Leishmaniasis vaccination. Young girl receiving a leishmaniasis vaccine. This tropical disease is caused by Leishmania sp., a parasitic protozoan, which is transmitted by bites from infected sand- flies. Vaccines contain dead or weakened disease- causing organisms. Following vaccination, the immune system becomes sensitized, preparing the body for the disease if infection does occur. In the more serious form, visceral leishmaniasis (kala-azar), there is fever, spleen enlargement, liver damage, and, without treatment, sometimes even death. The other form, cutaneous leishmaniasis, results in the development of an ulcer around the bite. Photographed in Iran.