Most successful parasites are those which do not

If the host dies, parasite won’t get food & shelter.Many parasites have evolved to be host-specific (they can parasitise only a single species of host) in such a way that bothhost and the parasite tend to co-evolve; that is, if the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to counteract and neutralise them, in order to be successful with the same host species.