  Using a model for rodent population dynamics, we study outbreaks of
Hantavirus infection induced by the alternation of seasons.
  Neither season by itself satisfies the environmental requirements for
propagation of the disease. This result can be explained in terms of the
seasonal interruption of the relaxation process of the mouse population toward
equilibrium, and may shed light on the reported connection between climate
variations and outbreaks of the dise ase.
