What is Loa Loa?   Loa loa is a blood dwelling

nematode that is parasitic in humans. The adult worm wanders through the subcutaneous tissue but is most obvious as it crosses the conjunctiva of the eye hence leading to its common name, the African eye worm.

Like all roundworms, Loa loa is sexual so a male and female worm must be present in the same host for a full infection to ensue. Upon reproduction the female worm produces sheathed eggs called microfilariae which circulate in the blood stream.

Loa loa is endemic to parts of Western Africa, especially in the rainforests of the Congo and Sudan. Symptoms are less serious in natives of these areas with complications occurring mostly in visitors and tourists.

   Infection with Loa loa is spread by biting mango flies, a member of the genus Chysops. The American deer fly, Chysops atlanticus, had been reported to be a competent intermediate host of Loa loa and able to spread the worm to monkeys. This is of some public health concern but so far Loa loa has remained isolated to Africa.

   Treatment and management strategies are available and described in this website. Loa loa infection in endemic area complicates the mass treatment of Onchoceriasis, the disease of another nematode, with Ivermectin as its use in Loa loa patients might cause encephalitis.

Common Name : Eye Worm

Scientific Name: Loa Loa

Morphology

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.

Morphology

Nuclei, as shown above, are found in the tip of the tail and form a continuous row without large spacing between nuclei, differentiating Loa loa from Brugia malayi and Brugia timori, two nematode agents of lymphatic filariasis.

Morphology

Microfilaria are sheathed in a cuticle. The sheath, however, does not stain with Giemsa. Microfilaria have a diurnal periodicity to their concentrations in the bloodstream.

Signs and Symptoms Worms are often unnoticed as they

travel through subcutaneous tissues but can be painful as pass over the eyeball or bridge of the nose. Swelling of the conjunctiva and eye lid sometimes accompanies the worm's presence. Patients may describe literally seeing something crawl across their eye.

Signs and Symptoms

Signs and Symptoms Calabar swellings or local edema of the

subcutaneous tissue, are caused by an allergic reaction to dead worms or the metabolic products of the worms. The swellings are typically several inches in diameter and subside after a few days to a few weeks. They can be tender and painful. Calabar swellings can occur anywhere on the body but are often found on the forearms and wrists.

Signs and Symptoms

Signs and Symptoms

Complications may arise if worms lodge in unusual sites. Scrotal swelling, bowel obstruction, inflammation of renal glomeruli, endocarditis, retinopathy, arthritis, and peripheral neuropathy have all been seen in persons infected with Loa loa.

Signs and Symptoms

As is true with many parasites, Loa loa often increases the numbers of eosinophils, the immune cell that fights parasitic infections, in the blood.

Loa loa does not cause serious long term damage to humans.

Signs and Symptoms

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.

Signs and Symptoms

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, fatigue, and death.

Life Cycle

Vector/Transmission

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.

Vector/Transmission

The mango fly becomes infected through the uptake of Loa Loa microfilariae from a human upon taking a blood meal. The mango fly prefers forested areas and its larvae require wet, muddy places within the forest.

Diagnosis History in endemic areas, Calabar

swellings (see Clinical Presentation), and the presence of worm in the conjunctiva are the main methods of diagnosis. Laboratory tests for elevated eosinophils, C-reactive protein, and IgE quantification can be performed. Checking for microfilarial presence is not a reliable diagnostic test because microfilariae might take years to appear in the blood.

Management and Therapy

“Worm Removal”

Management and Therapy

  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.

Management and Therapy

Typical doses of DEC are 2mg/kg body weight three times a day for 3 weeks. Ivermectin is usually given at 200 mcg/kg body weight every 3 months for 2 years. Both drugs kill the microfilariae but not the adult worms.

DEC can be taken as a prophylactic at 300mg once a week.

Referenceshttp://www.stanford.edu/class/humbio103/

ParaSites2006/Loiasis/Index.htmlhttp://en.wikipedia.org/wiki/Loa_loa

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