Different Leishmania species in many geographic regions cause disease. The parasites develop and multiply in the gut of the sandfly until they are introduced into the blood and tissues of the human host. They infect the reticuloendothelial system and then multiply. When the infected cells rupture, the infection spreads to other organs.
Body temperature is an important factor that determines the localization of leishmanial lesions.
Species causing cutaneous leishmaniasis cannot grow at core body temperature, while species causing visceral leishmaniasis are able to grow at these temperatures. In cutaneous leishmaniasis, the hallmark of the disease is skin lesions, which can spontaneously heal in 2-10 months. In mucocutaneous leishmaniasis, mucosal ulcerations usually develop by metastasis rather than by local spread. Secondary infection plays a prominent role in the size and persistence of ulcers. Their progression is slow and steady.