Loiasis

Loiasis (African eye worm) is a filarial infection caused by Loa loa, transmitted by deer flies (Chrysops silacea and C. dimidiata), mainly in West and Central African rainforest (Cameroon, Gabon, Congo, DRC, Nigeria, Angola, South Sudan).

• Adult worms migrate through subcutaneous tissues for up to 17 years, with microfilariae showing diurnal periodicity (peak at midday).
• Many people are asymptomatic; expatriates and travellers present with more symptoms and with Calabar swellings.
• High microfilarial loads are a risk for severe adverse events (encephalopathy) after ivermectin.

• Calabar swellings: transient, non-pitting, painful or itchy angioedema, mainly on forearms and around joints, lasting 1 to 3 days.
• Eye worm: visible migration of an adult worm across the conjunctiva, with irritation and periorbital oedema.
• Pruritus, urticaria, fatigue, and muscle or joint pain.
• Complications: nephropathy (proteinuria, haematuria), cardiomyopathy, endomyocardial fibrosis, encephalopathy, and peripheral neuropathy; marked eosinophilia in travellers.

• Microscopy of daytime thick blood films (10:00 to 14:00) with Giemsa or Knott concentration to count microfilariae; or direct identification of the adult worm.
• LoaScope (rapid mobile microscopy quantification) for field screening.
• Serology (antifilarial antibody; cross reactivity), PCR, eosinophilia with raised IgE.
• Urinalysis and renal function; echocardiography if cardiac symptoms.
• Exclude onchocerciasis, other filariases, schistosomiasis, strongyloidiasis, and hereditary angioedema.

• Diethylcarbamazine (DEC): 8 to 10 mg/kg/day for 21 days, escalating from 50 mg on day 1 (3 doses), 100 mg on day 2, and 200 mg on day 3 to limit reactions; used when microfilaraemia is under 2,500 per mL, with antihistamines and corticosteroids (prednisolone 20 to 40 mg) to cover allergic reactions. A second course is often required.
• Albendazole 200 mg twice daily for 21 days if microfilarial load is high (above 8,000 to 30,000 per mL) to slowly reduce load, then DEC; apheresis can lower very high loads.
• Avoid ivermectin if microfilaraemia exceeds 20,000 to 30,000 per mL (risk of severe encephalopathy and death); treat with caution.
• Surgical removal of adult worm from the conjunctiva, and supportive care of renal and cardiac disease.
• Chemoprophylaxis for travellers: DEC 300 mg once weekly.