CASES/YEAR
0 (US); 37,000,000 (Global)
OTHER NAMES
River Blindness; Onchocerca volvulus infection;
INCUBATION
About one year for larvae from bite of black fly to develop into microfilariae; [CCDM, p. 439]
INITIAL SYMPTOMS
Severe, intractable pruritus, localized papular eruptions, and conjunctivitis; [ID, p. 2370]
PRECAUTIONS
"No direct person-to-person transmission occurs." [CCDM, p. 440]
COMMENTS
FINDINGS:
Adult filarial worms produce microfilariae that migrate through the skin (dermatitis and nodules) and into the eye (visual impairment and blindness). "Leopard skin" pigmentary changes appear on the lower extremities. The skin nodules containing adult worms are called "onchocercoma." Massive enlargement of inguinal and femoral lymph nodes may occur. The disease varies by region probably because of different strains of the parasite: blindness in African savannas and skin disease in forests. [Merck Manual, p. 1674-5; CCDM, p. 438]
SKIN DISEASE:
Sowda is a skin disease that usually affects only one limb, and it is found in Yemen and central Sudan. [CCDM, p. 438] Onchodermatitis has been classified as: 1) acute papular dermatitis; 2) chronic papular dermatitis; 3) lichenified dermatitis; 4) atrophy; and 5) depigmentation. Sowda is a syndrome of hyperpigmented papules and plaques with associated regional lymphadenopathy. The most common symptom in expatriates is itching--an urticaria-like rash is often present on the trunk. Marked eosinophilia is associated with this infection. [Guerrant, p. 742-4, 943] Subcutaneous nodules are about 0.5-3 cm in size and usually detected over bony prominences. These onchocercoma contain the worms that can live for 9-14 years. Sonography can distinguish between onchocercoma and other subcutaneous nodules. [Cecil, p. 2137-8]
EPIDEMIOLOGY:
Travelers at risk are expatriate groups, such as missionaries, field scientists, and Peace Corps volunteers. Blackflies typically bite during the day near flowing rivers. [CDC Travel, p. 303] Local control programs have been very effective; [CCDM]
DIAGNOSTIC
Skin biopsy to identify microfilariae or adult worms; Characteristic eye lesions; Antibody tests to detect infection if microfilariae cannot be found; Serum antifilarial antibody tests available from CDC (404-718-4745): [CDC Travel]
SCOPE
99% of cases in sub-Saharan Africa (from Senegal and Ethiopia in the north to Angola and Malawi in the south); Focal endemic zones in Yemen, Venezuela, and Brazil; Has been eliminated in some areas; [CCDM]
SIGNS & SYMPTOMS
-
H eosinophilia
-
H lymphadenopathy
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O conjunctivitis, acute
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S lymphadenitis, acute
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S papules or plaques
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S rash (exanthem)
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S skin or subcutaneous nodule
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S urticaria
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*blindness
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*uveitis
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*weight loss
REFERENCES FOR CASES/YEAR
1.
2. (Global) OCP (1974-2002) used insecticides and brought under control in West Africa--40 million people relieved of infection; APOC launched in 1995 using drugs; [Fact sheets from WHO 2013] 37 million infected; [Harrison ID, p. 1140]