The evolution of virulence in a vector borne disease

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The effect of infectious diseases is directly felt by humans in terms of illness and sometimes death, in particular in developing countries. Furthermore, recent epidemics such as foot and mouth have emphasized the importance of infectious diseases for agriculture in the developed world. Ecologists are also increasingly realising that parasites are also important in regulating many natural populations and communities. Disease, and in particular disease that is shared between more than one host are also increasingly implicated in the decline of many endangered species. We therefore need to understand why parasites casue the harm (virulence) that they do. This project will develop a model system in which we can test many of the theories of host parasite evolution. Infectious disease agents such as viruses typically have much shorter generation times than their hosts. Not only this they have huge populations and since they also tend to mutate rapidly, there is a vast potential for variation within their populations. This means that they can change rapidly through evolutionary time. Theoretical work has been developed that predicts changes in virulence under a wide range of situations. This work looks at how quickly the parasite reproduces in the host. High growth rate leads to high transmission but also causes more damage to the host and therefore higher virulence. Virulence is seen as an unfortunate by product from the point of view of both the parasite and the host, of increased transmission. As yet there is relatively little data that tests these assumptions. The key goal of this proposal is to use the honeybee-mite-viral interaction as a new model system to provide one of the first empirical tests of the evolutionary theory of viral virulence.