nombre virus was found to infect 30.4 % of the P. maniculatus
population, exhibiting little or no ...

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