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
[{'content': 'Which of the following infection gives a positive Casoni test? \nSelect and explain. \nA. Diphtheria, B. Scarlet fever, C. Echinococcus, D. Kala Azar', 'role': 'user'}, {'content': "Answer: C \nExplanation: Casoni's test is based on the principle of immediate hypersensitivity. The antigen used is hydatid fluid collected from animal or human cysts and is sterilised by Seitz or membrane filtration. 0.2 ml of the antigen injected intradermally. In positive cases a large wheal about 5 cm in diameter, with multiple pseudopodia like projections appears in 25-30 minutes. This is a sensitive test but not specific. Ref: Medical Parasitology By Bhatia, 3rd edition, Page 221.", 'role': 'assistant'}]