Competition and coexistence in host-parasite systems: The myxomatosis case

Abstract

Co-circulation of several strains of parasites has been observed in many host-parasite systems. However, simple epidemiological models cannot sustain this coexistence. In this work we study the coexistence of viral strains in the myxomatosis case. Myxomatosis, a highly lethal disease of the European rabbit, has been used in Australia and Europe as a biological control of rabbit populations. A few years after its introduction, the original highly virulent strains were almost completely replaced by field strains covering a wide range of virulence. Here, we study several mechanisms that may explain the field observations. First we considered spatial heterogeneity. The establishment of any strain over regions occupied by host populations may delay the spread of any superior competitive virus strain, producing global coexistence in the long term. On the other hand, sub-populations with different resistance levels in epidemiological contact, as observed in the field, can maintain several different virus strains co-circulating. The second class of mechanism introduces diversity among hosts of a local population sharing a territory. We considered different classes of host resistance to myxomatosis: belonging to a resistance class is a random fact. Host age-dependent resistance is also especially considered. These types of population heterogeneity can sustain local coexistence for many years, although exclusion takes place for long enough periods. The concurrent action of both types of mechanisms could explain why the diversity of virus strains is sustained, and the local coexistence. Finally, we briefly discuss the influence of host genetic dynamics in the coevolution of the system. © The Society of Population Ecology and Springer-Verlag Tokyo 2004.