Conceptual diagram of a potential SIR (susceptible - infected - recovered) model

A conceptual box-and-arrow diagram of avian influenza transmission. In each box, the first letter indicates low pathogenic avian influenza (LPAI) infection status (susceptible, infected, recovered) and the second indicates highly pathogenic avian influenza (HPAI) infection status. Viral reservoirs V1 and V2 represent LPAI and HPAI environmental reservoirs, respectively. Dashed lines represent viral shedding into the environment.