Emerging infectious diseases are often the result of a host shift, where a pathogen jumps from one host species to another. Host shifts appear to be common, with the phylogenies of hosts and pathogens often showing incongruence, suggesting parasites have switched between host species. I became interested in host shifts following examining the phylogenies of sigma viruses, where we found that despite their mode of vertical transmission they have switched between host species during their evolutionary history (Figure 3).
I then went on to examine how the host phylogeny may be an important determinant of sigma viruses ability to infect a novel host, and have recently started to use Drosophila C virus to examine how pathogen virulence can change following a host shift. I have also looked at the evolution and host shifts of rhabdoviruses in arthropods. Drosophila and their natural viruses offer a unique and powerful system to test questions related to disease emergence, and I have a number of ongoing projects looking at various aspects of the evolution and ecology of parasite host shifts.