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

Onchocerciasis ('River Blindness'), caused by the filarial nematode Onchocerca volvulus is of major public health importance in West Africa. Ivermectin, a drug originally developed for veterinary use, is now being incorporated in control strategies but whilst it has potent efficacy against L1 larvae (microfilariae), ivermectin is not lethal to adult (L5) O. volvulus, nor to adults of the related cattle parasite O. ochengi. We have exploited this model to determine if ivermectin has prophylactic activity against naturally transmitted, O. ochengi infections in a controlled, prospective study in northern Cameroon. Calves were treated monthly with ivermectin at either 200 micrograms/kg or 500 micrograms/kg for 21 months. None of 15 treated calves developed adult worm infection, whereas 5/6 untreated controls became infected (P < 0.001) with a total of 54 O. ochengi nodules, and all 5 developed patent microfilaridermia. These results have significant implications for the use of ivermectin in humans, and suggest that strategic chemotherapy at times of maximal transmission will confer prophylactic as well as therapeutic benefits.
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PMID:Chemoprophylaxis of Onchocerca infections: in a controlled, prospective study ivermectin prevents calves becoming infected with O. ochengi. 1002 34

Epileptic seizures are frequent in neurocysticercosis and may occur during cerebral malaria. Findings are reported from a matched case-control study conducted in March 1996 in the savannah woodland region of northwest Central African Republic to determine whether any relation exists between Onchocerca volvulus infestation and epilepsy. About 70% of the study region's inhabitants are infested with O. volvulus. Each epileptic case was matched against 2 nonepileptic controls on the criteria of sex, age, residence, treatment with ivermectin, date of last ivermectin dose, and the number of ivermectin doses. Onchocerciasis was defined as at least 1 microfilaria observed in iliac crest skin snip biopsy. 187 cases and 374 controls were included in the study. 39.6% of the epileptics and 35.8% of the controls had onchocerciasis. The mean dermal microfilarial load was 26 microfilariae per mg of skin in the epileptics and 24 microfilariae per mg of skin in the controls. The relation between O. volvulus infestation and epilepsy was statistically nonsignificant.
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PMID:Onchocerciasis and epilepsy: a matched case-control study in the Central African Republic. 1008 46

During a routine entomological survey conducted within the framework of the Program to Control Onchocerciasis in West Africa, a female simulium forest fly was found to be contaminated by 13 Onchocerca volvulus larvae and 7 Onchocerca ochengi larvae. The two Onchocerca species were identified using specific DNA probes. We speculate that cross infection could be related either to behavioral factors, e.g. interruption of blood meals on two different hosts, or developmental factors, e.g. asynchronous development of parasites of the same species or specific differences in the duration of parasite cycles. Further study will be needed to determine the incidence and scope of cross infection in areas where accurate assessment of the impact of vector control on transmission of onchocerciasis in man is required.
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PMID:[A case of cross infection by Onchocerca volvulus and Onchocerca ochengi in Simulium damnosum S.L]. 1008 5

Two methods are being used to control onchocerciasis. The first has a delayed effect and consists in reducing or interrupting transmission of Onchocerca volvulus by eradication of the vector at its most vulnerable developmental stage, i.e. the larval stage. The second method has more immediate effects and consists in mass treatment using ivermectin, the only widely available drug, to reduce the density of microfilariae (the pathogenic stage of the parasite) in the population. Both strategies have been implemented within the framework of two international programs: the Onchocerciasis Control Program (OCP) in West Africa, which started in 1974 and will continue until the end of 2002, and the African Program for Onchocerciasis Control (APOC), which was launched in 1995 and will last for 12 years. This article presents an overview of the efficacy of available control tools, as well as the objectives, strategies, organization, and results of the two ongoing control programs. Also dealt with are future perspectives of onchocerciasis control including monitoring techniques to maintain OCP gains, and research to develop new control tools and optimize the program efficacy.
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PMID:[The campaign against onchocerciasis in Africa: update]. 1008 9

Eosinophils, eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN/EPX), myeloperoxidase (MPO) and IgE were measured in blood, serum and/or urine in Schistosoma haematobium- and Onchocerca volvulus-infected Guineans and O. volvulus- and S. haematobium-negative Guineans coinfected or infected with intestinal nematodes. The number of eosinophils and levels of eosinophil granule proteins but not of MPO were found to be strongly elevated in all Africans as compared to European controls. The highest serum ECP and serum and urinary EDN/EPX levels were observed in the hyperreactive form of onchocerciasis (sowda). Onchocerciasis patients and O. volvulus-negative Africans coinfected or infected with intestinal nematodes (hookworm and/or Ascaris lumbricoides) revealed higher serum granule protein concentrations and/or absolute eosinophil counts and urinary ECP than those without nematode infections. Statistical differences between both sections were found for the absolute eosinophil counts and for serum EDN/EPX and IgE in generalized onchocerciasis, and for urinary ECP in sowda, indicating stimulation of the eosinophil potential of O. volvulus-positive patients by coexistent hookworm infection. This worm species, in contrast to A. lumbricoides, causes especially high eosinophil counts and EDN/EPX and IgE levels. From these results it is concluded that in nematode diseases, ECP and EDN/EPX levels reflect the degree of antigenic stimulation, eosinophil activation and eosinophil turnover rates. Serum ECP and serum and urinary EDN/EPX may, therefore, serve as parameters to monitor helminth infection. Urinary ECP may be a marker of eosinophiluria secondary to urogenital manifestation of S. haematobium. It is elevated in hyperreactive onchocerciasis activated by intestinal nematodes.
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PMID:Eosinophils, eosinophil cationic protein and eosinophil-derived neurotoxin in serum and urine of patients with onchocerciasis coinfected with intestinal nematodes and in urinary schistosomiasis. 1020 16

Onchocerciasis remains an important public health problem throughout much of sub-Saharan Africa. Nigeria is the country whose population is most afflicted by onchocerciasis; however, little is known concerning the epidemiology of onchocerciasis in this country. Previous studies demonstrated that onchocerciasis in West Africa exists in two forms, which differ in their clinical and epidemiologic characteristics. This is believed to be due to the existence of 2 strains of Onchocerca volvulus, the causative agent of onchocerciasis. The O-150 polymerase chain reaction has been developed to differentiate these 2 strains, and this method has been used to map the distribution of the blinding and nonblinding strains of O. volvulus in Nigeria. The strain distribution is consistent with what is known concerning the ecology and epidemiology of onchocerciasis in this country. The results also suggest that migration may be affecting the historic distribution of the 2 strains of the parasite in Nigeria.
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PMID:Distribution of the blinding and nonblinding strains of Onchocerca volvulus in Nigeria. 1022 87

Human onchocerciasis (river blindness) is the filarial infection caused by Onchocerca volvulus and transmitted among people through the bites of the Simulium vector. Some 86 million people around the world are at risk of acquiring the nematode, with 18 million people infected and 600,000 visually impaired, half of them partially or totally blind. 99% of cases occur in tropical Africa; scattered foci exist in Latin America. Until recently control programmes, in operation since 1975, have consisted of antivectorial measures. With the introduction of ivermectin in 1988, safe and effective chemotherapy is now available. With the original Onchocerciasis Control Programme of West Africa coming to an end, both the new African Programme for Onchocerciasis Control and the Onchocerciasis Elimination Programme for the Americas, rely heavily on ivermectin self-sustained mass delivery. In consequence, the need for understanding the processes regulating parasite abundance in human and simuliid populations is of utmost importance. We present a simple mathematical framework built around recent analyses of exposure- and density-dependent processes operating, respectively, within the human and vector hosts. An expression for the basic reproductive ratio, R0, is derived and related to the minimum vector density required for parasite persistence in localities of West Africa in general and northern Cameroon in particular. Model outputs suggest that constraints acting against parasite establishment in both humans and vectors are necessary to reproduce field observations, but those in humans may not fully protect against reinfection. Analyses of host age-profiles of infection prevalence, intensity, and aggregation for increasing levels of endemicity and intensity of transmission in the Vina valley of northern Cameroon are in agreement with these results and discussed in light of novel work on onchocerciasis immunology.
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PMID:Population biology of human onchocerciasis. 1036 6

Onchocerciasis is a major cause of blindness. Although the World Health Organization has been successful in reducing onchocerciasis as a public health problem in parts of West Africa, there remain an estimated 17 million people infected with Onchocerca volvulus, the parasite that causes this disease. Ocular pathology can be manifested in any part of the eye, although disease manifestations are frequently characterized as either posterior or anterior eye disease. This review focuses on onchocerca-mediated keratitis that results from an inflammatory response in the anterior portion of the eye and summarizes what is currently known about human disease. This review also describes studies with experimental models that have been established to determine the immunological mechanisms underlying interstitial keratitis. The pathogenesis of keratitis is thought to be due to the host inflammatory response to degenerating parasites in the eye; therefore, the primary clinical symptoms of onchocercal keratitis (corneal opacification and neovascularization) are induced after injection of soluble O. volvulus antigens into the corneal stroma. Experimental approaches have demonstrated an essential role for sensitized T helper cells and shown that cytokines can regulate the severity of keratitis by controlling recruitment of inflammatory cells into the cornea. Chemokines are also important in inflammatory cell recruitment to the cornea, and their role in onchocerciasis is being examined. Further understanding of the molecular basis of the development of onchocercal keratitis may lead to novel approaches to immunologically based intervention.
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PMID:Pathogenesis of onchocercal keratitis (River blindness). 1039 75

Onchocerciasis, also known as "river blindness", presents a plenum of clinical manifestations which vary from one individual to another, and from one area to another. This large spectrum of clinical manifestations of the disease is an indication of the complexity of the pathogenesis of onchocerciasis and suggests that many interacting factors might influence the clinical features of the disease. The present study has focused on the heterogenicity of the host immune response as a plausible explanation for differences in clinical manifestations of the infection. Host genetic factors, namely HLA genes, might play an important role in determining the nature of the immune response mounted against the parasite Onchocerca volvulus, and thus the development of different manifestations of the infection. Genetic diversity of onchocerciasis was assessed in different endemic foci in Cameroon. In order to investigate the possibility that the Major Histocompatibility Complex (MHC) genes might be associated with the different clinical types of onchocerciasis, 146 subjects living in three endemic areas of Cameroon were studied. They were classified in four groups: A (asymptomatic subjects), P (putatively immune subjects) L (patients with localised disease) and G (patients with generalised disease). The four groups differed in the distribution of HLA class II alleles as determined by Direct Heteroduplex Analysis. On the one hand, allele HLA-DQA1*0501 appeared to be associated with protection against severe onchocerciasis; on the other, allele HLA-DQB1*0201 might play an important role in the severe form of the disease.
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PMID:[Variations under genetic control of onchocerca infection as a function of clinical profile in the endemic center of Cameroon]. 1039 95

This study investigated the effect of maternal Onchocerca volvulus infection on humoral and cellular responsiveness in newborn children and their mothers. Onchocerca volvulus-specific IgG isotypes and IgE were significantly elevated in infected mothers and their infants. One year post partum, O. volvulus-specific IgG4 was strongly reduced in children of infected mothers, while IgG1 responses weakened only slightly. Umbilical cord mononuclear blood cells (UCBC) and peripheral blood cells (PBMC) from mothers proliferated in response to phytohaemagglutinin (PHA), concanavalin A (Con A), and the bacterial antigens streptolysin-O (SL-O) or purified protein derivative (PPD). UCBC from neonates born to O. volvulus-infected mothers responded lower (P < 0.01) to Con A (at 5 micrograms/ml), PPD (at 10 and 50 micrograms/ml) and O. volvulus-derived antigens (OvAg) (at 35 micrograms/ml), and in parallel, a diminished cellular reactivity (P < 0.01) by PBMC was observed to OvAg in mothers positive for O. volvulus. Several Th1-type (IL-2, IL-12, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha)) and Th2-type (IL-4, IL-5, IL-10, IL-13) cytokines were secreted by UCBC and PBMC in response to OvAg, bacterial SL-O and PHA. OvAg did not stimulate IL-2 and none of the mitogens or antigens induced production of IL-4 in neonates. In response to OvAg, substantially elevated (P < 0.01) amounts of IFN-gamma were produced by UCBC from newborns of O. volvulus-infected mothers. UCBC secreted low levels of IL-5 and IL-13, while higher amounts of IL-10 were found (P < 0. 01) in newborns from onchocerciasis-free mothers. In conclusion, maternal O. volvulus-infection will sensitize in utero parasite-specific cellular immune responsiveness in neonates and activate OvAg-specific production of several Th1- and Th2-type cytokines.
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PMID:Prenatal immune priming in onchocerciasis-onchocerca volvulus-specific cellular responsiveness and cytokine production in newborns from infected mothers. 1040 26


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