Stochastic extinction of viral infectivity through the action of defectors

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.