This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Frei's test is used for the diagnosis of? 
Select and explain. 
A. Lymphogranuloma venereum, B. Tuberculoid leprosy, C. Histoplasmosis, D. Tuberculosis
A: Lymphogranuloma venereum
Answer: A: Lymphogranuloma venereum 
Explanation: Frei's Test: It is the intradermal skin test used for the diagnosis of Lymphogranuloma venereum. A heat inactivated LGV (0.1ml) grown in yolk sac of embryonated egg is injected intradermally on the forearm and a material prepared from non infected yolk sac on other forearm (control). The test is read after 48-72 hrs. An inflamatory nodule appears at the test site in 2 days reaching a maximum in 4-5 days. The skin test becomes positive 2-6 weeks after infection and remains positive for several years. Must know: Lepromin test is used for the diagnosis of Tuberculoid leprosy. Histoplasmin is used for the diagnosis of Histoplasmosis. Mantoux test is used for the diagnosis of TB. Ref: Ananthanarayanan & Paniker's ed- 8th pg 420.