To invade as a parasite.
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par·a·sit·ize also Brit par·a·sit·ise -sə-.tīz, -.sīt-.īz vt, -ized also Brit -ised; -iz·ing also Brit -is·ing to infest or live on or with as a parasite
par·a·sit·iza·tion also Brit par·a·sit·isa·tion .par-ə-sət-ə-'zā-shən, -.sīt- n
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para·si·tize (parґah-sĭ-tīz″) to live on or within a host as a parasite.Medical dictionary. 2011.