The SIRI stochastic model with creation and annihilation operators
  We generalize the well known formulation of the susceptibles, infected, susceptibles (SIS) spatial epidemics with creation and annihilation operators to the reinfection model including recovered which can be reinfected, the SIRI model, using ladder operators constructed from the Gell-Mann matrices known in quantum chromodynamics. 
Nico Stollenwerk, Maira Aguiar