When an infected mosquito lands on a host and takes a blood meal, filarial larvae are deposited on the skin surface. They find their way through the bite wound and migrate to the lymph nodes, where they develop into adults. Once they have reached sexual maturity, they reproduce over their extensive lifespans to make millions of microfilariae (immature larvae) that circulate in the blood.

The human stage of the nematode life cycle comes to an end when another mosquito takes its blood meal, drawing up the immature larvae. The tiny worms have to be pretty quick about getting in position because, unlike their parents, they only live for a few months to a year. The microfilariae then burrow through the wall of their host’s midgut, to reach the muscle groups below. Here they mature into infective larvae, and migrate to the mosquito’s proboscis (the elongated sucking mouthpart) ready for transmission.

I’ve never studied parasite biology, but I find it really interesting. This life story in particular raises an important point: the worms reproduce sexually, so the host must have both male and female parasites to support a productive infection. Accordingly, years of exposure are required before serious disease can develop in the human host. However, the worms are patient, and adults will live for up to 8 years while they wait for a mate…