Brugia Malayi - Transmission: Vectors and Reservoirs

Transmission: Vectors and Reservoirs

B. malayi is transmitted by a mosquito vector. The principal mosquito vectors include Mansonia, Anopheles, and Aedes mosquitoes. The mosquito serves as a biological vector – it is required for the developmental cycle of the parasite (see Life Cycle). The geographical distribution of the disease is thus dependent on suitable mosquito breeding habitat.

• The nocturnal periodic form is transmitted by Mansonia and some Anopheline mosquitoes in open swamps and rice growing areas. These mosquitoes tend to bite at night and appear to only infect humans. Natural animal infections are rare and experimental animals do not retain infection.

• The nocturnal subperiodic form is transmitted by Mansonia in forest swamps, where mosquitoes bite in the shade at any time. Natural zoonotic infections are common. Cats, dogs, monkeys, slow lorises, civet cats, and hamsters have all been successfully experimentally infected with B. malayi from man and may serve as important reservoirs.

The accumulation of many infective mosquito bites—several hundreds to thousands—is required to establish infection. This is because a competent mosquito usually transmits only a few infective L3 larvae (see Life Cycle), and less than 10% of those larvae progress through all the necessary molting steps and develop into adult worms. Thus those at greatest risk for infection are individuals living in endemic areas—short term tourists are unlikely to develop lymphatic filariasis.