This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parasitology, Subject name: Microbiology
The rk39 antigen is used in the diagnosis of: 
Select and explain. 
A. Tuberculosis, B. Trypanosomiasis, C. Toxoplasmosis, D. Kala azar
D: Kala azar
Answer: D: Kala azar 
Explanation: Ans. D. Kala azara. k-39 antigen is a 39-amino acid residue encoded by a kinesin-related gene in the amastigotes of Leishmania causing Kala azar.b. Anti-k39 antibodies are secreted into various body fluids such as urine and sputum along with blood, and have been shown to be useful in the diagnosis of VL.c. Enzyme-linked immunosorbent assay (ELISA) and ICT assays use a recombinant rk39 antigen to detect these antibodies in serum in patients of Kala azar.