Will a virus cause the extinction of the human species?

Viruses have one purpose, replication. Viruses are considered obligate parasites, this means that viruses need a host to replicate (viruses essentially hijack the host cell's metabolic processes and use it for its own purposes), and if a virus fails to replicate it fails to survive. This is true for all viruses (if it has the ability to replicate without a host it, by definition, is not a virus).

I like to classify viruses as smart and dumb. A smart virus ensures that it can replicate by prolonging the life (or at least not directly killing) the host. The hepatitis viruses (namely Hep. A, B, and C) and Herpesviridae (which cause two well-known infections: herpes and chicken pox) oftentimes allow the host to live the rest of their lives without killing them directly. This ensures that the virus has a host and the ability to replicate, as soon as the host dies so too does the virus. Dumb viruses, by contrast, kill their host quite rapidly after infection (they're essentially maladapted). Ebola and Marburg viruses are examples of dumb viruses, they end up killing their hosts within 3 weeks of infection.

The problem with dumb viruses is that after 3 weeks, they have no host (if it does kill the host), the virus stops replicating, and subsequently dies with its host. Outbreaks the magnitude of what occurred in West Africa in 2014 are incredibly devastating and tragic make no mistake about it but these viruses have a very difficult time spreading. In order for the dumb viruses I've mentioned to spread from person to person someone needs to come into contact with a symptomatic person's bodily fluids (these viruses don't last long on dry surfaces [we're talking like 2 hours]). These viruses also limit mobility to the point where even the most hardened person is bed-bound and the symptoms are so distinctive that an afflicted person is easily spotted. This makes containment easier than something like the common cold.

Another thing worth quickly mentioning is our tremendous advancement in technology; even in the last 10 years we've come up with cures for diseases that were previously terminal (such as the Ebola vaccination) and as the technology at our disposal advances so to do the possibilities for a cure to previously incurable diseases.

Note: there are many other things that can be done to mitigate the spread of disease however they are considered inhumane at worst and highly controversial at best and for that I've decided to omit them.