virulent

adj 1: extremely poisonous or injurious; producing venom; "venomous snakes"; "a virulent insect bite" syn deadly, venomous

2: infectious; having the ability to cause disease ant avirulent 3: harsh or corrosive in tone; "an acerbic tone piercing otherwise flowery prose"; "a barrage of acid comments"; "her acrid remarks make her many enemies"; "bitter words"; "blistering criticism"; "caustic jokes about political assassination, talk-show hosts and medical ethics"; "a sulfurous denunciation" syn acerb, acerbic, acid, acrid, bitter, blistering, caustic, sulfurous, sulphurous, venomous, vitriolic

Source: WordNet. Princeton University