ONCHOCERCIASISMUDOOGO EDGAR

Objectives• Taxonomy

• Morphology

• Epidemiology and geographical distribution

• Life cycle

• Pathology and pathogenesis

• Clinical manifestation

• Diagnosis

• Treatment

• Prevention

Taxonomy KINGDOM: Animalia

PHYLUM: Nematoda

CLASS: Secernentea

ORDER: Spirurida

FAMILY: Filariidae

GENUS: Onchocerca

SPECIES: Volvulus

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

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)

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.

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.

Clinical features• Intense itching

• Depigmentation of the skin

• Elephant skin

• Blindness

• Rashes

• Lesions

• Lymphadenitis

• General debilitation

• Serious visual impairment

Diagnosis• Good hx

• Skin snip

• Slit-lamp examination of the anterior part of the eye

• Surgical removal and examination of nodules

• Serological test

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.

African programme for onchocerciasis control (1995)

Prevention• Prophylactic ivermectin

• avoiding the day when the simulium blackflies tend to bite

• using insecticides such as deet

• wearing long sleeves and pants

References

• Cdc

• Jawetz microbiology 26th ed .Pdf

• Lange_microbiology_and_immunology_review_10th(7).Chm

• Oxford handbook of tropical medicine.Chm

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