During a blood meal, an infected mosquito (typically Mansonia spp and Aedes spp) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). They develop into adults that commonly reside in the lymphatics (2). The adult worms outwardly resemble those of Wuchereria bancrofti but are smaller. Female worms measure 43 to 55 mm in length by 130 to 170 micrometer in width, and males measure 13 to 23 mm in length by 70 to 80 micrometer in width. Adults produce microfilariae, measuring 177 to 230 micrometer in length and 5 to 7 micrometer in width, which are sheathed and have nocturnal periodicity (in some regions B. malayi may be sub-periodic, and note that microfilariae are usually not produced in B. pahangi infections). The microfilariae migrate into lymph and enter the blood stream reaching the peripheral blood (3). A mosquito ingests the microfilariae during a blood meal (4). After ingestion, the microfilariae lose their sheaths and work their way through the wall of the proventriculus and cardiac portion of the midgut to reach the thoracic muscles (5). There the microfilariae develop into first-stage larvae (6) and subsequently into third-stage larvae (7). The third-stage larvae migrate through the hemocoel to the mosquito's proboscis (8) and can infect another human when the mosquito takes a blood meal (1).
