Case: A 36-year-old man presents to the clinic with complaints of painful swelling in the right groin and intermittent fever for the past two weeks. He reports that the swelling began as a small lump, which progressively increased in size and became tender. He has also noticed a painless sore on his genital area about three weeks ago, which resolved spontaneously without treatment. Over the past week, he has experienced fatigue, malaise, and occasional night sweats. He denies urethral discharge, dysuria, or systemic symptoms such as weight loss or appetite changes. He is sexually active with multiple male partners and reports inconsistent condom use. On examination, the patient appears mildly unwell but is not in acute distress. Vital signs show a temperature of 100.8°F. Examination of the inguinal region reveals significant unilateral lymphadenopathy, with large, tender, and fluctuant lymph nodes on the right side. A palpable groove separating the enlarged nodes above and below the inguinal ligament is noted. There is no erythema or skin ulceration overlying the lymph nodes, but fluctuation suggests impending suppuration. Genital examination reveals no active lesions but mild scarring in the penile area, likely from the resolved sore. No rectal abnormalities are detected, and a neurological examination is normal. You suspect lymphogranuloma venereum in this patient. What is the causative agent of lymphogranuloma venereum (LGV)?
