Elephantiasis is a syndrome caused by infection with a nematode parasite called the filarial worm. The parasite is transmitted form human to human via the female mosquito and grows into an adult worm that lives in the lymphatic system of a human.
Eight filarial worms are known to affect humans and these can be divided according to the body area they affect, as follows:
- Subcutaneous filariasis is caused by infection with the parasites Onchocerca volvulus, Loa loa, and Mansonella streptocerca, which all occupy the fat layer of the skin.
- Lymphatic filariasis is caused by the parasites Wuchereria bancrofti, Brugia malayi, and Brugia timori, which live in the lymphatic system.
- Another group of filarial worms including Mansonella ozzardi and Mansonella perstans occupy the serous cavity of the abdomen (serous cavity filariasis).
It is the parasites that cause lymphatic filariasis that lead to elephantiasis and the features of this syndrome.
Life cycle of a filarial parasite
The filarial worm is transmitted between humans via the female mosquito. When the mosquito feeds on human blood, filarial worms that are in their third-stage of development penetrate the bite wound and go on to become adults that live in the human’s lymphatic system.
The adults produce microfilariae which move into the lymph and blood vessels, where they actively circulate. When a mosquito feeds, these microfilariae are ingested and move towards the mosquito’s gut and thoracic muscles where they become first-stage larvae and eventually third-stage larvae. These third-stage larvae move towards the mosquito’s proboscis, where they will be transferred to a human next time the mosquito feeds.
Local worker collecting Aedes mosquito larvae in Luzon, Philippines. Adult mosquitoes are vectors of parasite worms that cause filariasis. Image Credit: CDC
Reviewed by Sally Robertson, BSc