This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: VBDs, Arboviral & Viral Infections, Surface Infections, Subject name: Social & Preventive Medicine
'rK 39 antigen' is useful for diagnosis of: 
Select and explain. 
A. Diphtheria, B. Diphtheria Tuberculosis, C. Lprosy, D. Kala azar
D: Kala azar
Answer: D: Kala azar 
Explanation: Antigens used in different tests: Test (disease) Antigen used Mantoux test PPD Lepromin test Dhamendra antigen Schick test Schick toxin Dipstick test- malaria Histidine rich protein type II Kala azar Rk 39 antigen