Just as Xenopsylla is to Yersinia pestis, so is:

Options

A. Glossina palpalis to Wuchereria ban- crofti
B. Culex to Plasmodium talciparum
C. Homo sapiens to Taenia solium
D. Phlebotomus to Leishmania donovani

Answer

To solve the analogy "Just as Xenopsylla is to Yersinia pestis, so is:", we need to identify the relationship between the first pair and then find a second pair that shares a similar relationship.

### Step-by-Step Solution:

1. **Identify the First Pair**:
- Xenopsylla is a genus of fleas, specifically known as the rat flea.
- Yersinia pestis is the bacterium that causes the plague.

2. **Determine the Relationship**:
- The relationship here is that Xenopsylla (the vector) transmits Yersinia pestis (the pathogen). In this case, Xenopsylla is a vector for the disease caused by Yersinia pestis.

3. **Find a Similar Pair**:
- We need to find another vector and its corresponding pathogen.
- The correct answer is Phlebotomus and Leishmania donovani.

4. **Explain the Second Pair**:
- Phlebotomus is a genus of sandflies that act as vectors for Leishmania donovani, which causes kala-azar (also known as black fever).

5. **Conclusion**:
- Therefore, just as Xenopsylla is to Yersinia pestis, Phlebotomus is to Leishmania donovani.

### Final Answer:
Phlebotomus is to Leishmania donovani.