- In visceral leishmaniasis (kala-azar), the spleen is the organ most frequently involved due to the parasite's predilection for the cells of the mononuclear phagocyte system.
- This leads to splenic enlargement (splenomegaly), which is often massive and a hallmark of the disease.
- The spleen becomes hypertrophic as it filters parasitized macrophages, contributing to symptoms such as anemia and leukopenia.
- Although the liver is also involved, splenomegaly is more prominent and characteristic.
- Lymphadenopathy is variable, and kidney involvement is rare.
- Thus, the spleen's role in parasite clearance explains its frequent and significant involvement in kala-azar.

Reference: Davidson’s Principles and Practice of Medicine, 23rd Edition, Chapter: Tropical Infectious Diseases, Page 1123.