4. Morphology
•Onchocerca volvulus is a filarial worm that causes onchocerciasis
•Has a five-stage life cycle
•Microfilaria are usually 300 X 8 mm long
•Adult male is usually 20-40 cm long; the female is usually 30-50 cm long
•Adults occur in the subcutaneous tissue and in nodules (Onchocercoma)
•An adult female worm can produce over 1000 microfilariae in a day
•Adult worms have a life span of 10-15 years
5. Epidemiology and geographical distribution
• Commonly known as river blindness / Robles' disease,
• Transmitted by blackflies of the similium species flies breed in fast-flowing streams and rivers
• The world’s 2nd leading infectious cause of blindness.
• global prevalence is 17.7 million, about 270,000 are blind, 500,000 are visually impaired by the
parasite
• Predominantly located in rural agricultural villages located nearwell oxygenated rapidly flowing
streams
• Tropical Africa (high endemicity in burkina faso and ghana)
• Foci are present in southern arabia, yemen and in america (mexico, guatemala, colombia, ecuador,
brazil, venezuela)
6.
7.
8. Pathology and pathogenesis
• Microfilariae released from the female worms that cause the most severe damage
• Migrating microfilariae, exclusively found in the interstitial fluids of the skin and subdermal tissues (not the
bloodstream),
• Cause
• changes in skin pigment
• loss of elastic fibers, “hanging groin,”
• other skin changes,
• severe pruritus
• accumulation of microfilariae in the vitreous humor
Visual clouding, photophobia, and ultimately retinal damage result in incurable blindness.
9. Forms of dermal onchocerciasis
• Acute papular onchodermatitis: small scattered itchy papules, +/- vesicles and pustules, +/- skin oedema,
often on the trunk and upper limbs.
• Chronic papular onchodermatitis: larger itchy, hyperpigmented, often flattopped, papules +/- areas of
hyperpigmentation.
• Lichenified onchodermatitis: itchy, hyperpigmented papulo-nodules or plaques which become confluent.
The itching is intense initially; the rash is asymmetrical, often affecting one or both legs.
• Atrophy: loss of elasticity with excessive wrinkles particularly on the buttocks; inelastic folds of inguinal
skin form hanging groins, often filled with enlarged lymph nodes.
• Depigmentation (leopard skin): patches of decreased pigment or loss contrasted with normally pigmented
skin around hair follicles.
10. Clinical features
• Intense itching
• Depigmentation of the skin
• Elephant skin
• Blindness
• Rashes
• Lesions
• Lymphadenitis
• General debilitation
• Serious visual impairment
11. Diagnosis
• Good hx
• Skin snip
• Slit-lamp examination of the anterior part of the eye
• Surgical removal and examination of nodules
• Serological test
12. Management
• ivermectin (mectizan) is administered as an oral dose of 150 micrograms per kilogram
(maximum 12 mg) every 6-12 months.
• drug binds to and activates glutamate-gated chloride channels by activating channels, drug causes
inhibitory postsynaptic potential ,microfilaria experience paralysis and then death
• Doxycycline is used to kill the wolbabchia bacteria that live in adult worms
• surgical removal of the nodules is also available.
14. Prevention
• Prophylactic ivermectin
• avoiding the day when the simulium blackflies tend to bite
• using insecticides such as deet
• wearing long sleeves and pants
15. References
• Cdc
• Jawetz microbiology 26th ed .Pdf
• Lange_microbiology_and_immunology_review_10th(7).Chm
• Oxford handbook of tropical medicine.Chm
