I used to (along with my advisor and some members of my lab) study treatment methods for leishmaniasis. We published a few peer-reviewed papers with our findings, so, I've spent a lot of time considering leishmaniasis and have a good understanding of its potential severity. Current treatment methods for it are expensive (especially for the developing nations which are often affected) and worse yet, resistance to current treatments are becoming commonplace.
No one knows about leishmaniasis though because it tends to only affect developing nations. It is (or was a few years ago at least) considered an classified as an orphaned disease by the World Health Oeganization because so few labs are working to develop treatments.
You should know that leishmaniasis kills thousands a year and leaves many more than that permanently scarred. Google it if you want to see the kind of scarring I'm referring to... And those are the lucky ones that only had cutaneous leishmaniasis and didn't die to visceral leishmaniasis.