ONCHOCERCIASIS

Onchocerciasis or river blindness is a chronic infection of the skin and the
eyes by the filaria Onchocercus volvulus. It is transmitted by female
blackflies which are typically found near fast moving water. People living
in these areas get infected again and again, thereby accumulating
hundreds to thousands of microfilariae in the skin and the eyes, where
they move around freely. In the skin this causes severe itch as the major
presenting complaint. In the first stages there are only a few erythematous
hyperpigmented papules and scratch marks. Later the whole skin
thickens and becomes dry and lichenified. There is loss of elasticity
(hanging groins). Skin hyper-, hypo- and depigmentation may occur in
chronic cases. Onchonodules, which represent the adult worms, can be
seen and palpated, in particular above the hipbones but also elsewhere.
Biopsy or skin snip may show microfilariae. Eye involvement is a well
known cause of blindness.
If the history is suspect but microfilariae have not been demonstrated a
Mazotti test can be performed. Under careful conditions (cave:
anaphylactic shock) 50-100 mg diethylcarbamazepine (DEC, Hetrazan) is
given. A positive test yields intolerable itch within a few hours.
Management of onchocerciasis
- Treat secondary infection with antiseptics or antibiotics as impetigo and secondary
lichenified eczema as lichen simplex.
- Ivermectin kills microfilariae with a single oral dose. The adult worms are not
affected however. A patient staying in an endemic area will therefore need repeated
treatment every 3 to 12 months depending on the amount of itching. If the patient
moves out of the endemic area repeated treatment may cure the infection as the
adult worms will die after a few
years.
-When there is eye involvement
steroid treatment should preceed
ivermectin.
- Single dose of ivermectin (6 mg
tablets) according to body weight in
kilograms: under 30 kg: 0,5 tablet,
30 to 50 kg: 1 tablet, 50 to 70 kg: 1,5
tablet, over 70 kg: 2 tablets.