As an aside, I would argue that parasitically-driven disease is more than an inconvenient fact of nature but a critical component of ecosystems. At risk of hyperbole, I like to use the phrase 'parasites run the world'. For example, it is becoming more and more apparent in oceanic systems that phytoplankton blooms worldwide are probably more limited by viral load than by nutrient depletion (gross over-simplification, it is more than simple mortality but also the viral component of the microbial loop which is at play here). These annual (or more often) die-offs are driving forces in oceanic nutrient content in surface waters (i.e. they provide the raw materials for the next bloom) and sinking nutrients drive deep sea ecosystems, which area-wise is most of our planet.
Likewise I believe that in terrestrial systems the role of parasites (including or especially that gray area between parasitism and commensalism) is under appreciated. Parasites have been shown to actually increase the total biomass in certain closed systems, and I suspect this process is probably occurring on a larger scale but is harder to resolve.
I look at this as something of a monkey wrench in the creationist adage about disease being a negative consequence of the Fall.
Doctor Bashir: "Of all the stories you told me, which were true and which weren't?"
Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"