parasitize

verb

become a parasite to a host

Wiktionary

verb

Etymology: Etymology tree English parasite Proto-Indo-European *-id- Proto-Indo-European *-yéti Proto-Indo-European *-idyéti Proto-Hellenic *-íďďō Ancient Greek -ῐ́ζω (-ĭ́zō)bor. Late Latin -izōder. Middle French -iserbor. Middle English -isen English -ize English parasitize From parasite + -ize.

To live on or in a host organism as a parasite.
To behave as a parasite more generally.