ONCHOCERCIASIS (River Blindness) / MedUrgent

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ONCHOCERCIASIS (River Blindness)




Onchocerciasis is a filarial disease caused by the filarial nematode Onchocerca volvulus which is transmitted by the black fly Simulium. The Disease  presents with dermatitis, eye lesions and subcutaneous nodules. Adult females are 30 to 50 cm long while adult male worms are only 2-4 cm long. Microfilariae are 2 - 3 mm long. The vector Simulium damnosum develops in fast flowing streams and rivers and can travel for very long distances. Microfilaria, transmitted to man by a simulium bite, stay in the subcutaneous tissue for up to two years to develop into adult worm. After the male and female adults copulate, millions of microfilariae are produced by the female and they tend to concentrate in the skin, eyes and lymph nodes. In the skin, larvae mature in 2-4 months and can live up to 17 years in small colonies in the subcutaneous and connective tissue. Adult worms form nodules while microfilariae migrate through tissues provoking inflammatory lesions that heal with scars.







CLINCAL PICTURE 

The incubation period is long and the first clinical sign may appear months or years after infection. The first sign is usually itching which is localized and later becomes generalized. Superficial lymph nodes may enlarge and hang down in folds of loose skin like that of the groin forming "hanging groin". Hydrocoele, fermoral herniae and scrotal elephantiasis may occur. Eye disease (onchophthalmia) is associated with chronic heavy infections. Infections of the anterior chamber and the cornea may lead to opacities: punctuate keratitis, chorioretinits and retinal atrophy. 

Nodules: 

Nodules are found in the deep dermis and subcutaneous tissue especially over bony prominences e.g. superior iliac spine, iliac crest, trochanter, sacrum, coccyx, ribs, elbows and knees. Adult worms are coiled inside these nodules.

Subcutaneous lesions:

Two reactions are provoked by the degeneration of microfilariae, viz. local inflammatory process with eosinophilic infiltration and the granuloma formation. These inflammatory changes lead to fibrosis, dilatation of lymphatics, enlargement of lymph nodes and tortuosity of blood vessels and consequently sclerosis and edema of the affected site or limb. Scarring in lymph nodes leads to obstruction of lymph flow ending in lymphoedema (elephantiasis and hanging groins). Dermatitis is associated with severe itching over the trunk, pelvis, buttocks and thighs. There is residual hypopigmentation, hyperpigmentation, scar and wrinkle formation. 

Ocular lesions:

Live microfilariae invade the eyes and their death provokes severe reactions leading to corneal opacities, sclerosing keratitis, uveitis, posterior Synechiae, secondary cataracts, glaucoma and choriodoretinitis. Other rare complications include dwarfism, epilepsy and arthritis. 





Investigations 

•Superficial skin snip for microfilariae from the buttock. calf and shoulder

• Excision biopsy and microscopy of nodules to identify adult worms

• Slit lamp examination of the eyes for microfilariae 

• Eosinophillia is a permanent feature

• Serology: CFT, HAT, IFFT, ELISA 

• Mazzotti test: give the suspected patient 25 - 50 mg DEC. infected patient will develop intense pruritus within a few hours and continues for 2-3  days. Sometimes it is associated with  systemic manifestations e.g. fever, malaise, swollen and tender lymph nodes facial eosinophilia. Care must be taken because the reaction can be very severe.


TREATMENT

1- Diethyl carbamazine (DEC): Start with a dose of 1mg/kg/day and increase gradually up to 5-6 mg/kg/day for 21 days. Antihistamine and corticosteroids may be added to reduce the Mazzotti reaction that may follow (the heavier the infection, the more severe is the reaction).

2- Suramin: Start with a small dose of 10% solution i.v. (50-100 mg) and increase the dose weekly for 6 weeks. It may be given after completing the course of DEC

3- Combined therapy with Metronidazole plus levamisole. However, DEC and Suramine are no longer recommended for the treatment of Onchocerciasis because of their severe adverse reactions.

4-Ivermectin: This is now the drug of choice. It is given as a single dose of 100-200 ug/ kg. It kills the microfilaria and prevents infection for 9 months. Ivermectin should be avoided in persons with heavy loa loa infection, pregnancy, infants less than one week old and children shorter than 90 cm

Nodulectomy: This is done as an adjunct to chemotherapy especially nodules that are situated near the eyes.

Doxycycline: To treat Wollbachia and thus sterilizing the adult worm. The dose is 100 - 200 mg /day for 4-6 weeks. Doxycycline does not affect the microfilaria. It is advisable to use one or two doses of Ivermectin to eradicate the microfila.

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