Rosborne, if there is no God and life in the universe has simply evolved, parasites are logically consistent. If there is a niche to fill, some life form will exploit it no matter what the cost to other species.
It may not be possible to design a world without things that are "bad" from someone's perspective, but it is possible to design a world without evil. And that's what I would expect of a perfect God.
I would cheerfully exterminate smallpox, parasitic worms, malaria, viruses and any other parasitic species whose existence torments us and benefits no other species. I would not exterminate mosquitoes (just the diseases they transmit) since other species depend on them for food. Flies serve a purpose (but they would not be allowed to torment living animals) as do predators.
Yes, there would still be death, but it would be quick and relatively painless. A good God would have designed bodies to function perfectly until they gave out all at once, like the wonderful one-hoss shay.