Visceral leishmaniasis is a severe form of leishmaniasis caused by the parasite Leishmania donovani. It primarily affects internal organs, particularly the spleen, liver, and bone marrow. The disease is transmitted through the bite of infected sandflies, which are most commonly found in tropical and subtropical regions. Symptoms of visceral leishmaniasis include fever, weight loss, anemia, and swelling of the spleen and liver. If left untreated, it can be fatal. Diagnosis typically involves blood tests or bone marrow examination, and treatment usually includes medications such as antimonials or liposomal amphotericin B.