Onchocerciasis (river blindness) :———-

Onchocerciasis is the result of infection by the filarial Onchocerca volvulus. The infection is conveyed by flies of the genus Simulium, which breed in rapidly flowing, well-aerated water. Adult flies inflict painful bites during the day, both inside and outside houses. While feeding, they pick up the microfilariae, which mature into the infective larva and are transmitted to a new host in subsequent bites. Humans are the only known hosts Onchocerciasis is endemic in sub-Saharan Africa, Yemen, and a few foci in Central and South America.

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It is estimated that 17.7 million people are infected, of whom 500 000 are visually impaired and 270 000 blind. Due to onchocerciasis huge tracts of fertile land lie virtually untilled, and individuals and communities are impoverished.                                                                                                                                                                            Clinical features :–

The infection may remain symptomless for months or years. The first symptom is usually itching, localised to one quadrant of the body and later becoming generalised and involving the eyes.

Transient oedema of partor all of a limb is an early sign, followed by papular urticaria spreading gradually from the site of infection. This is difficult to see on dark skins, in which the most common signs are papules excoriated by scratching, spotty hyperpigmentation from resolving inflammation, and more chronic changes of a rough, thickened or inelastic, wrinkled skin. Both infected and uninfected superficial lymph nodes enlarge and may hang down in folds of loose skin at the groins. Hydrocele, femoral hernias and scrotal elephantiasis can occur. Firm subcutaneous nodules > 1 cm in diameter (onchocercomas) occur in chronic infection. Eye disease is most common in highly endemic areas and is associated with chronic heavy infections and nodules on the head. Early manifestations include itching, lacrimation and conjunctival injection.

 

These lead to conjunctivitis, sclerosing keratitis with pannus formation, uveitis which may lead to glaucoma and cataract, and, less commonly, choroiditis and optic neuritis. Classically, ‘snowflake’ deposits are seen in the edges of the cornea.

Management :-

Ivermectin, in a single dose of 100–200 μg/kg, repeated several times at 3-monthly intervals to prevent relapses, is recommended. It kills microfilariae, and is non-toxic and does not trigger severe reactions. In the rare event of a severe reaction causing oedema or postural hypotension, prednisolone 20–30 mg may be given daily for 2 or 3 days. Eradication of Wolbachia with doxycycline (100 mg daily for 6 weeks) prevents reproduction of the worm.