Leishmania

Leishmania is a protist
organism which causes Leishmaniasis. It is a Trypanosomatid parasite in the Euglenozoa phylum.
It is spread by sandflies of the genus "Phlebotomus" in the Old World, and of the genus "Lutzomyia" in the New World. 
Their primary hosts are vertebrates; Leishmania commonly infects hyraxes, canids, rodents, and humans. Leishmania currently affects 12 million people in 98 countries.
The parasite was named in 1903 after the Scottish pathologist William Boog Leishman.
Diseases.
The parasite causes three kinds of disease. Each type of disease is caused by different species of the parasite.
Structure.
"Leishmania" have a lipophosphoglycan coat on the outside of the cell. This is a trigger for toll-like receptor 2, a signalling receptor which triggers an innate immune response in mammals. The parasite can withstand the counter-attack by the immune system. There are treatments, which consist in helping the immune system to respond.