jfgw wrote:odysseus2000 wrote:But effectively they do as if a virus kills all its hosts then it is gone, so the successful virus must not kill all its hosts.
A virus that infects more than one species could wipe one out completely while still being able to spread, however.
Almost all the "bad" introductions of diseases from another country take this form, the hosts in the native range have some immunity but their cousins in other countries don't - potato late blight (Irish potato famine), Dutch elm disease (a great example of a disease getting much worse over time incidentally), the current laurel wilt in North America that must be up there in terms of total biomass killed - 100's of millions of trees, citrus tristeza if you insist on a virus.