The following are true of kala-azar except –
**Core Concept**
Kala-azar, also known as visceral leishmaniasis, is a severe form of leishmaniasis caused by protozoal parasites of the Leishmania genus. It is characterized by a chronic infection of the reticuloendothelial system, particularly the spleen, liver, and bone marrow.
**Why the Correct Answer is Right**
Kala-azar is caused by the bite of an infected sandfly, which transmits the Leishmania parasites to the host. The parasites then infect the macrophages and reticuloendothelial cells, leading to a severe inflammatory response and tissue damage. The disease is typically characterized by symptoms such as fever, weight loss, and hepatosplenomegaly.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because kala-azar is not caused by a viral infection. The disease is caused by a protozoal parasite, Leishmania.
* **Option B:** This option is incorrect because kala-azar is not typically characterized by a rash. While some patients may develop a rash, it is not a hallmark symptom of the disease.
* **Option C:** This option is incorrect because kala-azar is not caused by a bacterial infection. The disease is caused by a protozoal parasite, Leishmania.
**Clinical Pearl / High-Yield Fact**
Kala-azar is a significant public health problem in many parts of the world, particularly in India, Bangladesh, and other countries in South Asia. It is often associated with malnutrition and other underlying health conditions, making it a major cause of morbidity and mortality in vulnerable populations.
**Correct Answer:** D. Kala-azar is caused by a protozoal parasite, not a viral or bacterial infection.