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  4. the cause of onchocerciasis, what are the causes of onchocerciasis

the cause of onchocerciasis, what are the causes of onchocerciasis

the cause of onchocerciasis, what are the causes of onchocerciasis

The main cause of onchocerciasis: Onchocercia circulans parasites on human skin, subcutaneous tissue and eyes

1. Causes of disease

Adults are linear, white, tapered and blunt at both ends. The size of female and male worms are 33.5-50mm*0.27-0.40mm and 19-42mm*0.13-0.21mm, respectively. Microfilaria are highly mobile and have no sheath. Microfilaria has two sizes, the larger one is long and wide (285~368)μm*(6-9)μm; the smaller one is long and wide (150~287)μm*(5~7)μm. When the intermediate host gnat (Simulium) bites a person, the microfilaria enters the gnat and develops into an infected larva. When the gnat bites a person again, the larva enters the human body through the bite wound and infects the person. The larvae develop into adults for about one year, and they can become ill after a one-year incubation period. The adult lifespan is generally 8-10 years, and some can last as long as 15 years.

2. Pathogenesis

The main effects of Onchocerciasis on the body are mechanical stimulation and toxic stimulation. The secretion of microfilaria or toxic stimulus after death can cause inflammation and tissue lesions at the infected site.

3. Pathophysiology

Pathological examination revealed granulomatous tissue, fibrous tissue and infiltration of eosinophils, giant cells, and plasma cells around the parasite. Ocular tissues often have chronic non-granulomatous inflammatory changes. Manifestations include tearing, photophobia, keratitis or corneal opacity, pupil deformation, iritis or iridocyclitis, chorioretinitis, optic nerve atrophy, and finally blindness. Skin tissue cell infiltration, inflammation, fibrotic lesions, subcutaneous nodules, abnormal pigmentation, and later skin thickening and atrophy. Lymph node lesions are mainly chronic inflammatory changes.


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