What organism that weaken or kill their hosts?

Parasites are organisms that weaken or kill their hosts by living off them and often extracting nutrients, which can lead to the host's decline in health. Examples include tapeworms, which inhabit the intestines of their hosts, and certain protozoa like Plasmodium, which causes malaria and can be lethal. Additionally, some fungi, like the Cordyceps genus, infect and ultimately kill insects by taking over their bodies. These interactions highlight the complex relationships in ecosystems where one organism's survival can come at the expense of another.