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Pathologic changes of human onchocerciasis: implications for future research
Abstract:
Onchocerciasis--infection by Onchocerca volvulus--has four cardinal manifestations: dermatitis, subcutaneous nodules, sclerosing lymphadenitis, and eye disease. The first three are discussed here. The dermatitis begins when microfilariae degenerate in the dermis. This process is accompanied by inflammation, with degranulation of eosinophils and deposition of the major basic protein of the eosinophil granules on the cuticle of the microfilariae. So far as is known, the chronic effects of onchocerciasis are all a consequence of the degeneration of microfilariae. Subcutaneous nodules contain coiled adult worms and have an outer layer of fibrous scar and a central inflammatory cell exudate, which may cavitate. Perfusion of India ink reveals arborization of capillaries around adult worms, which derive nutrition from these networks. Onchocercal lymphadenitis is characterized initially by histiocytic hyperplasia and follicular atrophy and later by fibrosis and obstruction of lymph flow, a condition causing adenolymphocele ("hanging groin") and elephantiasis of the genitalia. Some patients appear to have immune tolerance to degenerating microfilariae, perhaps as a result of exposure in utero to microfilarial antigens in the maternal circulation. In contrast, other patients (Yemenites, for example) have a localized but intense response to a few microfilariae; these patients are hypersensitive--perhaps because they were not exposed to microfilarial antigens in utero. Autopsy data on infection of deep organs are limited.
Insights
Onchocerciasis, caused by Onchocerca volvulus, leads to skin, nodule, and lymph node disease. Chronic effects stem from microfilariae degeneration, impacting various tissues and immune responses.
Area of Science:
- Tropical medicine
- Parasitology
- Immunology
Background:
- Onchocerciasis, or river blindness, is caused by the parasitic worm Onchocerca volvulus.
- The infection presents with dermatitis, subcutaneous nodules, sclerosing lymphadenitis, and eye disease.
Purpose of the Study:
- To describe the pathological manifestations of onchocerciasis, focusing on skin, nodules, and lymphadenitis.
- To explore the underlying mechanisms of inflammation and immune responses in affected individuals.
Main Methods:
- Pathological examination of affected tissues (dermis, subcutaneous nodules, lymph nodes).
- Histological analysis of inflammatory cell infiltration and tissue changes.
- Review of clinical presentations and immune responses in different patient groups.
Main Results:
- Dermatitis results from degenerating microfilariae, triggering eosinophilic inflammation.
- Subcutaneous nodules contain adult worms surrounded by fibrous tissue and capillaries.
- Lymphadenitis progresses from hyperplasia to fibrosis, causing lymph flow obstruction and conditions like "hanging groin" and genital elephantiasis.
Conclusions:
- Chronic onchocerciasis pathology is primarily driven by microfilariae degeneration.
- Immune tolerance and hypersensitivity to microfilariae vary among individuals, potentially linked to in utero exposure.
- Understanding these mechanisms is crucial for managing onchocerciasis complications.