Loiasis

Key Features

Essentials of Diagnosis

• Subcutaneous swellings; adult worms migrating across the eye

• Encephalitis, which may be brought on by treatment

• Microfilariae in the blood

General Considerations

• This chronic filarial disease is caused by infection with Loa loa

• Transmitted by chrysops flies, which bite during the day

• Over 6–12 months after infection, larvae develop into adult worms, which migrate through subcutaneous tissues, including the subconjunctiva (leading to the term "eye worm")

• Adults can live for up to 17 years

Demographics

• The infection occurs in humans and monkeys in rainforest areas of West and central Africa

• An estimated 3–13 million persons are infected

Clinical Findings

Symptoms and Signs

• Many infected persons are asymptomatic, but they may have high levels of microfilaremia and eosinophilia

• Transient subcutaneous swellings (Calabar swellings)

  • Develop in symptomatic persons

  • Are nonerythematous, up to 20 cm in diameter

  • May be preceded by local pain or pruritus

  • Usually resolve after 2–4 days but occasionally persist for several weeks

  • Commonly seen around joints and may recur at the same or different sites

• Visitors from nonendemic areas are more likely to have allergic-type reactions, including pruritus, urticaria, and angioedema

• Adult worms may be seen migrating across the eye, with either no symptoms or conjunctivitis with pain and edema

Differential Diagnosis

• Dracunculiasis

• Cutaneous larva migrans

• Gnathostomiasis

• Myiasis

• Filariasis

• Onchocerciasis (river blindness)

• Bacterial pyoderma

• Cysticercosis (with ophthalmic involvement)

Diagnosis

Laboratory Tests

• Obtain blood samples during the day to identify microfilariae in blood

• Failure to find microfilariae does not rule out the diagnosis

• Identification of a migrating eye worm is also diagnostic

• Serologic tests

  • May be helpful in persons from nonendemic areas who may be acutely ill without detectable microfilaremia

  • However, usefulness for residents of endemic areas is limited because most of them will have positive results

• Molecular methods, including field-friendly LAMP assays, are available to rule out loiasis before administration of ivermectin for the control of other filarial infections

Treatment

Medications

• Diethylcarbamazine

  • Treatment of choice

  • Eliminates microfilariae and has some activity against adult worms

  • Dosage: 8–10 mg/kg/day for 21 days

  • Repeat courses may be needed

  • Mild side effects include fever, pruritus, arthralgias, nausea, diarrhea, and Calabar swellings

  • Coadministration of antihistamines or corticosteroids can lessen side effects

• Ivermectin

  • Highly active against microfilariae but not adult worms

  • Entails a high risk of severe reactions

  • To reduce the risk, pretreatment with corticosteroids and antihistamines and escalating dosage of diethylcarbamazine have been used, but this strategy does not prevent encephalitis

• Strategies to treat patients with high parasite loads include

  • No treatment

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