Development of Mansonella ozzardi in a black fly species of the Simulium sanguineum group from Eastern Vaupés, Colombia.

Development of the microfilaria of Mansonella ozzardi to the infective stage in a species of the Simulium sanguineum group from the Mitú area, Comisaría del Vaupés, Colombia is described. Development was synchronous, and by day 6 third-stage larvae were observed in the head of flies which had fed on two naturally infected volunteers. Simulium biting activity was high from January-March, during the dry season. Only 261 blood-fed Culicoides were collected from an infected volunteer; 40% of 43 dissected on day 0 had ingested microfilariae. However, only one of 129 C. caprilesi specimens dissected after day 2 was positive, containing a second-stage larva thought to be M. ozzardi. It is concluded that Simulium, rather than Culicoides are the principal vectors of mansonelliasis in the Mitú area.