Loa loa		Contents		Rev 07/18/2022
Eye worm		Classification		Hosts
		Morphology and Anatomy		Life Cycle
Return to Loa Menu		Economic Importance		Damage
		Distribution		Management
Return to Onchocercidae Menu		Feeding		References
		Nemaplex Home Page		Go to Dictionary of Terminology

Classification:

Chromadorea
Chromadoria

 Rhabditida 

                               Spirurina

                                  Filarioidea

Onchocercidae

 

                 Loa loa Cobbold, 1864

        

Eye Worm

Type species of the genus: Loa loa Cobbold, 1864

A cutaneous filarial parasite of humans

Loa loa and three other filarial nematodes cause subcutaneous filariasis in humans.  The other are Mansonella streptocerca,Onchocerca volvulus (causes river blindness), and Dracunculus medinensis (guinea worm).

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Morphology and Anatomy:

Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:         

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Distribution:

More than 10 million people in western and central Africa are estimated to be infected with Loa loa filarial nematodes 

Like most other infectious diseases, L loa filariasis (loiasis) covers a wide range of symptoms. Severe complications have been reported; however, most observations are anecdotal, typically in travellers.

Human loiasis is generally confined to the rain forest and swamp forest areas of West Africa. It is especially common in Cameroon and on the Ogowe river.

(taken from Peters and Gilles1991)

As cited by Metzger and Mordmuller (2014) from Brain (1931): (quote) a single woman, aged 29, attended Dr O'Donovan's clinic at the London Hospital on December 17, 1930. Fifteen months ago she went to the coastal area of Nigeria as a missionary; on the boat returning to this country she noticed in a mirror a white worm about one inch long moving in the skin of the cheek toward the inner canthus of the left eye; she was advised to apply pressure to prevent the worm from entering the eye, and when she did so the worm retreated and disappeared (endquote)..

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Economic Importance:

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Feeding:

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Hosts:

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Life Cycle:

Loa loa - a filarial nematode causing loa loa filariasis primarily in Africa and India. First reported by Mongin (1770) in a French colony on the island of Hispaniola.

L. loa ind three other filarial nematodes cause subcutaneous filariasis in humans.  The other are Mansonella streptocerca, Onchocerca volvulus (causes river blindness), and Dracunculus medinensis (guinea worm).

In filarial nematodes, Two hosts to complete the life cycle, an intermediate host (often an arthropd) and a primary host (usually a vertebrate). The juvenile stages occur in the intermediate host and the reproductive adult in the definitive (primary) host.

• A vector fly bites an infected human host and ingests microfilariae.
• Microfilariae move to the thoracic muscles of the insect host.
• Microfilariae develop into first stage juveniles, second and third stage juveniles.
• Third stage juveniles are the infective stage and travel to the proboscis of fly.
• An infected vector fly bites an uninfected human host; the third stage juvenile penetrates the skin and enters human subcutaneous tissue.
• Juveniles mature into adults, which produce microfilariae that have been found in spinal fluid, urine, peripheral blood, and lungs.

Once inside the human body the infective larvae develop slowly into a mature adult (the process takes about a year). During this period it lives and moves around the fascial layers of the skin. In periods of growth and development Loa loa often makes frequent excursions through the subdermal connective tissues where it is often noticed by the host.

Once they reach maturity the adults mate and produce sheathed microfilariae 298 x 7.5 μm in size. Males range from 20mm to 34mm long and 350μm to 430μm wide. Females range from 20mm to 70mm long and are about 425μm wide.

The microfilariae closely resemble the microfilariae of Wuchereria bancrofti  however in stained films they assume a stiff angular attitude. The cuticle sheath also does not stain with Giemsa (see picture below taken from Peters and Gilles 1991).

The microfilariae are diurnally periodic in synchrony with their vector and once they reinfect a fly they undergo two stages of growth into infective larvae (in about 10 days time) which can then be transmitted back to humans.

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Damage:

Most of the pathological problems observed in people infected with Loa loa are connected to periods when the migrating adult worms appear near the surface of the skin. The worms often appear around the eye where they can be easily seen and extracted before they damage the conjunctiva (See pictures below taken from Peters and Gilles 1991).

Loa loa within human eye Image from Metzger and Mordmuller, 2014 Carmen L Ospina Salazar, Lambar, Gabon)

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Management:

The World Health Organization recommends diethylcarbamazine for treatment of patiants with loaisis infection (Metzger and Mordmuller, 2014). Ivermectin treatment is commonly used.

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References:

Brain, R.T. 1931. Loa-Loa. Proc. Royal Soc. Med 24:515-516.

Metzger, W.G., Mordmuller, B. 2014. Loa loa : does it deserve to be neglected?. The Lancet Infectious Diseases 14:353-357

Mongin, A. 1770. Sur un ver trouve sus la conjunctive a Maribarou, isle Saint-Dominique. J Med Chir Pharm Paris, 32 :38-339.

Mongin, A. 1770. Sur un ver trouve sus la conjunctive a Maribarou, isle Saint-Dominique. J Med Chir Pharm Paris, 32 :38-339.

Peters, W. and Gilles, H.M. (1991) A Colour Atlas of Tropical Medicine and Parasitology. Third edn., Wolfe, London.

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Copyright  1999 by Howard Ferris.
Revised: July 18, 2022.