Loa loa

                                        A worm just crawled across my eye!

                             Figure 1: An adult worm at the white portion of the eye

Loa loa is one of the eight parasitic nematode (roundworm) species that account for most cases of filariasis in humans. Loa loa is endemic to Africa. In particular, loiasis is really endemic to just a few Central and West African countries, where it afflicts around 20 million people. This nematode is often known as the African eye worm because the adult worm can sometimes be seen moving through the sclera (white portion) of the eye. Migration causes severe eye pain, inflammation, and sometimes blindness and may take a few minutes or up to several hours. Most cases of loiasis are asymptomatic. The first clinical signs may appear within a few months of infection, but often do not appear for more than a decade.

Loa loa live in areas with hot, wet climates, such as rainforests and swamps.

· Habitat Regions: tropical; freshwater

· Terrestrial Biomes: rainforest

· Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools

· Wetlands: marsh ; swamp

· Other Habitat Features: urban ; suburban ; agricultural ; riparian

Loa loa is an obligate endoparasite, feeding on fluids in the tissues of humans. Pharyngeal glands and intestinal epithelium produce digestive enzymes to feed on the hosts’ body fluids.

Chrysops silacea and C. dimidiata are the two species of Mango fly that transmit Loa loa to humans. Transmission occurs when Chrysops bites humans. Infective larvae from the mango fly are deposited on the skin and enter through the bite puncture. The mango fly becomes of infected through the uptake Loa loa microfilariae from a human upon taking a blood meal.

Figure 2: Morphology of the worm

Adult worms range in length from 2 to 3.5 cm for males and 5 to 7 cm for females. Both are no more than 0.5 mm wide. 

Surgical removal of the worm from the eye is easily performed after paralyzing the worm with a few drops of cocaine (4%). Patients can be treated with either DEC (Diethyl-carbamazine) or Ivermectin. However, both drugs may cause severe encephalitis, coma, or death in persons with high microfilariae loads. 

Prevention includes avoiding contact with the vector by using bug repellant, wearing long sleeved clothing and sleeping in screened areas.