"Pestilent" is a word in ENGLISH

To taint with morbid matter or any pestilential or noxious substance or effluvium by which disease is produced; as, to …

Noxious, pestilential, or foul exhalations from decomposing substances, filth, or other source.

Pest-bearing; pestilential; noxious to health; malignant; infectious; contagious; as, pestiferous bodies.

Hence: Mischievous; noxious; pernicious; morally destructive.

Any agent which, when introduced into the animal organism, is capable of producing a morbid, noxious, or deadly effect upon …