  We introduce a game inspired by the challenges of disease management in
livestock farming and the transmission of endemic disease through a trade
network. Success in this game comes from balancing the cost of buying new stock
with the risk that it will be carrying some disease. When players follow a
simple memory-based strategy we observe a spontaneous separation into two
groups corresponding to players with relatively high, or low, levels of
infection. By modelling the dynamics of both the disease and the formation and
breaking of trade relationships, we derive the conditions for which this
separation occurs as a function of the transmission rate and the threshold
level of acceptable disease for each player. When interactions in the game are
restricted to players that neighbour each other in a small-world network,
players tend to have similar levels of infection as their neighbours. We
conclude that success in economic-epidemiological systems can originate from
misfortune and geographical circumstances as well as by innate differences in
personal attitudes towards risk.
