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

Two species of Nearctic black fly, Simulium decorum and S. pictipes, exhibit partial susceptibility to infection with the bovine parasite, Onchocerca lienalis, when inoculated intrathoracically with microfilariae. In addition, a proportion of S. decorum females will support the development of the human parasite, O. volvulus, to the third larvae stage. Infection rates with second- or third-stage larvae seven or more days after varied among geographic strains of S. decorum, ranging from 6.5% in a strain from northern New York State to 48.7% in a strain from Georgia. The average number of larvae per infected female ranged from 1.00 to 1.78 in the three strains examined. Partial susceptibility to O. lienalis was found to persist in colonized strains of s. decorum, and cryopreserved microfilariae of this parasite retained their infectivity. Seven or more days after inoculation with microfilariae of the Guatemalan strain of O. volvulus, 16.7% of the females of S. decorum harbored second- or third-stage larvae. Development of O. lienalis and O. volvulus proceeded normally in these black flies, and moderate increases in susceptibility rate and number of infective larvae were noted in response to increased microfilarial dosages.
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PMID:The development of Onchocerca spp. in Simulium decorum Walker and Simulium pictipes Hagen. 723 46

Onchocerciasis is commonly known as River Blindness and affects about 18 million people around the world. It is transmitted by black flies that breed in river and stream rapids and transmit the parasitic microfilariae, Onchocerca volvulus, to people who live and work near such rivers. Infection with the microfilariae results in blindness or visual impairment for 1 or 2 million people. The microfilariae migrate to superficial tissues and may invade any part of the eye and ocular structure. Living worms cause little damage, however, their death triggers a localized inflammation which can lead to blindness. Sclerosing keratitis, a severe corneal involvement, is the major cause of blindness from the disease. The World Health Organization (WHO) Expert Committee on Onchocerciasis has estimated that 9% of the disease is found in Africa, the rest occur in Yemen and Latin America. Treatment with ivermectin is contraindicated for pregnant and lactating women, children under 5 years of age, asthmatics, and people with other diseases. The WHO Onchocerciasis Control Program in 11 countries of West Africa has eliminated the risk of onchocerciasis by aerial spraying of black fly breeding sites only from 1 country. A single annual oral dose (150 mg/kg) of ivermectin can reverse early lesions in the cornea. Ivermectin must be taken annually to sustain protection against blindness, thus its incorporation into primary health care along with malaria, AIDS, trachoma, xerophthalmia, and cataract is most cost effective. Nigeria and Tanzania have optometry schools, and optometrists can play a significant role in onchocerciasis control and blindness prevention programs by training local health care workers to distribute invermectin in vision screening programs.
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PMID:Onchocerciasis and other eye problems in developing countries: a challenge for optometrists. 824 90

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

Infections with Dracunculus medinensis frequently occur in the same geographical area as infections with Onchocerca volvulus and Wuchereria bancrofti. This study analysed the significance of D. medinensis infections for the specificity and sensitivity of available tests for antibody-based diagnosis of onchocerciasis (using individual recombinant clones OV-10, OV-11 and OV-16, and the OV-7/OV-10/OV-16 tri-cocktail, in an enzyme-linked immunosorbent assay) and for circulating antigen-based diagnosis of bancroftian filariasis (using the TropBio and the ICT card tests). Some immunological cross-reactivity was observed with all tests. When using individual recombinant O.volvulus antigens, the highest assay indices were obtained for clone OV-10, and the lowest for clone OV-16. Testing the serum responses against the tri-cocktail of recombinant antigens did not notably improve the assay indices. Two of 40 serum samples from individuals with patent dracunculiasis gave a false positive response in the ICT test and one of these was also positive in the TropBio test. Possible implications of applying these diagnostic assays in areas endemic for dracunculiasis are discussed.
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PMID:The significance of guinea worm infection in the immunological diagnosis of onchocerciasis and bancroftian filariasis. 986 67

We report here the evaluation of the potential of a serologic test to determine the endemicity of onchocercal infection in hyper, meso, and hypoendemic communities by the detection of antibodies to a cocktail of recombinant antigens. Parasitologic parameters of infection prevalence and intensity were compared with serologic results. Infection prevalence by serology was consistently but not significantly higher than that defined by parasitology. Differences between the communities defined by microfilarial load (CMFL) and a measurement of Onchocerca volvulus-specific antibody levels (serologic index [SI]) were similar. When stratified by age, differences were more significant in the younger age groups. If a sentinel population of 5-15-year-old individuals was used to compare communities, all could be equally ranked by serologic and parasitologic parameters. The SI of the sentinel population gave a better distinction between each community than the SI of the whole and would be sufficiently sensitive to measure the changes in endemicity that would be required for onchocerciasis control programs.
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PMID:A cocktail of recombinant Onchocerca volvulus antigens for serologic diagnosis with the potential to predict the endemicity of onchocerciasis infection. 988 93

Infection with the parasitic nematode Onchocerca volvulus can lead to severe visual impairment and blindness. In an effort to characterize the molecular basis for the inflammatory response in the cornea, we have developed a murine model for O. volvulus-mediated keratitis in which parasite antigens are injected into the corneal stroma of sensitized mice. This model reproduces the two main clinical features of human disease, corneal opacification and neovascularization. Histological analysis of corneas from these mice reveals a biphasic recruitment of neutrophils and eosinophils to the central cornea, along with a small, but persistent number of CD3+ cells. In this review, we present evidence that production of antigen-specific T cell and antibody responses are essential for development of O. volvulus keratitis, and we propose a sequence of molecular and cellular events that lead to migration of inflammatory cells to the cornea and to loss of corneal clarity.
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PMID:Immune mechanisms in Onchocerca volvulus-mediated corneal disease (river blindness). 1112 54

Onchocerciasis is a debilitating parasitic infection caused by the filarial nematode Onchocerca volvulus. Infections are chronic, and persistence of the parasites for several years argues for highly adapted mechanisms of immune evasion. Due to the restricted host repertoire of O. volvulus, we have used the cattle parasite Onchocerca ochengi to investigate the nature of immunomodulation underpinning these long-term infections. Cattle were infected with a single inoculation of 350 infective-stage larvae under laboratory conditions (n = 6). Intradermal nodules containing immature adult worms were detected from 110 days postinfection, and microfilariae in skin were detected from day 280 postinfection. Parasite-specific responses during early infection were nonpolarized with respect to the major Th cytokines (interleukin-4 [IL-4], IL-2, and gamma interferon [IFN-gamma]) produced by antigen-stimulated peripheral blood mononuclear cells (PBMC) or serum antibody isotypes. Antigen-induced proliferation of PBMC peaked shortly after exposure and remained high during the prepatent infection. As the parasites matured and animals developed patent infections, there was a profound down-regulation of lymphoproliferation, accompanied by sharp falls in the expression of both IL-4 and IFN-gamma and a gradual decline in IL-2. Levels of immunoglobulin G2 (IgG2) fell, while those of IgG1 remained high. We conclude that neither a classical Th2 response nor a simple Th1-to-Th2 switch is sufficient to explain the immunomodulation associated with patent Onchocerca infections. Instead, there is an initial Th0 response, which matures into a response with some, but not all of the features of a Th2 response. The natural host-parasite relationship of O. ochengi in cattle may be useful as both a descriptive and predictive tool to test more refined models of immunomodulation in onchocerciasis.
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PMID:Down-regulated lymphoproliferation coincides with parasite maturation and with the collapse of both gamma interferon and interleukin-4 responses in a bovine model of onchocerciasis. 1140 68

Four adult dogs that had spent their entire life in Hungary, were found to be infected with filaroid nematodes of the genus Onchocerca. The morphology and location of the parasites as well as pathological lesions were similar to those described earlier in the one Hungarian and five US dogs. Only moderate morphological differences were noted between the adults of Onchocerca sp. infecting dogs and O. volvulus of man or O. lienalis of cattle. Nevertheless, the morphology of microfilariae of Onchocerca from dogs is unique within the genus. Their length was less than half the length of microfilariae of other Onchocerca spp. known so far. In addition to size differences, several characteristic morphological features were observed. The unsuccessful attempt to infect dogs with O. lienalis, the absence of O. volvulus and O. lienalis in endemic regions of canine onchocercosis, the different size, morphology, and location of the adults in dogs and cattle, the exceptionally small size and unique morphology of microfilariae of Onchocerca of canids indicate that a distinct species might be responsible for canine onchocercosis. Since the larval concentration in the skin was high (50-3600 microfilariae g(-1)) in all affected dogs, the diagnosis prior to surgical removal of worm nodules can be based on the examination of a small skin snip collected from the head or abdominal region. Infections in dogs may provide a model to study human onchocercosis, therefore, further studies are encouraged on the feasibility of experimental infection of dogs with this Onchocerca species.
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PMID:Ocular onchocercosis in dogs: aberrant infection in an accidental host or lupi onchocercosis? 1158 40

Infection by onchocerca volvulus, a parasitic worm, causes onchocerciasis (river blindness), a debilitating and often blinding disease endemic to tropical areas of Africa and Central and South America. The adult onchocerca volvulus invades the human host where it lives and reproduces for up to 14 years, creating millions of infant worms which cause itching, loss of skin color, rapid aging, and disfiguring skin disease in the host. Onchocerciasis often causes blindness in the human host by approximately age 35 years, and is the third leading cause of blindness in Africa. Onchocerca volvulus is transmitted among humans through the bite of blackflies which breed in fast-flowing rivers. The Onchocerciasis Control Program (OCP) was formally launched in 1974 by the UN's Food and Agriculture Organization (FAO), the UN Development Program (UNDP), the World Bank, and the World Health Organization (WHO) in Benin, Burkina Faso, Ghana, Cote d'Ivoire, Mali, Niger, and Togo. Vector control is the central strategy of the OCP, consisting of weekly helicopter spraying of larvacide to prevent the blackfly from reproducing and transmitting the disease. In addition, Merck & Co. is providing drug therapy against the infant worms in the human host free of charge to 16 million people in endemic areas. Onchocerciasis has now almost been eradicated in the 7 original target countries. Also through the OCP, by 1996, more than 34 million people were protected against the disease, about 2 million who were seriously infected have fully recovered, and an estimated 600,000 people have been prevented from going blind. 12 million infants born since the launch of the OCP face no risk of contracting the disease, and approximately 25 million hectares of arable fertile riverine land has been opened for resettlement. Labor productivity has also increased.
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PMID:River blindness. Protection for 54 cents a year. 1234 35

Infections with Wuchereria bancrofti causing lymphatic filariasis still represent one of the major health problems in the tropics, with 120 million people infected and over 750 million exposed to this filarial parasite. We have studied lymphatic filariasis infections as part of a multi-parasite survey in a village community in the savannah of northern Nigeria. We analysed serum samples from 341 individuals aged 5-70 years, detecting a W. bancrofti circulating antigen using the commercially available ICT Filariasis card test. The prevalence of infections was 10% and clearly age-dependent, increasing from below 2% in children to over 20% in subjects older than 40 years. Measuring IgG4 antibodies against the recombinant W. bancrofti antigen SXP1 showed that 36% of all tested individuals had been at least exposed to the parasite. Antibody levels also increased very significantly with age. A further analysis measuring Onchocerca volvulus-specific IgG4 antibodies showed a very significant association between infections with O. volvulus and those with W. bancrofti. Our data show that infections with W. bancrofti in Nigeria are still a frequently occurring health problem, since they are more prevalent than previously reported, and that individuals with an O. volvulus infection are more often infected with W. bancrofti than expected statistically.
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PMID:Analysis of Wuchereria bancrofti infections in a village community in northern Nigeria: increased prevalence in individuals infected with Onchocerca volvulus. 1254 43


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