Not tending to safety; productive of evil.
Not salutary or wholesome; bad for health.
Extremely hostile or malicious; intensely acrimonious.
Of a pathogen: replicating within its host cell, then immediately causing it to undergo lysis.
Of a disease or disease-causing agent: malignant, able to cause damage to the host.
Of animals, plants, or substances: extremely venomous or poisonous.