Zheng Qi  2021-03-09

Core Vector Transmission Route

Leishmania parasites rely almost entirely on the bite of infected female phlebotomine sandflies to complete their natural transmission cycle. These tiny insects measure only 2 to 3 mm long, far smaller than common mosquitoes, and their bites are often so subtle that people rarely notice them immediately. Of the roughly 800 documented phlebotomine sandfly species worldwide, only around 30 are proven competent vectors capable of transmitating the parasite. Only female sandflies can drive transmission, as they require a blood meal to support the development of their eggs. When an uninfected female sandfly bites an infected human or animal reservoir host, it ingests Leishmania parasites along with the host’s blood. Over a developmental window of 4 to 25 days inside the sandfly’s gut, the parasites mature into highly infectious metacyclic promastigotes. When the infected female sandfly seeks out its next blood meal, it inoculates the new host with these infectious parasites through its bite, closing the core transmission loop.

Sandfly Habitat & Activity Traits

Phlebotomine sandflies are widely distributed across intertropical and temperate regions around the world, with distinct preferences for dark, humid, sheltered breeding sites. Female sandflies typically lay their eggs in rodent burrows, the crevices of old tree bark, abandoned ruins, wall cracks in residential homes, livestock shelters, and piles of household rubbish, where larvae can access abundant organic matter, stable warmth and consistent humidity to complete their growth cycle. Unlike many flying insects that travel long distances, most sandflies only forage for blood within a few hundred meters of their breeding sites, and their feeding activity peaks during the evening and nighttime hours, making nighttime outdoor activities in endemic areas a high exposure risk.

Rare Non-Vector Transmission Pathways

While sandfly bites account for over 90% of all documented infections, a small number of non-vector transmission cases have been clinically recorded. These rare routes include accidental direct contact with infected lesion exudate through broken skin, blood transfusion from asymptomatic infected carriers, congenital mother-to-child transmission, and even potential transmission through shared contaminated needles among intravenous drug users. These atypical pathways are far less common than the core sandfly-borne route, but they still pose hidden risks for vulnerable groups such as immunocompromised patients and people living with HIV in endemic regions.

Edited by: Secretariat of the Asia-Pacific Network for Drug and Diagnostics Innovation
Produced by: Zheng Qi
Reviewed by: Zhang Haobing
Tel: 021-64377008-2510 Fax: 021-54108329
Address: 207 Ruijin 2nd Road, Huangpu District,Shanghai, P.R. China  Postcode: 200025