Onchocerciasis: Treatment, symptoms, advice and help
Onchocerciasis (river blindness) is a parasitic disease caused by infection by a roundworm Onchocerca volvulus.
Onchocerciasis: Incidence, age and sex
Onchocerciasis is endemic in sub-Saharan Africa, Yemen, and a few foci in Central and South America. It is estimated that 17.7 million people are infected, of whom 500 000 are visually impaired and 270 000 blind.
Signs and symptoms of onchocerciasis: Diagnosis
The infection may remain symptomless for months or years. The first symptom is usually itching, localized to one quadrant of the body and later becoming generalized and involving the eyes. Transient oedema of part or all of a limb is an early sign, followed by papular urticaria. Chronic changes lead to a rough, thickened or inelastic, wrinkled skin. Both infected and uninfected superficial lymph nodes enlarge. Firm subcutaneous nodules > 1cm in diameter (onchocercomas) occur in chronic infection. Eye disease is most common in highly endemic areas. Early manifestations include itching, lacrimation and conjunctival injection. These lead to conjunctivitis, sclerosing keratitis, uveitis glaucoma, cataract and less commonly, choroiditis and optic neuritis.
The finding of nodules or characteristic lesions of the skin or eyes in a patient from an endemic area, associated with eosinophilia is suggestive. Skin snips or shavings, taken with a corneoscleral pouch or scalpel blade from calf, buttock and shoulder, are placed in saline under a cover slip on a microscope slide and examined after 4 hours. Microfilariae are seen wriggling free in all but the lightest infections. Slit lamp examination may reveal microfilariae moving in the anterior chamber of the eye or trapped in the cornea. A nodule may be removed and incised, showing the coiled, thread-like adult worm.
Causes and prevention of onchocerciasis
Onchocerciasis is the result of infection by the worm 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 microfilariea, which mature into the infective larva and are transmitted to a new host in subsequent bites.
Prevention: Mass treatment with ivermectin is practiced. It reduces morbidity in the community and prevents eye disease from getting worse. Simulium can be destroyed in its larval stage by the application of insecticide to streams. Long trousers, skirts and sleeves discourage the fly from biting.
Hydrocele, femoral hernias and scrotal elephantiasis can occur. Eye complications can lead to blindness.
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- 30mg may be given daily for 2 or 3 days. Eradication of Wolbachia with doxycycline (100mg daily for 6 weeks) prevents reproduction of the worm.