Modification of sand fly biting behavior by Leishmania leads to increased parasite transmission.

To attempt rodent-sand fly-rodent transmission of Leishmania major, laboratory-reared Phlebotomus doboscqi were fed on L. major-infected mice and then refed on uninfected mice 21 days later. Flies which refed either probed 1-2 times and took a full blood meal in less than 10 min or probed 3 or more times and took little or no blood during a period of 15 min or more. When dissected, 7 of 8 flies which experienced difficulty in obtaining a blood meal had flagellates in their cibaria, an observation supporting the hypothesis that parasites in this part of the alimentary canal modify normal blood feeding behavior. None of the infected females which probed 1-2 times had similar anterior station infections. Infected sand flies transmitted L. major to uninfected mice and a single fly, transferred from 1 mouse to the next while repeatedly attempting to take blood, infected 5 mice. During a year-long survey in Baringo District, Kenya, we collected 9,182 female sand flies. Only 2 of the 278 P. duboscqi captured during this collection were infected with L. major; however, 18 of the 789 small rodents from this area were infected with L. major. Parasite interference with normal blood feeding may explain how a relatively small population of P. duboscqi, only a few of which are infected with L. major, can amplify parasite transmission thereby maintaining a disproportionately large reservoir in local rodents.