Virulence — the harm a pathogen does to its host — can be extremely high following a host shift (for example HIV, SARs and Ebola), while other host shifts may go undetected as they cause few symptoms in the new host. To examine how virulence changes following a host shift I carried out an experiment with 48 species of Drosophilidae and Drosophila C virus (DCV) looking at why virulence differs between different host species.
I found that host shifts resulted in dramatic variation in virulence, with benign infections in some species and rapid death in others. The change in virulence was highly predictable from the host phylogeny, with hosts clustering together in distinct clades displaying high or low virulence. High levels of virulence are associated with high viral loads, and this likely determines the transmission rate of the virus (Figure 5 below). Click here to see a video of virulence changes across the host phylogeny at different time points post infection or read the paper here.