2003 The Society for the Study of Evolution. All rights reserved.
Evolution, 57(7), 2003, pp. 14891497
WITHIN-HOST PARASITE DYNAMICS, EMERGING TRADE-OFF, AND EVOLUTION OF
VIRULENCE WITH IMMUNE SYSTEM
JEAN-BAPTISTE ANDRE´ ,1,2 JEAN-BAPTISTE FERDY,1,3 AND BERNARD GODELLE1,4
1Laboratoire Ge´nome, Populations, Interactions, Adaptation, UM2-IFREMER-CNRS UMR 5000,
Universite´ Montpellier II-CC 063, Ba^timent 13, RdC, Place Euge`ne Bataillon, 34095 Montpellier Cedex 5, France
Abstract. Virulence is an evolutionary paradox because parasites never benefit from their host's death. The adaptive
explanation of virulence is classically based upon the existence of physiological constraints that create a trade-off
between parasites' epidemiological traits (virulence, transmissibility, and clearance). Here we develop an epidemio-
logical model where infections are dynamic processes and we demonstrate how these dynamics generate a trade-off
between emerging epidemiological parameters. We then study how host's immune strength modifies this trade-off
and hence influences virulence evolution. We found that in acute infections, where parasites are engaged in a race
with immune cells, immunity restrains more the duration of the infection than its intensity. As a consequence parasites
evolve to provoke more virulent but shorter infections in strongly immunized hosts.
Key words. Acute infections, evolution of virulence, microparasites, specific immunity, trade-off, within-host models.