Parasites are dependent on their hosts for survival. Which organism do you think is better adapted to a parasitic lifestyle, one that is virulent and often kills its host, or one that only causes mild chronic illness in its host?

Answer 1

Wouldn't it depend on some other factors? Such as
the ability of the parasite to reproduce?
the ability of the parasite to shift to various hosts (such as sheep, humans, and pigs, and chickens)?
The ability of the parasite to mutate
The ability of the parasite to resist treatment?
The ability of the parasite to live in its host for a long period of time before it kills. see http://www.canismajor.com/dog/hartworm.html