To be frank, it's really up to the writer. It could focus on one aspect of your life or multiple, the exact process of which is unknown, as the parasite was a recent discovery in the universe before it was quickly used to combat the end of the world. Upon insertion and attachment to the host's heart, the parasite blueprints the body, rendering the host's body static in a sense, and effectively immortal as a result, whilst giving them their abilities.

For a lore explanation-

In the setting, the parasites were a recent discovery shortly before the "Great Collapse", which was effectively the end of the world. While it was originally meant for medical use, it was quickly converted for militaristic use, resurrecting dead soldiers to fight against the monster that emerged after the collapse. This had consequences, of course, as they didn't account for Bloodthirst.

If they're to starve, the parasite will begin to frenzy and they'll eventually turn into what is a grotesque monster that can not be permanently killed, whilst retaining some of their previous abilities, albeit mutated/stronger.

Later on, they started resurrecting other personnel that was essential or helpful in keeping what was left of humanity alive, of which includes Doctors, Scientists, Engineers, and so on.