Leishmaniasis is a parasitic disease transmitted by infected sandflies, affecting the skin, mucous membranes, or internal organs, and is not sexually transmitted. Conversely, Syphilis (caused by Treponema pallidum), Chlamydiasis (by Chlamydia trachomatis), and Gonorrhoea (by Neisseria gonorrhoeae) are bacterial sexually transmitted infections (STIs).