Loiasis is caused by infection with the filaria Loa loa. The disease is endemic in forested and swampy parts of Western and Central Africa. The adult worms, 3–7 cm × 4 mm, chiefly parasitise the subcutaneous tissue of humans, releasing larval microfilariae into the peripheral blood in the daytime. The vector is Chrysops, a forest-dwelling, day-biting fly.

The host response to Loa loa is usually absent or mild, so that the infection may be harmless. From time to time a short-lived, inflammatory, oedematous swelling (a Calabar swelling) is produced around an adult worm. Heavy infections, especially when treated, may cause encephalitis.


The infection is often symptomless. The incubation period is commonly over a year but may be just 3 months. The first sign is usually a Calabar swelling, an irritating, tense, localised swelling that may be painful, especially if it is near a joint. The swelling is generally on a limb; it measures a few centimetres in diameter but sometimes is more diffuse and extensive. It usually disappears after a few days but may persist for 2 or 3 weeks.

A succession of such swellings may appear at irregular intervals, often in adjacent sites. Sometimes, there is urticaria and pruritus elsewhere. Occasionally, a worm may be seen wriggling under the skin, especially that of an eyelid, and may cross the eye under the conjunctiva, taking many minutes to do so.


The medicines that can be thought of use are:-

  • Mercurious
  • Ignatia
  • Euphrasia
  • Squilla