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
"Casoni Test" is positive in: 
Select and explain. 
A. Diphtheria, B. Scarlet fever, C. Echinococcus, D. Kala Azar
C: Echinococcus
Answer: C: Echinococcus 
Explanation: Echinococcus