Loiasis of eye. Close-up of a Loa loa worm wrigg- ling across a human eye. The eye is looking down- wards and the worm, which is long, thin and almost transparent, is just underneath the surface mem- brane (conjunctiva) of the white of the eye. Loa loa is a parasitic nematode that lives under human skin, causing itchy swellings and, occasionally, fever. The worms are spread by bloodsucking Chry- sops flies in tropical Africa, and reach 3-7cm when mature. They can sometimes be seen migrating across the surface of the eyes, where they cause irritation but do no serious harm. Loa loa worms can be destroyed by the drug diethylcarbamazine.