Sandfly transmission — DTM&H MCQ

Correct answer: E — Phlebotomine sandfly

The correct answer is E, Phlebotomine sandfly. Cutaneous leishmaniasis is caused by Leishmania species that are injected into the skin as promastigotes when an infected female phlebotomine sandfly (Phlebotomus in the Old World, including Syria) takes a blood meal; the parasites are then phagocytosed by macrophages, transform into intracellular amastigotes, and cause the chronic, often painless, cheek ulcer described. Syria and the wider Eastern Mediterranean and Middle East are highly endemic for Old World cutaneous leishmaniasis (L. tropica and L. major), and outbreaks have been well documented among conflict-affected populations and deployed military personnel bitten by sandflies in and around encampments. The diagnostic clincher, intracellular amastigotes on smear from the ulcer edge, is pathognomonic for Leishmania infection, and the only vector capable of transmitting this organism is the sandfly, confirming option E. Why the other options are wrong: D. Tsetse fly: this vector transmits African trypanosomiasis (sleeping sickness), an extracellular trypomastigote infection, not an intracellular amastigote skin disease, and tsetse flies are confined to sub-Saharan Africa, not Syria. A. Aedes mosquito: Aedes species transmit arboviruses such as dengue, chikungunya and Zika, none of which produce intracellular amastigotes or chronic cutaneous ulcers. B. Body louse: this vector transmits epidemic typhus (Rickettsia prowazekii) and relapsing fever (Borrelia recurrentis), causing systemic febrile illness, not a localised chronic skin ulcer with amastigotes. C. Ixodes tick: Ixodes ticks transmit Lyme disease and tick-borne encephalitis in temperate climates; they do not carry Leishmania and are not implicated in Syrian deployment exposures. Key point: Intracellular amastigotes on a chronic skin ulcer after Middle Eastern deployment signal Old World cutaneous leishmaniasis, transmitted exclusively by the bite of the phlebotomine sandfly.

Reference: NaTHNaC (National Travel Health Network and Centre), TravelHealthPro: Leishmaniasis, https://travelhealthpro.org.uk/disease/103/leishmaniasis