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Sadly I don't have any direct evidence, but what makes you think it wouldn't be that case? Since life began it's been a fight of various organisms to get the upper hand, surely a virus or a bacteria managed to be "too successful" at some point and wiped out its host.

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Well actually if a bacteria or a virus wiped out the host, being a single species, wouldn't be considered so successful as it won't have a host anymore to reproduce

Certain species of rats on Christmas Island in the Pacific went extinct due to a protozoa infection brought by fleas. I would imagine that this type of thing has happened regularly in both plants and animals. You have the introduction of a pathogen that doesn't wipe out a similar species and eradicates the new species. Although this is a plant example, the American chestnut was almost completely wiped out by a fungus that was probably brought over by the introduction of Japanese chestnut trees which are more resistant.

Most bacteria and viruses have multiple hosts. Wiping out a single one won't affect its viability.

Absolutely yes.

The risk is highly dependant upon the size of the population, how spread out said population is, if the pathogen is invasive to the population, and the creatures ability to evolve to tolerate said disease ( a factor related to its inherent diversity, life span, number off spring, and reproductive cycle) among others.

Another key consideration is that evolving to over come a pathogen or change in the environment might be enough for off spring (several generations perhaps) to live on but the old species to be classified as extinct.

Extinction and species are just fancy human ideas with limited definition and consistency. For example - neanderthals are considered extinct, but their genetic material remains in humans to this day. Likewise - no species really go extinct ofr just one reason but a multitude of environmental factors.

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Naturally occuring chytridiomycosis is a species of fungus that has made extinct about 90 species of frog within the last few decades.

That's about 1 in 16 known types of frog - now extinct.

Especially because the relationship between “multiple” hosts can be predator and pray, and if one becomes sick, or weaker, while the other is completely fine, it might be advantageous to kill off one of the hosts so that it can live in the stronger one.