SEARCH · PubMed Health

Results for “Onchocerca volvulus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources

PubMed1996

Absence of cellular responses to a putative autoantigen in onchocercal chorioretinopathy. Cellular autoimmunity in onchocercal chorioretinopathy.

PURPOSE: Onchocerciasis is a major cause of blindness in the developing world. An autoimmune pathogenesis for onchocercal chorioretinopathy was proposed after the identification of a recombinant Onchocerca volvulus antigen (designated Ov39) demonstrated immunologic crossreactivity with a component of the retinal pigment epithelium and other ocular tissues. The aim of this study was to determine whether patients with onchocercal chorioretinopathy have enhanced lymphoproliferative responses to Ov39 compared to those without chorioretinal disease. METHODS: Lymphocyte blastogenic assays were performed using peripheral blood mononuclear cells (PBMCs) from patients with and without evidence of chorioretinopathy. PBMCs were cultured with Ov39, and supernatant fluids from Ov39-stimulated PBMCs were used to determine levels of the cytokines, interferon-gamma, and interleukin-5. RESULTS: Lymphoproliferative responses to Ov39 were not enhanced in patients with onchocercal chorioretinopathy compared to those without clinical evidence of chorioretinal disease. CONCLUSIONS: A role for Ov39-specific cellular autoreactivity in the pathogenesis of onchocercal chorioretinopathy could not be demonstrated.

Adolescent↗

PubMed1999

Eosinophil sequestration and activation are associated with the onset and severity of systemic adverse reactions following the treatment of onchocerciasis with ivermectin.

To investigate the role of eosinophil activation and sequestration in the development and severity of adverse reactions after the treatment of Onchocerca volvulus infection, 40 O. volvulus-infected Ghanaians were randomized to receive placebo or standard- or high-dose ivermectin. Subjects were examined for typical physiologic and clinical events before and up to 48 h after treatment. Plasma samples were tested for interleukin (IL)-5 and eosinophil degranulation products (e.g., eosinophil-derived neurotoxin, EDN). After treatment, peripheral eosinophil counts declined in ivermectin-treated groups (P<.001), whereas circulating levels of IL-5 (P<.01) and EDN (P<.05) increased. Cumulative levels of IL-5 and EDN correlated with reaction scores (P<.01). High-dose ivermectin was associated with more-severe reactions, more-profound eosinopenia, and higher circulating levels of IL-5 and EDN, compared with the standard dose. These results suggest that eosinophil sequestration and activation/degranulation are associated with the initiation and severity of ivermectin-associated adverse reactions.

Agranulocytosis↗

PubMed2000

A rapid-format antibody card test for diagnosis of onchocerciasis.

Improved methods are needed for field diagnosis of onchocerciasis, to support efforts aimed at elimination of the disease. A rapid-format card test was evaluated that detects IgG4 antibodies to recombinant Onchocerca volvulus antigen Ov16 with serum samples from patients with onchocerciasis and with various types of control serum samples. The sensitivity of the test with serum samples from 106 microfilariae-positive subjects was 90.6%. The test was equally sensitive with serum samples obtained from patients in Africa and Latin America. Specificity was excellent; positive tests were observed for 2 of 38 serum samples from patients with other filarial infections and for 1 of 23 serum samples from patients with nonfilarial helminth infections. The 3 "false-positive" serum samples were from West Africans who could have been coinfected with onchocerciasis. No positive tests were observed with nonendemic serum samples from normal adults, patients with autoimmune disorders, or patients with the hyper-IgE syndrome. This new test holds great promise as a simple tool for diagnosis of onchocerciasis.

Adult↗

PubMed1994

Immunity to onchocerciasis: identification of a putatively immune population in a hyperendemic area of Ecuador.

The existence of immunity to Onchocerca volvulus (Ov) infection is suggested by the presence of uninfected persons in hyperendemic areas. A major barrier to the study of immunity has been the correct identification of putatively immune (PI) subjects. To identify a PI group in a hyperendemic area in Ecuador, clinical and epidemiologic information was combined with a polymerase chain reaction (PCR)-based assay identifying Ov DNA in skin snips and a recombinant antigen-based ELISA. Comparison of immune responses revealed that PI subjects had significantly lower levels of Ov-specific IgG, IgG subclasses, and IgE than infected (INF) subjects. Female subjects were significantly more likely to be PI than male subjects, and INF female subjects had significantly lower levels of Ov-specific IgG, IgG1, and IgG3 than INF male subjects. Thus, the use of molecular-based techniques has helped to define more precisely the PI state in onchocerciasis.

Adolescent↗

PubMedDate not supplied

Adverse reactions after community treatment of onchocerciasis with ivermectin in Guatemala.

Male and female residents on a Guatemalan coffee plantation where Onchocerca volvulus infections were hyperendemic were offered oral ivermectin (100-200 micrograms/kg) as part of a community-wide treatment programme for onchocerciasis. Forty-five persons were treated and then questioned daily for 28 d about changes in their health. Those with complaints were monitored until all signs and symptoms had resolved. Sixty-seven percent complained of some adverse event after treatment; 60% developed observable adverse reactions attributed clinically to ivermectin. No reaction was life-threatening; the most common were oedema (53%) and fever (47%). Expulsion of intestinal helminths was reported by 38%. Almost all reactions began 24-48 h after treatment; their mean duration was 5 d, despite treatment with acetaminophen and antihistamines. Three patients had oedematous changes lasting over 2 weeks. Incidence, but not severity, of reactions was related to the pretreatment density of microfilariae in skin.

Adolescent↗

PubMed1998

Filarial nematode parasites secrete a homologue of the human cytokine macrophage migration inhibitory factor.

Filarial nematode parasites establish long-term chronic infections in the context of an antiparasite immunity that is strongly biased toward a Th2 response. The mechanisms that lead to this Th2 bias toward filarial antigens are not clear, but one possibility is that the parasites produce molecules that have the capacity to proactively modify their immunological environment. Here we report that filarial parasites of humans secrete a homologue of the human proinflammatory cytokine macrophage migration inhibitory factor (MIF) that has the capability of modifying the activity of human monocytes/macrophages. A cDNA clone isolated from a Brugia malayi infective-stage larva expression library encoded a 12.5-kDa protein product (Bm-MIF) with 42% identity to human and murine MIF. MIF homologues were also found to be expressed in the related filarial species Wuchereria bancrofti and Onchocerca volvulus. Bm-mif was transcribed by adult and larval parasites, and the protein product was found in somatic extracts and in the parasite's excretory-secretory products. Immunohistocytochemistry revealed that Bm-MIF was localized to cells of the hypodermis/lateral chord, the uterine wall, and larvae developing in utero. Unexpectedly, the activities of recombinant Bm-MIF and human MIF on human monocytes/macrophages were found to be similar. When placed with monocytes/macrophages in a cell migration assay, Bm-MIF inhibited random migration. When placed away from cells, Bm-MIF induced an increase in monocyte/macrophage migration that was specifically inhibited by neutralizing anti-Bm-MIF antibodies. Bm-MIF is the first demonstration that helminth parasites produce cytokine homologues that have the potential to modify host immune responses to promote parasite survival.

Amino Acid Sequence↗

PubMed2004

The relationships between the burden of adult parasites, host age and the microfilarial density in human onchocerciasis.

We investigate the relationship between the microfilarial density in the skin and the burden of adult female Onchocerca volvulus by analysing pre-control nodulectomy data which allow for a direct approach, independent of exposure. The data of 169 patients in Burkina Faso and 182 patients in Liberia represent savannah and forest onchocerciasis in West Africa, respectively. Whereas in Burkina Faso, a saturating relationship between microfilarial density and worm burden suggests the operation of density-dependent processes within human hosts, the Liberian data show a linear relationship implying no density dependence. The differences may derive from differences between both parasite strains, i.e. the savannah or the forest strain of O. volvulus. Consistently for both parasite strains and independent of the worm burden, the microfilarial density increases with host age emphasising the concept of the acquisition of immunological tolerance. In male hosts in Liberia, the microfilarial density increases stronger with the worm burden than in female hosts, whereas such sex-specific differences cannot be found in Burkina Faso. In the methodological part of this investigation, we suggest the beta-distribution to be most appropriate for describing variability in microfilarial densities and we present an approach to consider the uncertainty in the adult parasite burden which cannot be determined precisely in helminth infections. Implications of density dependence are discussed with respect to immunological processes in the human host and with respect to the success of control programs. The relationships described show that regulatory processes between the parasite and the human host are multi-dimensional, operating within a high degree of biological variability.

Age Factors↗

PubMed2005

Human infection patterns and heterogeneous exposure in river blindness.

Here we analyze patterns of human infection with Onchocerca volvulus (the cause of river blindness) in different continents and ecologies. In contrast with some geohelminths and schistosome parasites whose worm burdens typically exhibit a humped pattern with host age, patterns of O. volvulus infection vary markedly with locality. To test the hypothesis that such differences are partly due to heterogeneity in exposure to vector bites, we develop an age- and sex-structured model for intensity of infection, with parasite regulation within humans and vectors. The model is fitted to microfilarial data from savannah villages of northern Cameroon, coffee fincas of central Guatemala, and forest-dwelling communities of southern Venezuela that were recorded before introducing ivermectin treatment. Estimates of transmission and infection loads are compared with entomological and epidemiological field data. Host age- and sex-heterogeneous exposure largely explains locale-specific infection patterns in onchocerciasis (whereas acquired protective immunity has been invoked for other helminth infections). The basic reproductive number, R0, ranges from 5 to 8, which is slightly above estimates for other helminth parasites but well below previously presented values.

Age Factors↗

PubMed1995

Onchocerciasis and human immunodeficiency virus in western Uganda: prevalences and treatment with ivermectin.

Epidemiologic investigations were made to assess the interaction between onchocerciasis and human immunodeficiency (HIV) type 1 infection and the efficacy of ivermectin treatment. Among 1,910 Onchocerca volvulus carriers in a hyperendemic focus, 73 (3.8%) were concurrently infected with HIV and 20 (7.2%) of 276 persons without microfilariae (mf) were HIV-seropositive. A stratified analysis showed no epidemiologic association between onchocerciasis and HIV infection. Consistently, a microfilaria density of 11.9 mf/mg of skin in HIV-positive subjects and 17.7 mf/mg in HIV-negatives ones was observed. During mass treatment of onchocerciasis with a single dose of 150 micrograms/kg of ivermectin, no difference of the efficacy was detected between persons with or without HIV and side effects in the two groups were similar. Even in HIV-positive persons with a reduced ratio of CD4+:CD8+ cells and reduced numbers of CD4+ cells, a significant reduction of their microfilaria density was observed after treatment with ivermectin. Thus, in HIV-endemic areas, the usual dose of ivermectin can be administered during mass treatment.

Adolescent↗

PubMed2005

Development and evaluation of an antigen detection dipstick assay for the diagnosis of human onchocerciasis.

To improve on the diagnosis of onchocerciasis, especially light infections, we developed and evaluated an oncho-dipstick test based on the detection of Onchocerca volvulus specific antigens in urine and tears. The test was able to detect as little as 25 ng/ml of parasite specific antigens in samples and took as little as 3 h. Evaluation of the assay on 456 residents of an onchocerciasis hyperendermic area in Cameroon resulted in 408 (89.5%) positives in urine and 374 (82%) positives in tears. The prevalence of onchocerciasis in the study area, as determined by Rapid Epidemiological Mapping of Onchocerciasis (REMO) and skin snip methods, was 52 and 36.8%, respectively. The sensitivity of the oncho-dipstick assay was 100% in urine and 92% in tears; its specificity was 100% in both. Concordance between urine and tear test results from the same individuals was 87%. The test strips were sufficiently reactive when left at room temperature for up to 8 months. The test would be useful for laboratory diagnosis of onchocerciasis in low transmission zones and to ascertain successful treatment of patients in experimental drug studies.

Animals↗

PubMed2005

Density dependence and overdispersion in the transmission of helminth parasites.

The influence of density-dependent processes on the transmission of parasitic helminths is determined by both the severity of the regulatory constraints and the degree of parasite overdispersion among the host population. We investigate how overdispersed parasite distributions among humans influence transmission levels in both directly- and indirectly-transmitted nematodes (Ascaris lumbricoides and Onchocerca volvulus). While past work has assumed, for simplicity, that density dependence acts on the average worm load, here we model density-dependence as acting on individual parasite burdens before averaging across hosts. A composite parameter, which we call the effective transmission contribution, is devised to measure the number of transmission stages contributed by a given worm burden after incorporating over-dispersion in adult worm mating probabilities and other density-dependent mechanisms. Results indicate that the more overdispersed the parasite population, the greater the effect of density dependence upon its transmission dynamics. Strong regulation and parasite overdispersion make the relationship between mean worm burden and its effective contribution to transmission highly non-linear. Consequently, lowering the intensity of infection in a host population using chemotherapy may produce only a small decline in transmission (relative to its initial endemic level). Our analysis indicates that when parasite burden is low, intermediate levels of parasite clustering maximize transmission. Implications are discussed in relation to existing control programmes and the spread of anthelmintic resistance.

Animals↗

PubMed1993

Description of a computer model of forest onchocerciasis transmission and its application to field scenarios of vector control and chemotherapy.

This paper describes a computer simulation model for onchocerciasis (SIMON). Using epidemiological and entomological data from a specific hyperendemic village in the forest area of Sierra Leone, the model is used to examine the effect of vector and chemotherapeutic control strategies, both separately and in combination, as well as the risk to an uninfected population caused by immigrant, infected Simulium damnosum and humans. The model suggests that, in this village, the human population of about 420 requires an average annual input of about 200 mature fecund, female Onchocerca volvulus per year to maintain a skin-snip prevalence of just under 70%. SIMON also predicts that 99% effective vector control would lead to eradication of all adult worms in 18 years, and that abandoning control before 14 years could lead to recrudescence. Chemotherapy with ivermectin at six-month intervals reaching 90% of eligible persons (effective 66%) might take 29 years to achieve eradication because of continuing transmission, particularly in the early years, but it would probably be possible to abandon treatments after 18 years because the residual worm population would no longer be self-sustaining. Combined ivermectin and vector control, both at reduced levels, could be as effective as 99% vector control. Immigrant infected flies are likely to pose a greater threat to an uninfected human population than small numbers of infected persons. The model suggests that, at levels of infection undetectable by skin-snip, the parasite could linger in the human population for 30 or more years sustained by sporadic transmission.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed2001

Long-term assessment of insecticides treatments in West Africa: aquatic entomofauna.

For the control of the Onchocerca volvulus vector in West Africa, up to 18,000 km of rivers from 1975 and up to 50,000 km from 1989 had been partly sprayed weekly with insecticides as part of the Onchocerciasis Control Programme (OCP). To evaluate the possible short-term and long-term effects of the application of insecticides on the non-target fauna, an aquatic monitoring programme was set up during the initial phase of the programme. By analysing the invertebrate data, which were collected using various sampling strategies from four different countries between 1977 and 1996, this paper evaluates the long-term changes of the invertebrate populations with respect to their taxonomic composition as well as their trophic structures. The discussed results of the applied numerical analysis strategy suggest that neither the taxonomic nor the trophic structures are greatly altered from the range of biological, flow-related variation that normally occurs in the studied river systems. This allows us to conclude that the biological variation found here is ecologically acceptable.

Africa, Western↗

PubMed2001

Distinct roles for PECAM-1, ICAM-1, and VCAM-1 in recruitment of neutrophils and eosinophils to the cornea in ocular onchocerciasis (river blindness).

Infiltration of granulocytes into the transparent mammalian cornea can result in loss of corneal clarity and severe visual impairment. Since the cornea is an avascular tissue, recruitment of granulocytes such as neutrophils and eosinophils into the corneal stroma is initiated from peripheral (limbal) vessels. To determine the role of vascular adhesion molecules in this process, expression of platelet endothelial cell adhesion molecule 1 (PECAM-1), ICAM-1, and VCAM-1 on limbal vessels was determined in a murine model of ocular onchocerciasis in which Ags from the parasitic worm Onchocerca volvulus are injected into the corneal stroma. Expression of each of these molecules was elevated after injection of parasite Ags; however, PECAM-1 and ICAM-1 expression remained elevated from 12 h after injection until 7 days, whereas VCAM-1 expression was more transient, with peak expression at 72 h. Subconjunctival injection of Ab to PECAM-1 significantly inhibited neutrophil recruitment to the cornea compared with eyes injected with control Ab (p = 0.012). Consistent with this finding, corneal opacification was significantly diminished (p < 0.0001). There was no significant reduction in eosinophils. Conversely, subconjunctival injection of Ab to ICAM-1 did not impair neutrophil recruitment, but significantly inhibited eosinophil recruitment (p = 0.0032). Injection of Ab to VCAM-1 did not significantly inhibit infiltration of either cell type to the cornea. Taken together, these results demonstrate important regulatory roles for PECAM-1 and ICAM-1 in recruitment of neutrophils and eosinophils, respectively, to the cornea, and may indicate a selective approach to immune intervention.

Animals↗

PubMedDate not supplied

The significance of guinea worm infection in the immunological diagnosis of onchocerciasis and bancroftian filariasis.

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.

Adolescent↗

PubMed1998

The role of eosinophils and neutrophils in helminth-induced keratitis.

PURPOSE: Intrastromal injection of mice with antigens from the parasitic helminth that causes river blindness (Onchocerca volvulus) induces eosinophil recruitment to the corneal stroma at the time of maximum corneal opacification and neovascularization. The present study was conducted to examine the role of eosinophils and neutrophils in onchocercal keratitis in control C57Bl/6 mice and in interleukin-5 gene knockout (IL-5(-/-)) mice. METHODS: C57Bl/6 and IL-5(-/-) mice were immunized subcutaneously and injected intrastromally with soluble O. volvulus antigens. Mice were killed at various times thereafter. Development of keratitis was assessed by slit lamp examination, and inflammatory cells in the cornea were identified by immunohistochemistry. RESULTS: A biphasic recruitment of inflammatory cells was observed in C57Bl/6 mice; neutrophils predominated during the first 72 hours after intrastromal injection and subsequently declined, whereas eosinophil recruitment increased as time elapsed and comprised the majority (90%) of cells in the cornea by day 7. In contrast, neutrophils were the predominant inflammatory cells in IL-5(-/-) mice at early and late time points and were associated with extensive stromal damage and corneal opacification and neovascularization. Eosinophils were not detected in these mice at any time. CONCLUSIONS: In the absence of eosinophils, neutrophils can mediate keratitis induced by helminth antigens. Together with the early neutrophilic infiltrate in control animals, these observations indicate that neutrophils have an important role in onchocercal keratitis.

Animals↗

PubMed1996

Cloning and expression of DiT33 from Dirofilaria immitis: a specific and early marker of heartworm infection.

Dirofilaria immitis is an important filarial parasite of dogs and cats, and a useful model for human filariasis. Current diagnostic tests for heartworm infection in animals rely on the presence of fecund female worms (usually found 6.5 months post-infection or later) and therefore fail to detect pre-patent infections. Putative pepsin inhibitors from 2 filarial parasites of humans namely Onchocerca volvulus (Ov33, Oc3.6, OvD5B) and Brugia malayi (Bm33), have been shown to be useful in diagnosis of onchocerciasis and lymphatic filariasis, respectively. Previous studies have suggested that a homologue exists in D. immitis (DiT33), which may have potential in diagnosis of heartworm infection. In this study, the isolation and characterization of a cDNA clone encoding DiT33 is described. This cDNA contains 12 bases of the nematode-specific 22 nucleotide spliced leader sequence and encodes a 26.4 kDa-protein with a high level of similarity (87-89%) to other filarial members of the family. DiT33 was over-expressed in E. coli as a fusion with the maltose-binding protein and serological analysis was performed using a panel of clinically defined dog sera. The findings of this study indicate that DiT33 is a promising antigen for the early detection of D. immitis and may be a valuable tool in the control and management of heartworm infection.

Amino Acid Sequence↗

PubMed2006

Consequences of vector behavior in epidemiology of onchocerciasis on the Firestone Rubber Plantation in Liberia.

In the current study, we have assessed the distribution of black fly vectors and the occurrence of onchocerciasis among residents of the Firestone Rubber Plantation (FRP) in Liberia. The degree of endemicity of onchocerciasis on the FRP is correlated with the breeding of Simulium yahense on the Du River and Simulium soubrense on the Farmington River, as well as with the feeding behavior of these black fly vectors. S. yahense is highly anthropophilic and highly susceptible to Onchocerca volvulus, thus, it is apparently the primary vector of O. volvulus on the plantation. S. soubrense is predominantly zoophilic; consequently, it has a low capacity for transmitting of O. volvulus to humans. The prevalence of the disease is hyperendemic in the divisional camps near the Du River, affecting 77.6% to 94.4% of males and 64.9% to 88.9% of females. In the camps along the Farmington River, the disease is hypoendemic, affecting 26.1% to 49.2% of males and 25.6% to 35.1% of females. The mean intensity of infection in the camps near the Du River was 14.1 microfilariae (mf)/mg of skin in males and 13.7 mf/mg of skin in females. The density of microfilariae in people in the camps along the Farmington River was 4.8 mf/mg of skin in males and 1.9 mf/mg of skin in females. The age-specific infection in camps along both rivers substantially increased after the ages 21-30, reaching a maximum at ages 41-50. The mean density of mf/mg of skin in three anatomic locations (calf, hip, and shoulder) was 28.0, 24.5, and 14.1 mf/mg of skin, respectively, for those living on the Du River, and 10.2, 7.6, and 5.8 mf/mg of skin, respectively, for those on the Farmington River.

Adolescent↗