Loa loa

Background

• “African Eye Worm”
• Generally thought to be a harmless infection
• Neglected tropical disease - very few studies have been done; most information is from case reports
• Transmitted by Tabanid flies (genus Chrysops)
  • Mainly active during the day and prefer humans to other hosts
• Unlick Onchocerciasis Loa Loa does not damage visual acuity even while migrating through the eye
• Majority of cases in western and central Africa
  • Countries with the highest disease burden: Angola, Benin, Cameroon, Central African Republic, Chad, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Nigeria, Republic of Congo, Sudan

Risk Factors

• Living or traveling to western and central Africa
• Cases have been reported in urban and rural settings in these countries; however, majority occur in densely forested areas
• Working outside during the day, working in wet or muddy areas
• Prevalence higher in males, probably due to different occupational exposures
• Prevalence increases with age, probably due to chronicity of infection and lack of symptoms

Clinical Features

• Usually asymptomatic
  • Symptoms can begin within 2 months of exposure
  • Case reports suggests symptoms may not show up for >20 years post-exposure
• Infection is generally noticed when the patient sees a white worm migrating through the subconjuctiva or sclera of their eye
• Calabar swellings – pruritic transient swellings in the subcutaneous tissues as the worm migrates through, usually on the limbs, especially forearms, and near joints
• Pruritus, joint or muscle pain, headache
• Can cause severe disease rarely
  • Encephalopathy, endomyocardial fibrosis, pulmonary infiltrates, renal failure

Differential Diagnosis

Travel-related skin conditions

• Papules
  • Insect bites
  • Scabies
  • Seabather's eruption
  • Cercarial dermatitis (Swimmer's Itch)
• Macular
  • Chikungunya
• Sub Q Swelling and Nodules
  • Myiasis
  • Tungiasis
  • Loa loa
  • African Trypanosomiasis
  • Onchocerciasis
• Ulcers
  • Tropical pyoderma
  • Leishmaniasis
  • Mycobacterium marinum
  • Buruli ulcer
  • Dracunculiasis (Guinea Worm disease)
• Linear and Migratory Lesions
  • Cutaneous larvae migrans
  • Photodermatitis

See also domestic U.S. ectoparasites

Diagnosis

• Clinical diagnosis if you can see the worm in the subconjuctiva
• Marked eosinophilia and elevated IgE
• Presence of Loa Loa larvae in the blood, CSF, urine, or sputum – through microscopy or DNA PCR
  • Blood levels peak between 10 am – 3 pm
  • Difficult since adult worms must be depositing larvae to be detected, which they may not do for years and density of larvae may be too low to be detected
• Loa Loa antibodies in the serum

Management

• Eye worm removal
  • Use local anesthesia to make small incision in conjunctiva to extract worm with forceps
• Diethylcarbamazine (DEC)
  • Only treatment that is definitively curative killing both larvae and adult worms
  • May need 2-3 courses of treatment
  • First course should last 3-4 weeks
    • Starting doses should be divided into BID or TID doses starting at 3-6 mg/day and doubling daily until up to 400 mg/day is reached
    • Side effects occur in >50% of people – pruritus, rashes, edema, headaches, fever, pleural effusion, laryngeal edema
    • Give antihistamines or corticosteroids at the same time to reduce side effects
  • Associated with severe encephalopathy if Loa Loa burden is high
• 2nd line – Ivermectin or Albendazole
  • Ivermectin kills only larvae so is not curative, may be more effective if given monthly
    • Given as a single dose 150 ug/kg, then repeated every 1-3 months
  • Albendazole kills only adult worms so is not curative, treatment is very slow, and may not be effective if high worm burden
    • Given as 200 mg BID for 21 days
  • Both treatments may be more effective as a therapy to decrease disease burden so that follow-up treatment with DEC is less likely to cause encephalopathy

Complications

• Infection-associated encephalopathy
• Treatment-associated encephalopathy
  • Characteristically accompanied by retinal hemorrhages
  • Aphasia, incontinence, extrapyramidal signs
  • Generally fatal or resulting in severe morbidity

Prevention

• Personal protective measures against flies – long sleeves, light-colored clothes, nets/screens, insecticide
• Mass treatment in endemic communities is being currently evaluated to determine if it would be safe and effective

See Also

• Parasitic Diseases
• Travel Medicine