Transmission of W. bancrofti is through the infective bite of a mosquito. The mosquito vector serves as a biological vector, as a stage of development occurs within it. Vectors include many various species of both Culex, Aedes and Anopheles mosquitoes. Most of these species feed nocturnally, and as a result, the microfilariae of W. bancrofti appears in higher levels within the blood at night than during the day. Unlike the B. malayi species, there is no known animal reservoir for W. bancrofti. (Reference 9).
The microfilaria of the W. bancrofti is shown here next to the wing of an Aedes mosquito, a common vector for its transmission. (Image 5)
Despite the large number of afflicted people, lymphatic filariasis is not easily transmittable. Infection requires a very high number of microfilaria, and this high level can only occur with many infective bites. People who have lived in an endemic area for a longer period of time have a greater risk of infection based on their extended risk of receiving a greater number of infective bites. As a result, the risk for the disease accumulates with age for populations remaining in endemic areas. Travelers, children, and other people who have not been in endemic areas for long periods of time, or haven't been exposed to many vectors, do not have a high risk for being infected with the disease (Reference 8).