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Infectious Diseases

Onchocerciasis

A chronic parasitic disease caused by the filarial nematode Onchocerca volvulus, transmitted by the bite of infected blackflies (Simulium species) that breed in fast-flowing rivers. Affects skin and eyes, major cause of blindness.

Also known as: River Blindness

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Referral and warning signs

When to refer

Refer suspected cases for diagnosis confirmation (skin snip). Refer for management initiation (Ivermectin/Doxycycline). Refer ALL patients with eye symptoms or visual impairment to Ophthalmology (RR) urgently. Refer patients from Loa loa endemic areas for risk assessment before Ivermectin.

Red flags

  • Any visual symptom (blurring, floaters, pain, photophobia).
  • Signs of severe skin inflammation or secondary infection.
  • Neurological symptoms after Ivermectin (suspect Loa loa reaction).

Signs and symptoms

  • Skin Manifestations:
  • - Onchocercomas (Nodules): Firm, non-tender, subcutaneous nodules containing adult worms. Usually over bony prominences (iliac crests, ribs, head, sacrum).
  • - Pruritus: Intense itching, often earliest and most troublesome symptom.
  • - Acute Papular Onchodermatitis (APOD): Itchy papular rash.
  • - Chronic Papular Onchodermatitis (CPOD): Larger, flatter, itchy papules.
  • - Lichenified Onchodermatitis (LOD): Hyperpigmented, thickened, scaling, severely itchy plaques ('lizard skin', 'elephant skin').
  • - Atrophy: Thinning, wrinkled skin ('presbyderma').
  • - Depigmentation: Patchy loss of pigment ('leopard skin'), often over shins.
  • Ocular Manifestations (River Blindness): Due to microfilariae migrating into eye.
  • - Conjunctivitis, photophobia.
  • - Punctate keratitis (snowflake opacities - reversible).
  • - Sclerosing keratitis (progressive corneal scarring -> blindness).
  • - Anterior uveitis / Iridocyclitis.
  • - Glaucoma.
  • - Chorioretinitis (inflammation of choroid/retina).
  • - Optic atrophy.
  • Leading to progressive, irreversible visual impairment and blindness.

Risk factors

  • Living near fast-flowing rivers where Simulium blackflies breed.
  • Occupations involving river exposure (farming, fishing).
  • Residence in endemic areas (Sub-Saharan Africa, Latin America, Yemen).

Diagnosis

Clinical assessment

Suspicion based on characteristic skin lesions (nodules, itching, pigment changes) and/or eye symptoms in person from endemic area.

Differential diagnosis

  • Skin: Scabies, Insect bites, Eczema, Fungal infections, Lichen planus, Leprosy, Lymphoma cutis, Vitiligo.
  • Eye: Other causes of keratitis, uveitis, blindness (Trachoma, Cataract, Glaucoma).

Investigations

  • Skin Snip Biopsy: Gold standard. Small, superficial skin shaving (usually from iliac crest or calf), incubated in saline, examined under microscope for emerging microfilariae. Multiple snips increase sensitivity.
  • Nodule Excision: Palpable nodules can be excised and examined for adult worms (confirmatory but not routine).
  • Slit Lamp Examination: Ophthalmologist can visualize microfilariae swimming in the anterior chamber or cornea.
  • Patch Test (Mazzotti Test): Application of DEC patch causes localized reaction (itching/rash) if microfilariae present (rarely used now due to systemic reaction risk with oral DEC).
  • Antibody tests (limited utility for active infection).
  • PCR on skin snips (research/specialized labs).

Diagnostic criteria

Clinical suspicion + Confirmation by identifying microfilariae in skin snip OR visualization in eye OR adult worms in nodule.

Management

Non-pharmacological management

  • Management of itching (antihistamines, emollients).
  • Surgical removal (nodulectomy) of easily accessible nodules may reduce adult worm burden but not curative.
  • Management of visual impairment (low vision aids).

Pharmacological treatment

  • Microfilaricidal Treatment (Mainstay - kills microfilariae, reduces symptoms/transmission, prevents eye disease progression):
  • - Ivermectin 150 mcg/kg PO single dose. Repeated every 6-12 months. Treatment is long-term (10-15 years or more) due to long lifespan of adult worms. (LOC: HC3+ / MDA Programs)
  • - Caution: DO NOT use Ivermectin if high suspicion of co-infection with Loa loa (another filarial worm endemic in Central/West Africa) due to risk of severe encephalopathy. Assess Loa loa risk before treating.
  • Adulticidal Treatment (Kills adult worms):
  • - Doxycycline 100-200mg PO daily for 4-6 weeks. Targets Wolbachia endosymbiont bacteria necessary for adult worm survival and embryogenesis. Leads to gradual death/sterility of adult worms. Often given before or with Ivermectin. (LOC: HC3+ / Specialist)
  • - Suramin (older drug, toxic, requires IV, rarely used now).
  • - Moxifloxacin (potential future role).
  • Management of Reactions: Mazzotti reaction (fever, rash, itching, adenitis after Ivermectin) usually mild, manage with antihistamines/analgesics. Steroids rarely needed.

Monitoring

Monitor symptoms (itching, skin lesions, vision). Monitor adherence to long-term Ivermectin treatment. Assess Loa loa co-infection risk before starting Ivermectin in relevant areas.

Complications

  • Severe chronic itching -> Skin damage, secondary infections.
  • Disfiguring skin changes (atrophy, depigmentation, lichenification).
  • Visual impairment / Blindness.
  • Social stigma, economic impact.
  • Severe adverse reactions to treatment (esp. if Loa loa co-infection).

Prevention

  • Mass Drug Administration (MDA): Community-directed treatment with Ivermectin (CDTI) annually or semi-annually in endemic areas.
  • Vector Control: Larviciding of blackfly breeding sites in rivers (historically successful in West Africa).
  • Personal protection (repellents, protective clothing - limited effectiveness).

Patient education

  • Explanation of Onchocerciasis cause (blackfly bite, worm infection).
  • Chronic nature of disease.
  • Importance of long-term Ivermectin treatment (prevents blindness, reduces itching/skin disease).
  • Potential side effects of Ivermectin (Mazzotti reaction).
  • Skin care for itching/dryness.
  • Importance of eye check-ups.
  • Role of MDA in controlling disease in community.

Uganda-specific notes

Endemic in specific foci associated with fast-flowing rivers (e.g., Mt Elgon region, West Nile, Western Uganda). CDTI programs are main control strategy. Eye complications are significant. Loa loa co-infection is NOT typically a major concern in Ugandan foci.

References

  • Uganda Clinical Guidelines (UCG) 2023

    Chapter 2, Section 2.4.5

  • National Onchocerciasis Control Programme Guidelines, MOH Uganda

    (Specific program documents)

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