Onchocerciasis is a helminthic invasion from the group of filariatoses, leading to damage to the skin, lymph nodes and eyes. Dermatological changes in onchocerciasis are characterized by the formation of dense fibrous nodes, itchy rash, slowly healing ulcers, depigmentation sites. The defeat of the lymphatic system is accompanied by sclerosis of lymph nodes, the development of lymphedema. The lesion of the eyes proceeds according to the type of chronic conjunctivitis, keratitis, complicated by cataracts, glaucoma, chorioretinitis. The diagnosis of onchocerciasis is confirmed by the detection of pathogen larvae in a skin biopsy. Specific therapy of onchocerciasis is carried out with antiparasitic drugs with micro- and macrophilaricidal action.
ICD 10
B73 Onchocerciasis
General information
Onchocerciasis is a transmissible helminthiasis caused by parasitization of nematodes Onchocerca in the human body. Onchocerciasis mainly affects the lymphatic system, skin, subcutaneous tissue and the organ of vision (“river blindness”). Foci of onchocerciasis and other filariasis have been identified in Africa, Latin America, and the Middle East. In total, there are about 18 million patients with onchocerciasis in endemic countries. Onchocerciasis and its complications are one of the leading causes of blindness, second in frequency to cataract and trachoma. The features of parasitization of the pathogen in the human body make onchocerciasis an urgent disease for infectious diseases, dermatology and ophthalmology.
Causes
Parasitic helminths that cause onchocerciasis – nematodes Onchocerca volvulus, belong to the family Filariidae, suborder Filariata. Onchocerci are filamentous roundworms with thinner ends. The sizes of adult parasites (macrofilariae) are 19-50 mm long, 0.13-0.4 mm wide (females are larger than males); the sizes of larvae (microfilariae) are 0.15-0.37 and 0.05-0.09 mm, respectively.
The only source of invasion and the final host of helminths is a person with onchocerciasis. Intermediate hosts and at the same time carriers-distributors of onchocerciasis are blood-sucking midges Simulium, living near rivers and reservoirs. During the bite of a sick person, larvae enter the body of midges, which become invasive after 6-12 days. With repeated bites of people, the larvae penetrate into the skin, migrate through the lymphatic system, penetrate into subcutaneous fat, where they turn into sexually mature individuals. Adult Onchocerci parasitize in subcutaneous nodes (onchocercomas), where they hatch microfilariae larvae. Larval individuals can penetrate the lymph nodes and eyes; their life expectancy is 6-30 months. Adult Onchocerci live up to 10-15 years, producing up to 1 million annually. larvae.
Onchocerciasis mainly affects rural residents of endemic areas located near rivers, in places where midges hatch. The age limits of helminthic invasion have not been determined; children and the elderly are equally susceptible to infection with onchocerciasis. In the pathogenesis of onchocerciasis, the main role belongs to the sensitization of the body by microfilariae antigens and their waste products, which is accompanied by local and general allergic reactions. Parasitizing in the skin, microfilariae cause the so-called onchocercous dermatitis, characterized by depigmentation, thickening of the epidermis, formation of onchocercomas, ulceration. When entering the eyes, the larvae of the parasite cause damage to the vascular membrane of the eye, retina and optic nerve, threatening blindness. When the lymphatic system is affected, chronic lymphostasis, lymphadenopathy occurs.
Onchocerciasis symptoms
The first clinical signs of onchocerciasis develop about a year after infection. They include fever, general malaise, and blood eosinophilia. Onchocercous dermatitis is accompanied by intense itching of the skin (filarial scabies), dryness and peeling of the skin, the appearance of hyperpigmentation. The appearance of papular rash is characteristic, the elements of which can transform into pustules, ulcers and heal for a long time with the formation of scars. Exacerbations of dermatitis resemble erysipelas of the skin.
With a significant invasion of microfilariae, the skin loses elasticity, becomes hypertrophied and becomes like an orange peel (“elephant skin”, “crocodile skin”). A prolonged course of onchocerciasis leads to persistent depigmentation of the skin (“leopard skin”), which often occurs on the lower extremities, in the axillary and inguinal areas, on the genitals. The outcome of onchodermatitis is atrophy of the epidermis, hair follicles and sweat glands. In the advanced stage of onchocerciasis, large hanging folds of skin are formed (“lion face”, “Hottentot apron”, “hanging groin”, “hanging armpit”), inguinal and femoral hernias often occur.
A typical manifestation of onchocerciasis is the formation of onchocerci – fibrous subcutaneous nodes ranging in size from 0.5 to 10 cm, dense and painful to the touch. More often, onchocercomas are localized in the head, pelvis, shoulder blades; with the formation of nodes around the joints, the development of tendovaginitis and arthritis is noted. The defeat of the lymphatic system in onchocerciasis is characterized by an increase in lymph nodes (especially femoral and inguinal), their sclerosis, the development of lymphostasis (elephantiasis) of the scrotum and lower extremities.
The most dangerous manifestations of onchocerciasis occur during the migration of microfilariae into the membranes and media of the eye. In the initial period, due to mechanical and toxic-allergic effects, signs of conjunctivitis develop: lacrimation, photophobia, pain in the eyes, swelling and hyperemia of the conjunctiva. Corneal lesion is accompanied by spot keratitis, “snow opacification” of the cornea of the eye, ulcers and corneal cysts. Iridocyclitis, atrophy and depigmentation of the iris often occur. Eye damage in onchocerciasis is complicated by cataracts, glaucoma, chorioretinitis, optic nerve atrophy and blindness.
Diagnosis and treatment
Onchocerciasis is supported by the presence of specific dermatitis, onchocercomas, eye lesions and changes in the lymphatic system, as well as an appropriate epidemiological history. The diagnosis is confirmed by the detection of onchocerci in excised subcutaneous nodes or microfilariae in thin sections or biopsies of the skin. In addition, microfilariae can be detected in the cornea, anterior and posterior chamber of the eye during biomicroscopy. To assess the degree of eye damage, the patient needs an ophthalmologist’s consultation. Serological methods (ELISA), intradermal allergic test are used in the diagnosis of onchocerciasis. Laboratory and instrumental diagnostics allows differentiating onchocerciasis from other filariasis, fungal skin diseases, leprosy, hypovitaminosis A and B.
For the treatment of onchocerciasis, several schemes have been developed, the appointment of which is carried out individually only by specially trained parasitologists. This is due to the toxicity of the drugs, as well as the possibility of severe toxic-allergic reactions caused by the death of parasites. For the treatment of onchocerciasis, drugs with microfilaricidal (diethylcarbamazine, ivermectin) and macrofilaricidal (suramin, trimelarsan) action are used. With severe allergic reactions, antihistamines, corticosteroids, plasmapheresis are prescribed. Onchocercous nodes located on the head are subject to surgical removal; opening and drainage of abscesses is carried out according to generally accepted rules.
Measures to protect against infection with onchocerciasis are reduced to individual protection from midge bites (wearing protective clothing, using repellents), insecticidal treatment of insect spawning sites. In regions endemic to onchocerciasis, chemoprophylaxis with ivermectin is possible.