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Query: UMLS:C0042961 (volvulus)
 4,305 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Onchocerciasis is a major cause of blindness worldwide, and much of the blindness is caused by onchocercal chorioretinitis. In an experimental animal model for ocular onchocerciasis, intravitreal injections of 10,000 live Onchocerca volvulus microfilariae isolated from infected humans into the eyes of cynomolgus monkeys (Macaca fascicularis) resulted in patchy, progressive loss of retinal pigment with pigment clumping. Areas of pigment loss were less extensive in animals that had been sensitized with microfilariae. Intravitreal injections of dead O. volvulus microfilariae resulted in mild vitritis with relatively less clinical change noted in the retina and choroid. Histopathologic examination revealed thinning and loss of outer retinal layers with pigment migration into the retina, and inflammation was more pronounced in eyes that received live microfilariae. Clinical changes appeared in eyes receiving live microfilariae before the development of significant antibody or cell-mediated immune responses. O. volvulus microfilariae appear to be more suitable than O. lienalis microfilariae in producing lesions which resemble human onchocerciasis in the primate model.
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PMID:Experimental ocular onchocerciasis in cynomolgus monkeys. IV. Chorioretinitis elicited by Onchocerca volvulus microfilariae. 201 31

Autoimmune mechanisms are thought to play a role in the pathogenesis of the chorioretinal changes in ocular onchocerciasis. In this study, the involvement of autoimmunity against retinal antigens in developing chorioretinitis was investigated. Serum levels of autoantibodies, directed against human S-antigen and interphotoreceptor retinoid-binding protein (IRBP), were determined in patients with onchocerciasis (n = 46) and endemic controls (n = 38) from Sierra Leone with the use of an enzyme immunoassay. In both groups high levels of anti-human S-antigen and IRBP antibodies were detected. No relationship could be demonstrated between the antiretinal antibody level and the occurrence of chorioretinitis in onchocerciasis. The levels of both anti-human S-antigen and IRBP antibodies were significantly higher in patients with onchocerciasis compared with endemic controls (P less than 0.001). Cross-reactivity of antiretinal antibodies with parasitic antigens could not be demonstrated as a possible explanation for the higher levels in patients with onchocerciasis. No correlation was found between the levels of antibodies of different classes against the crude Onchocerca volvulus, the egg antigen, or the microfilariae and the antiretinal antibody levels. Furthermore, in a panel of 13 different monoclonal antibodies directed against O. volvulus, only one showed a slight anti-human IRBP reactivity and none reacted with S-antigen. The immune response against the two retinal antigens investigated was not specific for onchocerciasis because high antibody levels were also found in patients with Bancroftian filariasis from Papua, New Guinea, and Surinam.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Humoral autoimmune response against S-antigen and IRBP in ocular onchocerciasis. 236 68

Parasitological and clinical observations were made on residents of Pongo Nuer, a village in the province of Bahr El Ghazal, southwestern Sudan. Of 202 skin biopsies, 189 (94%) were positive for microfilariae of Onchocerca volvulus. Nodules were most common around the pelvic girdle and rare on the limbs or head. Microfilarial intensities, ranging up to 1,094 mf/mg of skin, were highest at the iliac crest and shoulder; they increased rapidly in childhood but then appeared to reach a plateau maintained through adult life. Nodule presence and number, especially at multiple sites, was significantly related to skin microfilarial intensity. Dermal manifestations of O. volvulus infection were widespread and severe, ranging from acute maculopapular eruptions to chronic, diffuse, and degenerative changes, even in young adults. However, high skin microfilarial intensities were found in asymptomatic individuals; conversely, lowest intensities were in those with severest maculopapular lesions, suggesting that host response was a major determinant of disease outcome. Microfilariae were detected in the cornea or anterior chamber of the eyes of one third of those examined in all age groups, but lesions of the posterior segment, including optic neuritis, chorioretinitis, and pigmentary abnormalities, were considered responsible for visual deficits in the population sample. Some pathologic changes in the anterior segment attributable to microfilariae were more common in the young than in adults but there was no preponderance of sclerosing keratitis in adults, contrary to expectations in hyperexposed individuals in a Sudan savannah zone. The best correlate of the presence of microfilariae in the eye was the intensity of infection in shoulder skin snips. Little value could be derived from data on outer canthus samples, either in terms of severity of ocular infection or disease. Microfilaremia was common (76%) but in only one case was attributed to O. volvulus; the remainder were due to Mansonella perstans.
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PMID:Onchocerciasis in southwestern Sudan: parasitological and clinical characteristics. 382 96

Diethylcarbamazine (DEC) therapy for Onchocerca volvulus infection results in frequent ocular and systemic complications, but the pathogenesis of these complications is unclear. Twenty men with O. volvulus infection were treated over a period of six months with DEC given daily for one week and weekly thereafter. Major systemic and ocular complications included proteinuria, severe pruritus, visual field constriction, optic nerve pallor, chorioretinitis, anterior uveitis, and punctate keratitis. Levels of circulating immune complexes (CICs) were increased (greater than 11% [125I]C1q binding) in 14 of the 20 men prior to treatment. Persons with pretreatment C1q binding activity of greater than 30% were at increased risk to develop constriction of visual fields (P less than 0.05) and proteinuria (P less than 0.015). Linear regression analysis revealed a striking correlation between pretreatment levels of CICs and the total number of both systemic and ocular complications (P less than 0.001) and ocular complications alone (P less than 0.005). These results suggest that CICs may be important in the pathogenesis of the delayed systemic and ocular complications following DEC therapy for O. volvulus infection.
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PMID:Ocular and systemic complications of diethylcarbamazine therapy for onchocerciasis: association with circulating immune complexes. 684 23

A sample of 76 persons in a hyperendemic village of onchocerciasis in the rain forest of Liberia was examined ophthalmologically. A reduced visual acuity of less than 6/18 was found in nearly 10%. Punctate keratitis was observed in 36%, microfilariae in the anterior chamber in 46%, proliferative chorioretinitis in 4% and optic atrophy in one person. The overall frequency of ocular onchocerciasis was 62%, but the severity of findings in most individuals was very minimal. The occurrence of microfilariae in the anterior chamber was positively correlated with microfilarial densities in the skin of the hip, outer canthus and blood and the burden of adult O. volvulus isolated from extirpated onchocercomata.
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PMID:Ocular onchocerciasis in a hyperendemic village in the rain forest of Liberia. 723 47

Travelers to West, central and eastern Africa as well as to selected areas of Latin America are at risk for infection with Onchocerca volvulus. Infection with this tissue nematode may cause chorioretinitis and keratitis, and it is responsible in endemic areas for blindness in millions.1 In addition to ocular manifestations, it can produce a distressing pruriginous dermatitis or subcutaneous nodules. Clinical manifestations vary according to the parasitic load, previous immunity, and duration of infection.1 Infection is initiated by inoculation with larvae during the bite of the Simulium black fly. Once in the connective tissue, larvae mature to filiform adults and may remain in tissues for years, with the clinical manifestations being produced by the inflammatory reaction to dying parasites. Female adults produce large amounts of microfilaria that migrate through skin and connective tissue; once an infected host is bitten, the infectious larvae develop again in the female Simulium black fly and the life cycle is completed. Transmission is from person to person, and may occur even after a relatively short exposure.2 Although infection of travelers with O. volvulus is rare, according to the Centers for Disease Control and Prevention, 46 new cases of onchocerciasis were diagnosed in the United States in 1994 (Dr. David Addis, personal communication, June 1996). We describe the case of an expatriate who became infected with O. volvulus and we review the treatment and recommendations for prevention of this parasitic infection.
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PMID:Onchocerciasis in an expatriate living in Cameroon. 981 71

In many parts of the world, parasitic infections of the eye are a major cause of blindness. The parasites Toxocara canis, Onchocerca volvulus, Taenia solium, Ancylostoma caninum, and Cysticercus celulosae all have been responsible for blinding ocular infections. The nematodes T. canis and Toxocara cati are parasitic roundworms that infect dogs (toxocarosis), other canidae, and cats. Ocular toxocariasis is an uncommon worldwide infection caused by the nematode larvae of T. canis, commonly found in dogs. Human transmission is usually via geophagia, the ingestion of food contaminated with Toxocara eggs, or contact with infected puppies, often resulting in devastating ocular or systemic effects. Ocular toxocariasis is typically a monocular disease of young children, and its clinical findings include posterior and peripheral retinochoroiditis, optic papillitis, and endophthalmitis. The inflammatory response created by ocular involvement may result in epiretinal membrane formation, traction retinal detachment, and combined traction-rhegmatogenous retinal detachment. Diffuse unilateral subacute neuroretinitis is another ocular parasitic infection that usually results in severe visual loss. Evidence suggests that diffuse unilateral subacute neuroretinitis is caused by a solitary unidentified nematode of two different sizes, but to date, only a small number of nematodes have been recovered from eyes affected with the infection. Diffuse unilateral subacute neuroretinitis occasionally can affect the fellow eye.
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PMID:Nematode infections of the eye: toxocariasis and diffuse unilateral subacute neuroretinitis. 1173 85

Onchocerciasis is caused by the parasitic worm Onchocerca volvulus, which releases millions of offspring (microfilariae). Microfilariae migrate through the skin and can enter the anterior or posterior regions of the eye. While alive, the microfilariae appear to cause little or no inflammation, being in the anterior chamber. However, when they die, either by natural attrition or after chemotherapy, the host response to degenerating worms can result in ocular inflammation (keratitis, uveitis, chorioretinitis, neuritis of the optic nerve) that causes progressive loss of vision and ultimately leads to blindness. With the use of a mouse model of corneal inflammation to study the pathogenesis of ocular onchocerciasis by injecting worm extracts directly into the corneal stroma, it was found that worms treated with the antibiotic doxycycline, which destroys Wolbachia, induced lower corneal stromal thickness and stromal haze (indicators of corneal oedema and opacity) and neutrophil infiltration compared with both untreated worms and worms that do not harbour Wolbachia. These data indicate that endosymbiotic Wolbachia bacteria in filarial parasites have a key role in the pathogenesis of river blindness. Worms recovered from patients treated for 6 weeks with doxycycline contained fewer Wolbachia bacteria and had abnormal embryogenesis, indicating a role for Wolbachia in the survival or fecundity of the worms. Antibiotic treatment may also reduce the severity of the inflammatory response in the cornea.
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PMID:[Ocular onchocerciasis: a key role for Wolbachia]. 1797 45