Promastigotes of Leishmania are transmitted to human skin by the bite of a sandfly.
Some species tend to cause cutaneous leishmaniasis (e.g., L. major and L.tropica), whereas some species tend to cause visceral leishmaniasis (e.g., L. infantum and L. donovani), though emerging research (due to high deployment rates of western countries to indigenous areas) is showing these species specific presentation lines are blurring.