Definition of Loiasis

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Loiasis: The disease caused by the eye worm known as loa loa, a parasite that lives in humans and other primates. People contract the parasite when bitten by infected deer flies. The larvae of the worm enter the bloodstream and later develop into adult worms. Symptoms may not appear for months or years after the bite of the fly. The worms migrate through the skin causing local inflammatory reactions called Calabar swellings. The worms can often be seen migrating across the conjunctiva and cornea of the eye. Hence, the name "eye worm." The worm sometimes enters the brain causing encephalitis. The microfilarial (tiny thread-like) form of the worm is found in blood and lymphatic fluid during the day and in the lungs at night. The insect vector (that carries the parasite) is the deer fly Chrysops which lives in swampy areas of the forest, principally in the Congo River region, Sudan, and Ethiopia. Diagnosis is by detection of the microfilariae in the blood. Protective measures against the flies include the use of a repellent, long-sleeved shirts and long pants, and the use of bednets when sleeping. Treatment is with diethylcarbamazine (DEC) or ivermectin (Stromectol). DEC can also be used for prophylaxis. Loiasis is also known as lymphatic filariasis.

Loiasis: Incidence, age and sex
It is estimated that 12-13 million people worldwide are infected with Loiasis. It usually occurs in epidemic proportions in few areas of West and Central Africa. The incidence of the disease tends to increase with age. Both sexes are equally involved.

Signs and symptoms of loiasis: Diagnosis
Most of the infected individuals do not present with any symptoms. The worms usually migrate within the subcutaneous tissue (just under the skin) and wander to the conjunctiva of eye. This may result in red, itchy swellings under the skin called Calabar swellings. These swellings may last for 1 – 3 days. The passage over the eyeball can be sensed, but it usually takes less than 15 minutes. Sometimes the movement of eyeball may become painful.
A comprehensive physical examination may reveal ‘Calabar swellings’ which help in detection of the disease. Blood test will show a raised eosinophil count in most of the affected individuals. Identification of larvae by microscopic examination is a practical diagnostic procedure. Antigen detection by immunoassay using circulating filarial antigens is another useful diagnostic approach. Eosinophilia is detected in all cases.

Causes and prevention of loiasis
Loiasis is transmitted to humans by the bite of deer fly or mango fly. These vectors are blood-sucking and bite during the day. The mature male and female forms mate inside human body to produce more microfilaria.
DEET containing insect repellent, permethrin-soaked clothing and thick long- sleeved and long – legged clothing may be worn to decrease susceptibility to the bite of mango fly or deer fly. As these vectors are day-biting, the mosquito nets provide no protection. Diethylcarbamazine (DEC) is an effective prophylactic drug for loiasis infection. The recommended prophylactic dose is 300mg of DEC given orally, once weekly. No vaccine has been developed yet.

Loiasis: Complications
Encephalitis (inflammation of the brain tissues) can occur due to dead microfilaria occluding the vessels of the brain or spinal cord. Cerebral oedema may be found in fatal cases.

Loiasis: Treatment
The current drug of choice for therapy is diethylcarbamazine (DEC). It is given orally in a dose of 6mg/ kg/day taken 3 times daily for 12 days. .The pediatric dose is the same. DEC is mainly effective against larvae (immature worms) as compared to adult worms. Surgical removal of worms from conjunctiva may be considered in occasional cases.
 

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