Loa loa

Background

Epidemiology

• Transmitted by Chrysops silacea and Chrysops dimidiata flies
  • Day biting flies, more common in rainy season and in rain forests
  • Attracted by fires and to rubber plantations
• Present in West and Central Africa, primarily in Equatorial Guinea, Gabon, Cameroon, Central African Republic, Congo (Brazzaville), DRC, Nigeria, Chad, Sudan, Angola, Ethiopia

Clinical Manifestations

• Often asymptomatic
• Most common symptom is Calabar swellings, a 10- to 20-cm painful, itchy subcutaneous swelling caused by migration of the adult worms
  • The lesions are essentially angioedema in response to the worm
• Worms can also migrate to the conjunctiva, where they are visible
• Infection can be complicated by hematuria and proteinuria

Complications of Treatment

• Treatment with antiparasitics may cause an increase in symptoms such as Calabar swellings or pruritis
• With treatment of high-level parasitemia, can cause fatal encephalopathy

Diagnosis

• Demonatration of microfilaria on Giemsa-stained blood film collected during daytime (10 am to 2 pm)
  • Also provides quantification of microfilarial burden

Management

• Not all infections require treatment
• Before treatment
  • Must rule out high-level microfilaremia (>2500-8000 microfilariae/mL) before considering medical treatment, due to the risk of encephalopathy
  • Rule out Onchocerca volvulus coinfection, as treatment with DEC can lead to blindness or exacerbation of skin disease
• If microfilaremia <8000 MF/mL
  • First-line treatment is diethylcarbamazine 8-10 mg/kg/day po divided tid for 21 days
    • Kills both the adult worms and microfilaria
  • After failing 2 rounds of DEC, albendazole 200 mg bid for 21 days
• If microfilaremia ≥8000 MF/mL, either:
  • Albendazole as above to decrease levels below 8000, followed by DEC as above
  • Apheresis to decrease levels below 8000, followed by DEC as above
• Levamisole 0.25 mg/kg p.o. once is a promising new treatment
• Can consider concomitant antihistamines or corticosteroids during the first week of treatment to decrease symptoms associated with treatment