Overview
- Definition
Commonly known as “river blindness,” this eye and skin disease is caused by filaria (worm) Onchocerca volvulus, transmitted by female Simulium blackfly, which breeds in fast-flowing rivers
Second to trachoma as the most common infectious cause of blindness worldwide: >15 million people infected
- Symptoms
Photophobia, tearing, foreign body sensation
Decreased vision
Visual field constriction
Nyctalopia
- Laterality
Bilateral and symmetric
- Course
Several years may separate initial infection and clinical presentation
Untreated disease results in blindness
- Age of onset
Rare in children and teenagers, but increases in the third decade due to rising microfilarial load
- Gender/race
Males more commonly affected due to outdoor responsibilities
Most common in equatorial Africa, but also in Central/South America and Eastern Mediterranean
- Systemic association
Skin disease
20% of patients are co-infected with Loa Loa (Chap. 54), a fact bearing significant treatment implications
Exam: Ocular
Skin and eye diseases are caused by microfilaria (offspring) and not macrofilaria (mother). Ocular disease develops due to dead microfilariae, as living microfilariae are, in fact, well tolerated in the eye.
Anterior Segment
Conjunctivitis and 0.5- to 2-mm diameter conjunctival nodules
Limbal edema and hyperemia
Dead microfilariae can be seen directly in the cornea, appearing straight and opaque
Punctate or sclerosing keratitis
Anterior uveitis is rare and does not correlate with microfilaria load, and varies from low-grade, non-granulomatous to severe, turbid, granulomatous
Pupillary seclusion leading to angle closure glaucoma
Cataract
Posterior Segment
Pigment clumping and RPE atrophy, either diffuse or geographic with distinct borders, located temporal to the macula or nasal to the optic nerve
Cotton wool spots and intraretinal hemorrhage
Intraretinal worms can be seen as reflective opacities with green tint
Vascular sheathing
Optic neuritis resulting in optic atrophy and peripapillary hyperpigmentation
Exam: Systemic
Dermatitis papules is most common with pruritus at acute stage
Pretibial skin depigmentation (“leopard skin”)
Chronic disease results in skin lichenification and scarring, atrophy, pigment changes, especially on buttocks, waist, shoulders
Facial skin eruption and purplish lesions on upper body are rare but seen in Central America
Groups of round, painless, subcutaneous nodules with firm fibrous capsule containing adult worms (15–40 mm, lifespan 10 years)
Lymphatic obstruction with microfilariae, generally inguinal or femoral
Imaging
FA: mottled fluorescence around RPE atrophy
Visual field: diffuse constriction
Laboratory and Radiographic Testing
Sensitive, low-cost detection of antigens in tears, urine, dermal fluid
PCR assay with superficial skin scratch, or microscopic skin snip evaluation
Ultrasonography to detect and evaluate nodules
ELISA and radioimmunoassay test for parasite specific antibodies
Differential Diagnosis
Contact dermatitis
Scabies
Prickly heat
Insect bites
Leprosy, yaws, or superficial mycosis
Nodule differentiation from lymph node, lipoma, fibroma, dermal cyst, ganglia
Treatment
- Ivermectin is the treatment of choice
Kills microfilariae but not macrofilariae
Given at 150 mcg/kg in one oral dose every 6–12 months, both adults and children
Length of treatment depends on disease activity (continuous skin manifestation is a good gauge) and whether the patient still lives in endemic areas
However, serious and sometimes fatal adverse reactions occur in those co-infected with loiasis
- Doxycycline is emerging as a treatment to kill or sterilize macrofilariae
Kills Wolbachia, an endosymbiotic bacteria required for the survival of O. volvulus macrofilariae and embryogenesis
Given at 200 mg PO QD for 6 weeks
Since it does not kill microfilariae, ivermectin may still need to be given to reduce symptoms
Limited data suggest it may be safe in loiasis co-infection
Topical corticosteroids and cycloplegia to reduce ocular inflammation and positive pupillary seclusion and resultant angle closure glaucoma
Referral/Co-management
Dermatology and/or Interventional Radiology for nodulectomy