Loa loa is the filarial nematode

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

 (roundworm) species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 that causes Loa loa filariasis

Loa loa filariasis

Loa loa filariasis is a skin and eye disease caused by the nematode worm, loa loa. Humans contract this disease through the bite of a Deer fly or Mango fly , the vectors for Loa loa...

. It is commonly known as the "eye worm". Its geographic distribution includes Africa and India.

L. loa is one of four parasitic filarial nematodes that cause subcutaneous filariasis

Filariasis

Filariasis is a parasitic disease and is considered an infectious tropical disease, that is caused by thread-like nematodes belonging to the superfamily Filarioidea, also known as "filariae"....

 in humans. The three other filarial nematodes are Mansonella streptocerca

Mansonella streptocerca

Mansonella streptocerca, , is the scientific name of a human parasitic roundworm causing the disease of streptocerciasis...

, Onchocerca volvulus

Onchocerca volvulus

Onchocerca volvulus is a nematode that causes onchocerciasis or "river blindness" mostly in Africa. Long-term corneal inflammation, or keratitis, leads to thickening of the corneal stroma which ultimately leads to blindness. Humans are the only definitive host for O. volvulus. The intermediate host...

(causes river blindness), and Dracunculus medinensis

Dracunculus medinensis

Dracunculus medinensis is a nematode that causes dracunculiasis.Dracunculiasis, also known as Guinea worm disease, is caused by the large female nematode, Dracunculus medinensis, which is among the longest nematodes infecting humans. The adult female is primarily larger than the adult male. The...

(guinea worm).

Maturing larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e and adults of the "eye worm" occupy the subcutaneous layer of the skin – the fat layer – of humans, causing disease. The young larvae develop in horseflies of the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Chrysops (deer flies, yellow flies), including the species C. dimidiata and C. silacea, which infect humans by biting them.

Morphology

Loa loa worms have a simple body including a head, body, and tail. Males range from 20mm to 34mm long and 350μm to 430μm wide. Females range from 20mm to 70mm long and are about 425μm wide.

Life cycle

Three species involved in the life cycle include the parasite Loa loa, the fly vector, and the human host:

• A vector fly bites an infected human host and ingests microfilariase.
• Microfilariae move to the thoracic muscles of the insect host.
• Microfilariae develop into first stage larvae, then third stage larvae.
• Third stage larvae (infective) travel to the proboscis of fly.
• An infected vector fly bites an uninfected human host and the third stage larvae penetrates the skin and enters human subcutaneous tissue.
• Larvae mature into adults, who produce microfilariae that have been found in spinal fluid, urine, peripheral blood, and lungs.

Pathogenesis

Loa loa parasites infect human hosts by travelling through subcutaneous tissues such as the back, chest, groin, scalp, and eye. These parasites cause inflammation in the skin wherever they travel. If a parasite stops in one place for a short period of time, the human host will suffer from local inflammation known as Calabar swellings. These often occur in the wrist and ankle joints but disappear as soon as the parasite begins to move again. Parasites can also travel through and infect the eye, causing the swelling of the eye. Common symptoms include itching, joint pain, and fatigue.

Diagnosis and treatment

The main methods of diagnosis include the presence of microfilariae in the blood, the presence of a worm in the eye, and the presence of skin swellings. Surgical removal of the worm can easily be performed. The common treatment for the disease is a use of one of two drugs: diethylcarbamazine

Diethylcarbamazine

Diethylcarbamazine is an anthelmintic drug that does not resemble other antiparasitic compounds. It is a synthetic organic compound which is highly specific for several parasites and does not contain any toxic metallic elements.-Uses:...

 (DEC) or Ivermectin.