Do some reservoir groups (e.g. bats) produce more zoonotic viruses than others? By cataloguing the accepted reservoirs for 415 viruses associated with mammals and birds, we show that there is currently no evidence for the existance of any such special reservoir groups. Instead, groups containing more reservoir species are associated with more viruses, and proportionally more zoonotic viruses.
Why most cross-species transmissions fail to establish ongoing transmission in the newly infected species remains poorly understood. Examining cross-species inoculations involving rabies, we show that mismatches in virulence which are predictable from host and viral factors make sustained transmission in the novel host less likely. These mechanistic insights help to explain and predict host shift events and highlight meta-analyses of existing experimental inoculation data as a powerful and generalisable approach for understanding the dynamics of index infections in novel species.