The causal organism of Kala-azar is

Options

A. Plasmodium vivax
B. Leishmania donovani
C. Trypanosoma lewsii
D. Wuchereria bancrofti.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the causal organism of Kala-azar. Kala-azar is a disease, and we need to identify which organism is responsible for causing it.

2. **Reviewing the Options**: The options provided are:
- Plasmodium vivax
- Leishmania donovani
- Trypanosoma plesi
- Wuchereria bancrofti

3. **Analyzing Each Option**:
- **Plasmodium vivax**: This organism is known to cause malaria, not Kala-azar. Therefore, this option is incorrect.
- **Leishmania donovani**: This organism is known to cause Kala-azar (also known as leishmaniasis). It is a protozoan parasite spread by the bite of sand flies. This option is likely correct.
- **Trypanosoma plesi**: This organism is associated with infections in rodents and does not cause Kala-azar. Thus, this option is incorrect.
- **Wuchereria bancrofti**: This organism causes filariasis, which is a different disease. Therefore, this option is also incorrect.

4. **Conclusion**: After analyzing all the options, the correct answer is **Leishmania donovani**, as it is the causal organism of Kala-azar.

5. **Final Answer**: The causal organism of Kala-azar is **Leishmania donovani**.

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