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: Social & Preventive Medicine
The commonest vector of plague is: 
Select and explain. 
A. Xenopsylla cheopis, B. Musca domestica, C. Xenopsylla astia, D. Pulex irritans
A: Xenopsylla cheopis
Answer: A: Xenopsylla cheopis 
Explanation: Xenopsylla cheopis is the commonest and the most efficient vector of plague. Other vectors include Xenopsylla astia, Xenopsylla brasiliensis and Pulex irritans. Ref: Park 21st edition: page 268.