What are Leishmania?

Leishmania spp. (Kinetoplastida, Trypanosomatidae) are unicellular parasites with a digenetic life-cycle: promastigote forms live in blood-feeding phlebotomine sand flies and amastigote forms live in mammalian hosts where they replicate in cells of the immune system, predominantly macrophages. Survival in this environment requires specific adaptations for nutrient acquisition, tolerance of the harsh intracellular environment and strategies to protect the parasite against the defence mechanisms of the immune system.

Kinetoplastids are a large group of protozoa, which in evolution diverged early from other eukraryotes. Their cell biology has many of the conserved hallmarks of eukaryotes but also shows features that elaborated in specific, and sometimes extreme ways, or unique to this lineage. Their life styles are diverse, many live freely in soil and water, others are parasites of plants or invertebrates. Some have adapted to different niches within a mammalian hosts for parts of their life cycle; those that infect humans cause important neglected diseases in tropical and subtropical regions of the world.

350 million people globally are at risk of infection with Leishmania spp., with 0.6–1 million new cases of cutaneous leishmaniasis every year and up to 90,000 new cases of visceral leishmaniasis, which kills 26,000-65,000 people per year (WHO, 2019).

Disease burden is heaviest in the Indian subcontinent, across the middle East, North Africa and Central and South America, but sporadic outbreaks also occur in Southern Europe. Drugs that are currently used to treat leishmaniasis include pentavalent antimonials, Amphotericin B, paromomycin, pentamidine and miltefosine, all of which suffer from drawbacks, including severe side effects, limited efficacy, high costs and emerging drug resistance. There is no vaccine against human leishmaniasis and efforts to develop one are ongoing.

Read more about the complexities of combating this disease in this article in the MCID Newsletter 7, 2024.