Bartonella bacilliformis is a bacterium that causes the disease known as Carrion's disease, which is primarily found in the Andes region of South America. It is transmitted to humans through the bite of infected sandflies. The disease has two phases: the acute phase, characterized by fever and skin lesions, and the chronic phase, which can lead to severe anemia. This bacterium is a part of the Bartonella genus, which includes other species that can cause various diseases in humans. Diagnosis typically involves blood tests, and treatment usually requires antibiotics to eliminate the infection.