The transmission of Leishmania infantum chagasi by the bite of the Lutzomyia longipalpis to two different vertebrates

Abstract

Background: Sandflies are vectors of Leishmania, the causative agent of leishmaniasis in mammalian hosts, including humans. The protozoan parasite is transmitted by the sandfly bite during salivation that occurs at the moment of blood feeding. The components of vector saliva include anticlotting and vasodilatory factors that facilitate blood flow and immunomodulatory factors that inhibit wound healing and quell the immune response. Not surprisingly, these factors also play important roles in the establishment of Leishmania infection. To date, the majority of knowledge that has been generated regarding the process of Leishmania infection, including L. infantum chagasi transmission has been gathered by using intradermal or subcutaneous inoculation of purified parasites.

Findings: This study presents the establishment of a transmission model of Leishmania infantum chagasi by the bite of Lutzomyia longipalpis, the vector of American visceral leishmaniasis. The parasites were successfully transmitted by infected sandfly bites to mice and hamsters, indicating that both animals are good experimental models. The L. infantum chagasi dose that was transmitted in each single bite ranged from 10 to 10, 000 parasites, but 75% of the sandflies transmitted less than 300 parasites.

Conclusions: The strategy for initiating infection by sandfly bite of experimental animals facilitates future investigations into the complex and dynamic mechanisms of visceral leishmaniasis. It is important to elucidate the transmission mechanism of vector bites. This model represents a useful tool to study L. infantum chagasi infection transmitted by the vector.

Figure 1

L. longipalpis sandfly biting a Balb/C mouse. A single sandfly was confined within a vial and allowed to bite the animal's entire ear. Note the blood engorgement of the sandfly (arrow). Inset: Dissected mouse ear showing the bite site as a small red dot (arrow).

Figure 2

Parasite numbers in infected L. longipalpis (2 to 14 days after the infective bloodmeal). Flies were infected by membrane feeding on mouse blood containing 4 million logarithmic phase promastigotes/mL. Midguts were dissected on the indicated days post-feeding and scored for numbers of viable parasites.

Figure 3

L. infantum chagasi transmitted to the mouse and hamster ears. The parasite numbers were obtained by real-time PCR of dissected ears at two hours after the bites. No significant differences were observed for parasite transmission by the various sandflies.

Figure 4

L. infantum chagasi transmitted to the mouse ears by a single infected L. longipalpis. Note that although the main number of transmitted parasites was about 1,000 the majority of the ears presented < 300 L. infantum chagasi.