Loa loa

Background

• Also known as “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
• Unlike Onchocerciasis, Loa Loa does not damage visual acuity even while migrating through the eye

Parasite Lifecycle

• Human gets bit by infected fly => larvae travels through lymphatics => spend next 20 days maturing into adult nematodes => adult worms live and roam freely in subcutaneous tissues (unknown lifespan, but have been shown to live up to 17 years) => adult female worms release eggs that travel through lymphatics to mature in the pulmonary vasculature and then invade peripheral blood (estimated time of infection to time larvae can be detected in peripheral blood is >17 months; peripheral blood levels of larvae then increase until they hit a certain plateau, and then that plateau can be maintained for years)

Epidemiology

• >10 million people estimated to be infected worldwide
• 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

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

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, arthralgia or myalgias, 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)

Sub Q Swelling and Nodules

• Myiasis
• Tungiasis
• Loa loa
• African Trypanosomiasis
• Onchocerciasis

Ulcers

• Pyoderma
• Leishmaniasis
• Mycobacterium marinum

Linear and Migratory Lesions

• Cutaneous Larvae Migrans
• Photodermatitis

Evaluation

• 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 3-6mg/day and doubling daily until up to 400mg/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 200mg 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 or treatment-associated encephalopathy
  • Characteristically accompanied by retinal hemorrhages
  • Aphasia, incontinence, extrapyramidal signs
  • Generally fatal or resulting in severe morbidity

Disposition

• Discharge

See Also

• Parasitic diseases
• Travel medicine

References

Authors

Ross Donaldson