Which pathogen is responsible for causing Kala-azar?

Explanation

Kala-azar, also known as visceral leishmaniasis, is caused by the protozoan parasite Leishmania donovani. Other listed organisms cause different diseases: Plasmodium falciparum causes malaria, Entamoeba histolytica causes amoebiasis, Toxoplasma gondii causes toxoplasmosis, and Trypanosoma cruzi causes Chagas disease.