Chlamydia
It is termed a pathogen. It can be a bacterium, virus, fungus, and so forth.
A+students - Trypanosoma
Miotic agents cause the pupil of the eye to constrict, or become smaller. Mydriasis is the opposite, making the pupil dilate like when you go to the eye doctor.
Chlamydia trachomatis causes chlamydia.