Which organism causes Kala-azar?

Leishmania

The correct answer is Option (4) - Leishmania

Leishmania is the organism that causes Kala-azar.

Kala-azar:

• Kala-azar, also known as visceral leishmaniasis, is a disease caused by the protozoan parasite of the Leishmania genus.
• The primary species responsible for causing Kala-azar is Leishmania donovani.
• It is transmitted to humans through the bite of infected sandflies.
• Kala-azar affects the spleen, liver, bone marrow, and other organs, causing symptoms such as prolonged fever, weight loss, swelling of the spleen and liver, and anemia.

The other organisms mentioned (Escherichia coli, Azotobacter, Clostridium) are bacteria and are not associated with causing Kala-azar.