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 991 records · Page 55Linked to original sources

PubMed1977

A comparison of individual dissection and mass separation for recovery of Onchocerca larvae from vector black flies.

The effectiveness of a mass separation technique, previously used for the extraction of larvae of lymphatic-dwelling filarial worms from batches of vector mosquitoes, was tested as a means of recovering infective-stage larvae of Onchocerca volvulus from Simulium ochraceum in Guatemala. Blood-engorged flies, collected from 10 infected human attractants, were maintained for 9 days to allow ingested microfilariae to develop to the infective stage. The numbers of Onchocerca larvae recovered after groups of these flies were crushed and washed into tissue culture fluid in Baermann funnels was compared with the numbers obtained by individual dissections of flies fed on the same subjects. The mass separation procedure gave a mean recovery rate of 0.03 larva/fly and detected larvae only in flies which had fed on those subjects with the highest microfilarial skin densities. Dissections yielded 0.50 larva/fly (a 16.7-fold increase) and detected larvae in flies collected from all test subjects. The explanation for the ineffectiveness of the mass separation technique may lie in the observed sluggishness of infective-stage Onchocerca larvae and a consequent inability to free themselves from the fly fragments in the Baermann funnel.

Animals↗

PubMed2006

Phylogenetic relationships of the Wolbachia of nematodes and arthropods.

Wolbachia are well known as bacterial symbionts of arthropods, where they are reproductive parasites, but have also been described from nematode hosts, where the symbiotic interaction has features of mutualism. The majority of arthropod Wolbachia belong to clades A and B, while nematode Wolbachia mostly belong to clades C and D, but these relationships have been based on analysis of a small number of genes. To investigate the evolution and relationships of Wolbachia symbionts we have sequenced over 70 kb of the genome of wOvo, a Wolbachia from the human-parasitic nematode Onchocerca volvulus, and compared the genes identified to orthologues in other sequenced Wolbachia genomes. In comparisons of conserved local synteny, we find that wBm, from the nematode Brugia malayi, and wMel, from Drosophila melanogaster, are more similar to each other than either is to wOvo. Phylogenetic analysis of the protein-coding and ribosomal RNA genes on the sequenced fragments supports reciprocal monophyly of nematode and arthropod Wolbachia. The nematode Wolbachia did not arise from within the A clade of arthropod Wolbachia, and the root of the Wolbachia clade lies between the nematode and arthropod symbionts. Using the wOvo sequence, we identified a lateral transfer event whereby segments of the Wolbachia genome were inserted into the Onchocerca nuclear genome. This event predated the separation of the human parasite O. volvulus from its cattle-parasitic sister species, O. ochengi. The long association between filarial nematodes and Wolbachia symbionts may permit more frequent genetic exchange between their genomes.

Animals↗

PubMed1991

Molecular cloning and characterization of recombinant parasite antigens for immunodiagnosis of onchocerciasis.

Immunological cross-reactivity among nematodes has hampered the development of specific serodiagnostic assays for onchocerciasis. In the present study, an Onchocerca volvulus adult worm complementary DNA expression library was differentially screened with human sera from patients infected with O. volvulus and with an omnibus anti-nematode serum pool comprised of sera from patients infected with Brugia malayi, Loa loa, Wuchereria bancrofti, Mansonella perstans, Strongyloides stercoralis, Ancylostoma duodenale, Ascaris lumbricoides, and Dracunculus medinensis. Seven Onchocerca-specific clones were identified and screened with individual onchocerciasis patient sera. Additional studies were performed to characterize the most immunoreactive clones, OC 3.6 and OC 9.3. OC 3.6 produced a 152-kD beta-galactosidase fusion protein that was recognized in dot-immunoblots by 54 of 55 sera from onchocerciasis patients (98%). The OC 3.6 DNA insert is 996 bp long with an open reading frame of 627 bp and a 369-bp untranslated 3' end. OC 3.6 is closely related to a previously reported clone (OV 33-3), but it differs from that clone at both the 5' and 3' ends. OC 9.3 contained a novel 565-bp insert and produced a 138-kD fusion protein that was recognized by 46 of 55 sera from onchocerciasis patients (83%). Additional studies are in progress to develop and evaluate immunodiagnostic tests for onchocerciasis based on measurement of antibodies to these promising recombinant antigens.

Amino Acid Sequence↗

PubMed1981

IgE antibodies in human onchocerciasis. Application of a newly developed radioallergosorbent test (RAST).

A radioallergosorbent test (RAST) was developed to detect IgE antibodies against adult Onchocerca volvulus antigens coupled to CnBr-activated Sepharose. Twenty-four out of 25 (96%) onchocerciasis sera were reactive. The lower limit of sensitivity was estimated to be at approx. 3 ng/ml IgE antibodies. Tests of sera from patients with non-filarial helminth infections showed much less cross-reactivity with RAST than with an enzyme-linked immunosorbent assay (ELISA) detecting IgG and IgM antibodies against the same antigen preparation. At a specificity comparable to that of RAST, the sensitivity of ELISA was only 61%. A heterologous antigen, prepared from female Dipetalonema viteae worms, was comparatively evaluated with O. volvulus. In RAST and ELISA, onchocerciasis sera were less reactive than against the O. volvulus antigen. Since sera from patients with non-filarial helminth infections were more reactive in RAST and almost equally reactive in ELISA using the D. viteae antigen, sensitivity was 83% for RAST and only 22% for ELISA (compared at the specificity identical to that of the O. volvulus RAST).

Animals↗

PubMed1979

Immunologic response in onchocerciasis: relations to microfilaria density in the skin biopsy and to some frequent symptoms.

During physical and immunologic investigations on onchocerciasis in 1,298 persons in the Republic of Liberia, the following results were obtained. There is a significant correlation between immune response and Onchocerca volvulus infection detected by a microfilaria-positive skin biopsy. On the other hand, the immune response is not influenced by the number of parasites in the skin, and there is no correlation of the immune response with Onchocerca nodules and with pruritus. There is a high proportion of serologically false-positive and false-negative results, and thus a diagnosis cannot be made simply by establishing evidence for antibodies in one person.

Adolescent↗

PubMed1979

Onchocerciasis focus in Colombia: follow-up study after 12 years.

This study is a follow-up of a 1965 investigation of the only known focus of Onchocerca volvulus in Colombia. In the first phase of the current study, 254 persons were examined. Of the 19 individuals found to be infected with O. volvulus, the youngest was a 16-year-old male. Among those included in the 1965 study, 22 were examined again for microfilariae. Two were positive in both studies, 4 were positive in 1965 but negative in 1977 and the remaining 16 were negative on both occasions. The prevalence of infection, based on identification of microfilariae in skin snips, was lower in the current study (7.5%) than the 15.1% recorded 12 years earlier. However, a 50% response to the Mazzotti test (administration of oral diethylcarbamazine) among a limited number of people upstream from the previously identified endemic area suggests that infection with O. volvulus may be quite widespread.

Adolescent↗

PubMed1987

Onchocerciasis in Ecuador: absence of microfilaraemia.

Blood samples from 497 people positive for onchocerciasis in the hyperendemic onchocercal focus in Ecuador were analysed for the presence of microfilaraemia using the Knott technique. No evidence of Onchocerca volvulus microfilaraemia was found, nor that of any other microfilaria.

Adult↗

PubMed1989

Ocular onchocerciasis and intensity of infection in the community. II. West African rainforest foci of the vector Simulium yahense.

A novel method of analysis was used to describe community patterns of ocular onchocerciasis in relation to the intensity of infection in West African forest villages where S. yahense is the sole vector. The pattern is completely different from that found in the savanna, even after correction for the intensity of infection as measured by the Community Microfilarial Load (CMFL). Lesions of the anterior segment of the eye as well as onchocercal blindness either do not occur or occur only sporadically with increasing CMFL in the Yahense forest whilst a steep linear relation exists between the prevalence of these lesions and the CMFL in the savanna. Lesions of the posterior segment of the eye are also less common in the Yahense forest. For a given skin microfilarial load, the ocular microfilarial load is lower in the Yahense forest. For a given ocular microfilarial load, a lower prevalence of eye lesions is found in the Yahense forest compared to the savanna. It is concluded that microfilariae of Onchocerca volvulus in the Yahense forest are less eye invasive than microfilariae from the savanna. Furthermore, they appear to be also less pathogenic to the eye. These findings explain why ocular onchocerciasis is relatively mild in the Yahense forest, in spite of the high intensities of O. volvulus infection in the community.

Animals↗

PubMed1989

Isolation of Onchocerca gibsoni tissue from frozen nodules for biochemical use.

A new procedure is described which enables gram quantities of adult Onchocerca tissue to be isolated from frozen connective tissue nodules, thus minimizing the risk of enzymatic degradation. Bovine connective tissue nodules containing adult Onchocerca gibsoni worms were obtained from Australia frozen at -70 degrees C and sectioned while still frozen into 3 mm thick slabs. The sections were thawed immediately before use, worm segments removed, rinsed, pelleted, and flash frozen in liquid nitrogen. Quality of the isolated material was demonstrated by the presence of an intact adult epicuticle as determined by electron microscopy, and by the presence of viable uterine larvae and cells. This procedure is applicable to other nodule-forming worms such as Onchocerca volvulus and is suitable for investigations which require the isolation of labile molecules or those present in minute quantities.

Animals↗

PubMed1997

Black fly (Diptera:Simuliidae) salivary secretions: importance in vector competence and disease.

When blood-feeding, black flies introduce secretions into the feeding lesion that act in a coordinated manner on the 3 arms of the vertebrate hemostatic system (platelet aggregation, coagulation, and vasoconstriction). Apyrase activity inhibits platelet aggregation and is ubiquitous in the saliva of black flies, although activity per gland varies by species and has a positive association with anthropophagy. Anticoagulants target components in the final common pathway of the coagulation cascade, including factors V, Xa, and II (thrombin). The antithrombin salivary protein may exert a redundant effect by inhibiting the role of thrombin in platelet aggregation. Antithrombin presence and activity also varies among black fly species, and exhibits a positive correlation with zoophagy. Vasodilation of capillaries to increase blood supply to the feeding wound appears to be an important requirement for Simulium spp., because substantial erythema-inducing activity, has been demonstrated in salivary glands of all New World species examined. Salivary glands of Simulium ochraceum (Walker), a highly anthropophilic vector of Onchocerca volvulus (Leuckhart), contain greater vasodilator activity than several other species, including S. metallicum Bellardi, a secondary zoophagic vector of human onchocerciasis. Simulium vittatum Zetterstedt saliva affects immune cell responses and cytokine production. The ability of the saliva to modulate components of the host immune system provides an opportunity for enhancing transmission of pathogens during bloodfeeding. Thus, the likely possibility that effective pathogen transmission relies on vector saliva may complement present efforts aimed at target epitopes of O. volvulus or identify additional molecules to be investigated as part of a "river blindness" vaccine cocktail. Components in saliva also may enhance the transmission of other microbial agents either by a cofeeding process similar to that observed in ixodid ticks or through rupture of the labrum during escape of Onchocerca infective stage larvae. In a few instances, saliva of some Simulium spp. also has been associated with extensive tissue and organ pathology, including hemorrhagic shock and death. Pathologic signs associated with this syndrome indicate an enhanced antihemostatic activity in saliva.

Animals↗

PubMed1987

The reduction in microfilariae loads in the skin and eye after nodulectomy in Ecuadorian onchocerciasis.

This study is concerned with the relationship between palpable onchocercal nodules and Onchocerca volvulus microfilarial loads in the skin. The number of microfilariae in clinically normal skin decreases as the distance from the nodule increases. Surgical removal of nodules reduces the microfilarial loads in 40 of 46 patients studied over a period of five months, with an average reduction of 65.4% of the prenodulectomy microfilarial load at the iliac crest. Complete elimination of detectable parasites was seen in some patients. Five individuals had increased microfilarial loads, all of which had developed new palpable nodules. Also, nodulectomy had a significant effect on ocular tissue, reducing the levels of parasites in the cornea and anterior chamber in 10 of 15 patients observed with no new nodules developing during the observation period. Both dermal and ocular clinical manifestations of onchocerciasis were reduced in a proportion of the patients. These parasitological and clinical findings provide evidence that nodulectomy is a beneficial procedure to O. volvulus infected patients in Ecuador by reducing both microfilarial loads and the degree of pathology.

Animals↗

PubMed1982

Clinical trials of amodiaquine in onchocerciasis.

Twenty onchocerciasis patients from the rain-forest zone of Western Nigeria were treated with amodiaquine in total dosages ranging from 22 to 68 mg/kg of body weight given over 2-9 days. There was no activity against either the microfilariae or adult forms of Onchocerca volvulus. It is concluded that the drug, which was poorly tolerated by 12 patients, is ineffective against human onchocerciasis.

Adult↗

PubMedDate not supplied

Immediate hypersensitivity responses in the immunopathogenesis of human onchocerciasis.

It is not clear what role immediate hypersensitivity immune responses have in the pathogenesis of human onchocerciasis, but it is certain that these responses are prominent both in the course of natural infection and during the Mazzotti reactions that follow treatment with diethylcarbamazine. In humans, the levels of total serum IgE associated with onchocerciasis are as high or higher than those associated with almost any helminth infection, although specific IgE antibodies to Onchocerca volvulus appear to be a small and still poorly characterized fraction of the total serum IgE. Evidence about the relationship of these prominent IgE responses in patients with onchocerciasis to the onchocercal skin disease that manifests as pruritus and papular eruptions is conflicting, but in a guinea pig model of ocular pathology induced by onchocerca microfilariae evidence for the pathogenetic importance of IgE and immediate hypersensitivity is much less equivocal. The suggestive findings from this model make it imperative to carry out similar studies of Onchocerca-affected human eyes to determine whether immediate hypersensitivity responses play a similar critical role in the pathogenesis of the ocular lesions in humans.

Animals↗

PubMed2004

Cattle protected from onchocerciasis by ivermectin are highly susceptible to infection after drug withdrawal.

Ivermectin administration is now the major tool in the control of human onchocerciasis (caused by Onchocerca volvulus) based on its suppression of microfilariae and hence the prevention of disease. However, in Africa, transmission is not eliminated and treated populations continue to be exposed to infective larval (L(3)) challenge, albeit at reduced levels. We have investigated whether protective immunity might develop under such conditions using the analogous host-parasite system Onchocerca ochengi in cattle, based on our previous findings in cattle exposed to challenge, that in vivo ivermectin attenuates the development of adult infections and that irradiation-attenuated L(3) induce significant protection. In a two-phase prospective study over 4 years, groups of cattle were exposed to severe natural challenge. In the first phase, 38/40 animals treated either with ivermectin or with moxidectin at either monthly or 3-monthly intervals had not developed detectable infections after 22 months of exposure whereas, in a non-treated control group (n = 14) nodule prevalence was 78.6% and the geometric mean (range) nodule load was 4.8 (0-33). In the second phase, all drug treatments were withdrawn, a new control group (n = 8) introduced, and exposure continued at the same site. After 24 months, all groups had developed patent infections, with geometric mean (range) nodule loads of 17.4 (4-99), 38.4 (10-111), 50.7 (26-86), 14.3 (0-69) and 14.7 (0-55) for the control, monthly-ivermectin, 3-monthly ivermectin, monthly moxidectin and 3-monthly moxidectin groups, respectively. There was no evidence of protection-indeed the 3-monthly ivermectin group was significantly (P < 0.05) hyper-susceptible. In addition, microfilarial densities and the rate of increase in microfilarial load were significantly higher (P < 0.05) in the ivermectin-treated groups than in control animals. These results have important implications for ivermectin-based control of human onchocerciasis and suggest that humans exposed to ongoing transmission in endemic areas whilst receiving ivermectin are unlikely to develop immunity and will be highly susceptible should drug distribution cease.

Animals↗

PubMed1987

Nematode antigens in protection, diagnosis and pathology.

A thorough study of parasite antigens is a prerequisite for control programmes based on protection by vaccination, accurate serodiagnosis and perhaps immune modulation to diminish pathological sequelae. Stage specific surface secreted and somatic antigens may be of particular value in proceeding towards these goals. The design of vaccines is most appropriately focused on surface antigens. With respect to pathology, certain antigens must stimulate humoral and, or cellular immune responses which are responsible for the undesirable immunopathologic consequences of the disease. The ultimate objective, therefore, is identification of those particular antigens followed by appropriate down regulation of the immune system in order to delete such potentially harmful immunological reactions. The relevant illustration presented in this context is an interesting correlation between one particular clinical condition of onchocerciasis ("sowda") and the serological response, defined both in terms of the parasite antigen and an immunoglobulin class restricted antibody response. Current parasitological methods of diagnosis consistently underestimate parasite prevalence. Failure to detect low level patent infections incurs the risk of having a reservoir capable of perpetuating infections. There is, then, an urgent requirement for accurate serodiagnosis, to be used in association with, and for the evaluation of, drug treatment and vector elimination in parasite control programmes. Given the high sensitivity of current immunoassay technology, the only bar to establishing the necessary immunological tests is the choice of suitably specific antibody-antigen systems. Once these are identified, a combination of recombinant nucleic acid biochemistry and hybridoma technology should provide the necessary reagents for inexpensive, robust and specific diagnostic tests. In addition, it may not be many years before the ubiquitous RIA and ELISA technology gives way to the newly developing biosensor systems. Finally, given the sensitivity and specificity of today's nucleic acid hybridization techniques, we may soon expect to see specific identification of infective larvae in their vectors of this, a cloned DNA probe specific for Onchocerca volvulus, and with potential for the detection of infective larvae in blackflies is described.

Animals↗

PubMed1988

Onchocerciasis and immunity in humans: enhanced T cell responsiveness to parasite antigen in putatively immune individuals.

To identify possible immune mechanisms in human onchocerciasis, we compared a group of 12 individuals who had no clinical or parasitological evidence of infection, despite ongoing exposure to the parasite, with a group of 16 individuals from the same area who had active Onchocerca volvulus infection. Despite having less parasite-specific serum antibody, the infection-free ("putatively immune") individuals showed greater lymphocyte responsiveness, especially interleukin-2 (IL-2) production, to O. volvulus antigen (OVA) than did the infected subjects; lymphocyte responses (including IL-2 production) to mitogens and nonparasite antigen in both study groups were equivalent and normal. Our findings define differences in parasite-specific T cell subpopulations between infected and putatively immune subjects that could be a central element in developing or maintaining protective immunity to O. volvulus infection.

Adolescent↗

PubMed1974

Onchocerciasis in Canada.

The first two cases of onchocerciasis seen in Canada are reported. The patients had come from West Africa to study in Canada several months prior to admission to hospital. The presenting symptom in each case was intense pruritus. One of the patients had early ocular involvement. The diagnosis was made by means of microscopic examination of a skin snip. The subcutaneous nodule excised from one of the patients showed the adult Onchocerca volvulus. Both patients also had urinary schistosomiasis. The clinical features, laboratory findings, treatment and public health aspects of onchocerciasis are discussed.

Adult↗

PubMed1981

The use of aceto-orcein-stained squash preparations for enumeration of nuclei in microfilariae of various filarial parasites.

The nuclear numbers of situated between the cephalic space and the nerve ring (CS-NR) in the microfilariae of six filarial species were examined. For the counting of nuclei, aceto-orcein squashing preparations were used. This procedure revealed nuclei clearly visible under the phase-contrast microscope. The mean number of nuclei in the CS-NR region was very similar between Brugia pahangi and B. malayi, but was statistically different between Onchocerca volvulus and O. gutturosa. In the microfilariae of O. volvulus, two types of nuclei were clearly shown in this region. The procedure described is useful in the anatomical study of microfilariae.

Animals↗