Leishmania is a genus of parasitic protozoa that causes leishmaniasis, a disease transmitted primarily by the bite of infected female sandflies. There are several species of Leishmania, and they can lead to different forms of the disease, including cutaneous, mucocutaneous, and visceral leishmaniasis. The parasites live inside the immune cells of their hosts, where they can evade the immune response. Symptoms vary depending on the type of leishmaniasis but may include skin sores, fever, and weight loss. Treatment often involves medications that target the parasites, but prevention focuses on avoiding sandfly bites.