The shape and form of protozoan parasites are inextricably linked to their 
pathogenicity. The evolutionary pressure associated with establishing and 
maintaining an infection and transmission to vector or host has shaped parasite 
morphology. However, there is not a 'one size fits all' morphological solution 
to these different pressures, and parasites exhibit a range of different 
morphologies, reflecting the diversity of their complex life cycles. In this 
review, we will focus on the shape and form of Leishmania spp., a group of very 
successful protozoan parasites that cause a range of diseases from self-healing 
cutaneous leishmaniasis to visceral leishmaniasis, which is fatal if left 
untreated.