Recent experiments demonstrate that persistent infections of lymphocytic choriomeningitis virus (LCMV) treated with fluorouracil cause a progressive debilitation of the infective ability of the virus that leads to eventual extinction. Interestingly, the replicative ability of the virus does not seem to be impaired by the mutagen in the course of the experiment. Such a behavior seems to rely on the presence of two different phenotypic traits (infective ability and replication rate) that are subject to different selection pressures in the environment where the infection proceeds [1]. We have designed a model that considers two coupled fitness traits affected in different extents by the mutagen. Our numerical and analytical studies demonstrate that a parasitic class is generated and that its action can lead to extinction of the whole population through elimination of individuals viable in only one of the traits. The parasitic population appears in bursts similar to those observed in the propagation of infective diseases. For finite populations, extinction takes place at any mutation rate below the usual error threshold, so it is a purely stochastic phenomenon that disappears as the population size diverges [2]. Our results are in full agreement with experimental observations.
[1] A. Grande-Pérez, E. Lázaro, P. Lowenstein, E. Domingo, and S. C. Manrubia, Suppression of viral infectivity through lethal defection. Proc. Natl. Acad. Sci. 102 (2005) 4448.
[2] J. Iranzo and S. C. Manrubia, Stochastic extinction of viral infectivity through the action of defectors, Europhys. Lett. 85 (2009) 18001.