Visceral leishmaniasis causes –
**Core Concept**
Visceral leishmaniasis, also known as kala-azar, is a severe form of leishmaniasis that affects the internal organs, particularly the spleen, liver, and bone marrow. It is caused by the protozoan parasite *Leishmania donovani*.
**Why the Correct Answer is Right**
Visceral leishmaniasis occurs when the *Leishmania* parasite is ingested by macrophages in the reticuloendothelial system, leading to an accumulation of the parasite within these cells. The parasite then multiplies within the macrophages, causing them to become infected and release pro-inflammatory cytokines, which can lead to fever, weight loss, and other systemic symptoms.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because visceral leishmaniasis is not primarily caused by an allergic reaction.
**Option B:** This option is incorrect because visceral leishmaniasis is not primarily caused by an autoimmune response.
**Option C:** This option is incorrect because visceral leishmaniasis is not primarily caused by a bacterial infection.
**Clinical Pearl / High-Yield Fact**
Visceral leishmaniasis is a significant public health concern in many parts of the world, particularly in South Asia and Africa, where it is often transmitted through the bite of an infected sandfly.
**Correct Answer: A. Visceral leishmaniasis is caused by the protozoan parasite Leishmania donovani.**