Infestation

wiktionary

ref

From Middle French infestation, from Late Latin infestatio. Morphologically infest +‎ -ation

etymonline

ref

infestation (n.)

early 15c., "a being infested," from Old French infestacion, from Late Latin infestationem (nominative infestatio) "a troubling, a disturbing, a molesting," noun of action from past participle stem of Latin infestare "to attack, disturb" (see infest).