The primary vector for Leishmania donovani, which causes visceral leishmaniasis, is the sandfly of the Phlebotomus species. This insect transmits the parasite through its bite, introducing the promastigote form into the human host. Unlike Anopheles mosquitoes (malaria vectors), tsetse flies (sleeping sickness vectors), or blackflies (onchocerciasis vectors), only Phlebotomus sandflies carry and transmit Leishmania donovani. Their role is critical for the parasite’s life cycle and disease transmission.

Reference:
Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 9th Edition, Volume 2, Chapter 114, p. 3179.