Onchocerciasis B73

O'Neill in 1875; Blacklock in 1927;

Chronic form of filariasis (river blindness) caused by Onchocerca volvulus. The worm larvae are transmitted by black flies and lead to skin and eye infestation with formation of subcutaneous nodules (onchocerciasis, onchocerciasis nodules, onchocercomata).

• Localized form: Sowda.
• Generalized form: Onchodermatitis, eye changes (river blindness).

Endemically widespread in 30 countries of tropical sub-Saharan Africa ("African onchocerciasis belt" between Senegal and Ethiopia), more rarely in Central and South America, Yemen and Saudi Arabia. Approximately 85 million people worldwide live in endemic areas and are thus threatened by this infection.

Prevalence (worldwide): 37 million people (WHO data); with skin involvement: 4 million people; with eye involvement (e.g. photophobia, blindness, visual impairment): 2 million people.

Infection with nematodes in larval stage L3. Transmission by the fly-like black flies of the genus Simulium (habitat: flowing waters). In the course of 12-20 months, seperate sex adult worms develop, which can live up to 15 years and collect in subcutaneous nodes (onchocercomata). These nodules can contain 1 to 40 worms and can be up to 3.0 cm in diameter.

Adult worms become 2.0-8.0 cm (male forms) and 15-20-50 cm (female forms) long. Female filariae can live up to 15 years and produce 500-700 microfilariae (approx. 0.3 mm long) daily, migrate from the nodes and live for 6-18 months in the skin and subcutis. The onchocerciasis itself does not cause any symptoms. Problems are caused by the dermal microfilariae which are present in large quantities (the microfilariae loads are often >100/mg skin). They lead to the different types of onchocerciasis. forms of onchodermatitis.

The microfilariae are ingested by a mosquito during a blood meal and develop there in the thoracic muscles of the insect into the infectious larvae within 6-10 days.

Onchocercomata (Onchocerciasis nodules; Onchocercomata): In Africa: Predominantly over the iliac crest, at the femoral trochanter or sacrum, more rarely occurring in the thoracic wall. In Central America > 50% of the nodes are located on the head or thorax.

Onchodermatitis: The whole integument may be affected. Leopard skin occurs mainly on the shins. Erisipelas de la costa (in Central America): Erythema and oedema (with fever) localized in the facial skin.

• Integument:
  • Onchocercomata (Onchocerciasis nodules; Onchocercomata): Painless, subcutaneously located, parasitic, movable, firm nodules, about 0.5-10 cm in diameter, partly baked into conglomerates. Predilection sites: knee, iliac crest, trochanter, os sacrum, thorax, head)
  • Onchodermatitis: may include pruritus, pigmentary changes, itchy papules (craw craw; gale filarienne), peau d'orange (swelling), lizard skin (dry, scaly dermatitis in a mosaic pattern), leopard skin (patchy depigmentation), hanging groin (loss of elasticity), erisipelas de la costa (Central America: erythema and oedema of the facial skin with fever), occasionally elephantiasis and hydrocele.
  • Sowda (chronic hyperreactive onchodermatitis): localized maculo-papular dermatitis with regional swelling of the lymph nodes.
• Eye involvement:
  • Keratitis, iritis, retinitis, optic atrophy, corneal opacity with blindness due to the migration of microfilariae into the eye.

Detection of microfilariae in skin or eyes:

• superficial curettage of skin lesions (skin snip): samples are examined for microfilariae under the microscope in common salt. Disadvantage: Negative result in case of early or latent disease (detection not earlier than 10 months after infection).
• Immunodiagnosis: No distinction between past or acute infection possible. High sensitivity, but low specificity (cross-reactions with other helminth antigens)
• PCR: detection of the repetitive DNA sequence 0-150, which only occurs in O. volvulus (high sensitivity).
• Mazotti patch test: contact allergic skin reaction after topical application of diethylcarbamazine (1.6% solution) in the presence of microfilariae (high sensitivity and high specificity). Alternative therapy test with 50 mg diethylcarbamazine (Hetrazan): results in itchy papules after 24 hours (unreliable due to lack of identifiability of patients with slight manifestation).
• Eosinophilic kinetics: in combination with Mazotti reaction: reduction of eosinophils after DEC administration, significant increase again after 2-14 days
• Furthermore: slit lamp examination of the eye (in case of infestation of the eye microfilariae can be seen by means of a slit lamp).

The treatment is usually lengthy, as adult worms are difficult to reach with medication. Microfilariae are reproduced in this way within a few months after therapy. Monitoring of the eyes to prevent blindness.

Note: systemic therapy may be accompanied by a severe general reaction(Mazzotti reaction) caused by the sudden decay of the worms.

• Ivermectin: (1st choice therapy; [e.g. Mectizan, only available through the international pharmacy]): 1 time 150-200 μg/kg KG p.o. at the beginning and in the month 5 or 6 after first dose (blood count and transaminase control required!). Ivermectin reduces dermal microfilariae. However, Ivermectin shows no effect against adult worms. The active substance is much better tolerated than the alternative preparations diethylcarbamazine or suramin. With a single dose of 150-200 μg/kg KG the microfilariae concentration in the skin decreases rapidly. Treatment over years at the stated dose in intervals of a few months up to once a year (depending on the renewed increase in the number of microfilariae) is usually necessary until the macrofilariae are finally destroyed. The response rate to adult worms is less good. Regular control of the vitality of adult worms is therefore important. Excision if possible.
• Doxycycline: Important for the new chemotherapy approaches is the presence of endosymbionts of the genus Wolbachia in the worms. These obligatory intracellular bacteria are important for fertility and survival of the worms. A 6-week therapy with 100 mg doxycycline/day p.o. leads to long-term worm sterility. The infertile worms die after 18-20 months. It is recommended that doxycycline therapy be carried out first and then treatment with ivermectin (see above). This procedure reduces the severe immunological reactions that occur during the initial therapy with ivermectin or diethylcarbamazine.
• Diethylcarbamazine (e.g. Hetrazan) also acts predominantly on microfilariae and shows no advantages in efficacy over ivermectin with a considerably higher rate of side effects. Gradual dosage: 0.5 mg/kg bw p.o. on day 1, increase to 2.0 mg/kg bw on day 2 and 3, then 2 times/day 2.0-2.5 mg/kg bw on the following days. Usual long-term dosage: 3 times/day 2.0 mg/kg bw over 3-4 weeks. The NW(Mazzotti reaction) can be reduced by prophylactic administration of glucocorticoids such as prednisone (e.g. Decortin) 60-80 mg/day 2 days before DEC therapy; balance out quickly. If there are still living adult worms that cannot be removed surgically or if there is a risk of blindness, a 6-week treatment with Suramin is carried out.
• Suramin: (e.g. Germanin, Naphoride) is due to its toxic NW only used today in cases of acute risk of blindness caused by macrofilariae. The preparation should be avoided in patients with previous illnesses such as kidney damage or poor general condition. Initial injection of 2 mg/kg bw (max. 100 mg) Suramin slowly i.v. to exclude a Mazzotti reaction. Subsequent dosage over 6 weeks as follows:
  • 1st week: 3.3 mg/kg bw/week.
  • 2nd week: 6.7 mg/kg bw/week.
  • 3rd week: 10.0 mg/kg bw/week.
  • 4th week: 13,3 mg/kg bw/week.
  • 5th week: 16,7 mg/kg bw/week.
  • 6th week: 16,7 mg/kg w/w.

  • Notice! Adults > 60 kg bw max. 4 g, attention must be paid to toxicity.

Diagnosis and therapy should be left to experienced tropical physicians.

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