Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Onchocerca”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 271 records · Page 15Linked to original sources
PubMed1995

Characterization of a novel non-muscle myosin-related protein from Onchocerca gibsoni.

A cDNA library was constructed in lambda gt11 using poly(A)+ mRNA from early larvae of Onchocerca gibsoni. Screening of the library using serum from a single onchocerciasis patient yielded several strongly immunoreactive clones, one of which (OGK2) was found to encode a novel myosin-related protein. cDNA clone OGK2 contained an insert of 2017 bp, consisting of continuous open reading frame in frame with the vector, hence this clone encodes 671 amino acid residues of a larger protein. A fragment (619 nt) of the OGK2 cDNA was subcloned into the expression vector pGEX-1N to generate a glutathione S-transferase fusion protein. Polyclonal antiserum raised to this fusion protein strongly recognised an O. gibsoni protein of approximately 220 kDa. Immunolocalization studies indicated that this protein was associated predominantly with the hypodermis and a number of other specific membrane layers in the adult parasite. Myosin-related proteins are frequently immunodominant parasite antigens and in a number of studies have been shown to confer a degree of protective immunity against the corresponding parasite. Evaluation of the protective potential of the OGK2 protein, therefore, appears to be warranted.

Amino Acid Sequence↗
PubMed1995

Mitochondrial alleles of Simulium damnosum sensu lato infected with Onchocerca volvulus.

Onchocerca volvulus infected Simulium damnosum s.l. were analysed by directed heteroduplex analysis. Of 73 infected flies, 68 produced heteroduplex products identical to those previously identified. All 6 major sibling species, except S. leonense, were present in this group. In the 5 remaining flies, 2 new heteroduplex patterns were noted. Molecular phylogenetic analysis of these samples suggested that they belonged to the S. squamosum/S. yahense subcomplex. The ability to reliably genotype adult flies will permit studies of the vectorial capacity of the sibling species of S. damnosum s.l. for the blinding and non-blinding strains of O. volvulus.

Alleles↗
PubMed1979

The use of an Onchocerca volvulus microfilarial antigen skin test in an epidemiological survey of onchocerciasis in Guatemala.

Onchocerca volvulus microfilariae obtained from onchocercal nodules were used as antigenic material for a skin test. This antigen is as specific as those previously employed in skin tests, detecting 85.2% of the persons with positive diagnostic signs of onchocerciasis in endemic areas. A low rate of false positives was found in the control group in nonendemic areas. The positive rate of reactions in the persons without positive signs in the endemic areas might be due to the presences of cases not detected as a result of palpation for nodules and two skin biopsies. In the examination of the residents of several populations, a close correlation was found between the positive rates of skin tests and the presence of infection. From these findings, we conclude that the skin test using the microfilarial antigen is a suitable procedure for the diagnosis of onchocerciasis. The skin test could also be useful as an epidemiological tool in assessing the effectiveness of control programmes.

Adolescent↗
PubMed1981

Seasonal variation in the microfilarial skin density of Onchocerca volvulus and in the biting activity of Simulium spp. in Guatemala.

The density of Onchocerca volvulus microfilariae in the skin of 11 carriers was examined by carrying out a monthly examination in a single endemic area of Guatemalan onchocerciasis. The results obtained suggested the possibility of a seasonal variation in the microfilarial skin density. Almost all of the volunteers participating had shown a peak concentration of microfilariae in September, followed by August or October. The highest biting densities of Simulium ochraceum, the principal vector of onchocerciasis in Guatemala, occurred from September to the following January. It thus appears that the seasonal variation in the microfilarial density may correspond, to some extent, with the biting activity of the vector, S. ochraceum and/or with climatic changes in the area.

Adolescent↗
PubMed1982

Separation of viable and non-viable Onchocerca microfilariae using an ion exchanger.

A technique has been developed for separating viable and non-viable Onchocerca lienalis microfilariae (mff) by passing a suspension of the parasites through a column of DEAE cellulose. A proportion (between 42% and 87%) of normally motile parasites, whether unfrozen or cryopreserved, passed through the cellulose columns and retained their viability. Non-motile and sluggish mff were retained by the cellulose. The proportion of viable cryopreserved mff was greater after passage through the column as assessed by motility, migration in mice and development in the insect vector. Numbers of cryopreserved mff eluted through the columns peak quickly at a relatively high level after about 20 ml of eluate had been passed through, whereas normal unfrozen parasites rose and fell in numbers more slowly. By using sodium chloride gradients and buffers of differing conductivity it was concluded that the separation of the mff is probably due to net charge changes as well as motility. It is believed that this technique offers considerable promise as a tool to provide populations of mff of more uniform viability following freezing and thawing with existing cryopreservation techniques.

Animals↗
PubMed1983

The distribution of the microfilariae of Onchocerca volvulus in the different body regions in relation to the attacking behaviour of Simulium damnosum s.l. in the Sudan savanna of northern Cameroon.

Densities of Onchocerca volvulus microfilariae in four volunteers with low to moderate infections were estimated at five body sites by paired skin snips. The landing of Simulium damnosum s.1. females on the body of these volunteers was recorded during 12 hours for six days. Most flies fed at the ankles (53% and 51%) and calves (28% and 27% respectively) in both the standing and sitting positions. The density of microfilariae in the skin was highest in the pelvic region (24.1 mf/mg) and relatively low in the calf (14.8 mf/mg) and ankle (1.0 mf/mg) regions. From the biting rate (females/body part) and the microfilarial density (mf/mg) a transmission index was calculated for the different body regions. This was highest for the calves showing that this part of the leg, if unclothed, accounts for the highest rate of contact (50 to 60% of total) between vector and parasite.

Animals↗
PubMed1984

Observations on adult Onchocerca volvulus maintained in vitro.

Adult Onchocerca volvulus were enzymatically isolated with collagenase from excised nodules and kept in TC medium 199 with Hank's salts supplemented with various sera. Male and female worms survived in the culture medium and 10% human serum on average for about 11 days (maximum 28 days) and 14.5 days (maximum 42 days). Up to 4,000 microfilariae were expelled by each female per day, but the production of new oocytes or development of embryos could not be observed in vitro.

Animals↗
PubMed1986

Onchocerca volvulus: enzyme polymorphism in relation to the differentiation of forest and savannah strains of this parasite.

Isozyme analysis was carried out on Onchocerca volvulus worms collected from Liberia, Ivory Coast, Burkina Faso and Sudan to see whether this technique could detect differences between forest and savannah populations of this parasite. A total of 243 forest and 189 savannah individual female worms were electrophoresed and stained for seven enzymes. Four showed some polymorphism, LDH, MDH, PGM and MPI and the other three, GAPDH, PEP and GPI were invariant. Statistical analysis of the results showed that the relative proportions of genotypes from within the different countries conformed to Hardy-Weinberg expectations. Pairwise comparisons of allele frequencies between countries showed that populations from Liberia and Ivory Coast had a very similar composition; there was some divergence between all the other pairs of populations and the genetic distance was calculated to summarize the degree of divergence. The number of loci examined was small and the genetic distances were within the range expected for separate geographical populations of the same species. The usefulness of this technique in worm identification is discussed.

Alleles↗
PubMedDate not supplied

Identification of the surface polypeptide antigens of the infective larvae of Onchocerca volvulus.

The surface polypeptide antigens of third-stage infective larvae (L3) and adult males of Onchocerca volvulus have been compared after iodogen-catalysed radioiodination, separation by sodium dodecyl sulphate-polyacrylamide gel electrophoresis in beta-mercaptoethanol followed by autoradiography. L3 surfaces contained polypeptides with apparent molecular weights of 14, 18.5, 26, 34, 51, 68 and 130 kDa, whereas the adults contained 14, 19, 26, 34, 37.5 and 68 kDa components. By immunoprecipitation with patient's sera, only the 14 and 18.5 kDa components were shown to be antigenic on the L3, the other components being unreactive with patients' antibodies. Under similar conditions, 4 of the 6 adult male polypeptides reacted with patients' antisera, confirming their antigenic nature. Lentil lectin and immunosorbent chromatography of the surface components revealed the 18.5 kDa and 68 kDa antigens of L3 and adult males respectively to be glycoproteins. The apparently weak reactivity of L3 surface components with host antibody may be part of an escape mechanism that favours the establishment of O. volvulus in human hosts.

Animals↗
PubMedDate not supplied

Serum-dependent interaction of granulocytes with Onchocerca volvulus microfilariae in generalized and chronic hyper-reactive onchocerciasis and its modulation by diethylcarbamazine.

The adherence and cytotoxicity of granulocytes to microfilariae of Onchocerca volvulus were examined in vitro. Reactivity and modulation by diethylcarbamazine of isolated eosinophilic and neutrophilic granulocytes from patients with generalized and chronic hyper-reactive onchocerciasis (sowda or localized form) from endemic foci in Liberia were evaluated under varying serum conditions. In the presence of pooled sera from patients with generalized onchocerciasis granulocytes from both polar groups of patients exhibited similar adherence rates, whereas immobilization rates were higher for eosinophils than for neutrophils. In localized onchocerciasis, the use of autologous serum resulted in a significant decrease in adherence and immobilization rates for both eosinophils and neutrophils. After preincubation of eosinophils, but not of microfilariae, with diethylcarbamazine autologous serum-mediated adherence and cytotoxicity were enhanced to rates similar to those found with pooled serum from individuals with generalized onchocerciasis. These results suggest that granulocytes from both forms of onchocerciasis did not differ with respect to their anti-parasitic reactivity and that antibodies as well as additional serum factors appear to contribute to the functional activity of these effector cells. The findings indicate that predominantly eosinophils, compared to neutrophils, damage the larvae of O. volvulus and support earlier observations which suggest that diethylcarbamazine influences the effector cells rather than the parasite itself.

Adolescent↗
PubMedDate not supplied

The effects of ivermectin used in combination with other known antiparasitic drugs on adult Onchocerca gutturosa and O. volvulus in vitro.

The effects of ivermectin at a concentration of 3.13 x 10(-6) M used in combination with other antiparasitic drugs on the viability of adult Onchocerca in vitro were assessed using MTT colorimetry and worm motility levels. When ivermectin was used against male O. gutturosa over a 7 d period in combination with suramin (5 x 10(-5) M), CGP 6140 (3.13 x 10(-6) M), CGP 20376 (1.95 x 10(-7) M), mefloquine (3.13 x 10(-6) M), levamisole (3.13 x 10(-6) M), mebendazole (5 x 10(-5) M), flubendazole (5 x 10(-5) M) and albendazole (5 x 10(-5) M), there was either no increased effect or only a marginally increased effect on motility levels when compared with the use of ivermectin alone. MTT colorimetry revealed that in most cases there was a cumulative effect of the 2 drugs used in combination but not a synergistic effect. In a trial extended to 26 d it was demonstrated that the combination of ivermectin and suramin did not produce a greater inhibition of motility than ivermectin alone. Using female O. volvulus, the activity of ivermectin, CGP 6140 and the 2 drugs combined was examined. The motility of all 3 groups exposed to drug(s) was suppressed by 24 h compared with controls. MTT colorimetry performed on day 7, using the pre-weighed anterior end of each worm, illustrated that ivermectin alone produced a 43.4% inhibition of formazan formation compared with controls, CGP 6140 alone produced 50.6% inhibition, while the drug combination produced a 72% inhibition, equivalent to the heat-killed control.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Onchocerciasis in Malawi. 1. Prevalence, intensity and geographical distribution of Onchocerca volvulus infection in the Thyolo highlands.

Skin snips from 23,373 persons living in the Thyolo (formerly Cholo) highlands focus of southern Malawi showed infection with Onchocerca volvulus to be unevenly distributed within the highland area. In the centre of the focus most adults were infected, though intensity of infection was light, not exceeding a geometric mean of 8 microfilariae per mg of skin. It was estimated that 327,000 persons live in areas where prevalence of infection exceeds 10% and, of these, 94,500 persons over the age of one year are infected with O. volvulus. There is a significant relationship between infection with O. volvulus and bilateral blindness in the Thyolo focus, although the number of persons blind from onchocerciasis is probably less than 300.

Adolescent↗
PubMedDate not supplied

The effect of antimalarial chloroquine therapy and prophylaxis on concurrent infection with Onchocerca volvulus in Ecuador.

The effect of chloroquine phosphate on Onchocerca volvulus in vivo was studied in Ecuadorians undergoing treatment for malaria. All persons with a diagnosis of acute malaria and treated with 2500 mg of chloroquine over 3 d showed a 100% reduction of dermal O. volvulus microfilariae 7 d after treatment. However, 28 d after treatment the microfilarial densities returned to their pre-treatment levels and at 35 d they had increased to 121.6% of their pre-treatment values. Treatment did not appear to have any effect on the adult O. volvulus examined histologically in extirpated nodules. Patients treated for acute malaria and subsequently kept on a prophylactic regimen of 500 mg chloroquine weekly showed a reduction of 56.7% from pre-treatment microfilarial density after 27 weeks. Patients who underwent nodulectomy as well as treatment for acute malaria and were given 500 mg of chloroquine prophylactically for 27 weeks showed a reduction in dermal microfilarial density of 93.6%. Symptoms of onchocerciasis were reduced in the latter group of patients, with the elimination of all acute dermatological changes within 6 weeks. Ocular examination of these surgically and chemotherapeutically treated individuals revealed reductions of 94.9% of microfilariae in the anterior chamber, 95.9% of live microfilariae in the cornea, and 95.1% of dead microfilariae in the cornea. There was a reduction of 69.8% in corneal fluffy opacities. No alteration in the visual acuity or in visible lesions in the posterior segment was recorded. The results suggest that a complex interaction between chloroquine and O. volvulus takes place in vivo, which can be beneficial to the patient over a long period.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMedDate not supplied

Comparison of the sensitivity of different geographical isolates of Onchocerca volvulus microfilariae to ivermectin: effects of exposure to drug on development in the blackfly Simulium ornatum.

Four geographical isolates (Ghana forest, Ghana savannah, Cameroon forest, Guatemala) of Onchocerca volvulus microfilariae (mf) and O. lienalis mf (UK) were examined for their sensitivity to ivermectin by incubation in vitro in drug followed by assessing their ability to develop in the blackfly Simulium ornatum after intrathoracic injection. Parasites were incubated for 30 min in ivermectin (10(-6) to 10(-9) M), which resulted in a concentration dependent decrease in the numbers of parasites surviving and developing in the insect; there were significant reductions in parasite recoveries from all isolates in the 10(-6) M to 5 x 10(-8) M ivermectin groups, but no significant effect was seen following incubation in concentrations of 10(-8) M and below. Experiments consistently demonstrated that the 4 isolates of O. volvulus were similarly sensitive to ivermectin (in the 10(-7) M ivermectin groups there was a reduction of 76.3% to 85.1% in numbers of infective larvae, and 60.9% to 85.5% in numbers of all larval stages, compared to controls); O. lienalis mf were significantly more sensitive (100% reduction in infective larvae, 98.7% reduction in all larval stages). This baseline information on drug sensitivity and techniques should prove useful for examining populations of O. volvulus for possible development of drug resistance in the future.

Animals↗
PubMedDate not supplied

The effect of ivermectin treatment on the antibody response to antigens of Onchocerca volvulus.

The effect of the microfilaricidal drug ivermectin on the antibody response to a detergent extract of adult Onchocerca volvulus (OvAg) and a number of specific recombinant peptides was examined. Three of the peptides were combined in a serodiagnostic 'cocktail' and the effect of ivermectin on the diagnostic performance of this assay was assessed. Immunoglobulin (Ig) G1 serum levels in response to OvAg significantly decreased following ivermectin treatment. The antibody response to only one recombinant peptide (OvMBP29) was significantly affected, with IgG levels decreasing following treatment. Levels of total IgE increased following treatment. No correlation was observed between initial antibody level (or change in antibody level) and any adverse reaction to treatment. The serodiagnostic 'cocktail' was 100% sensitive before and after the use of ivermectin. A serodiagnostic assay using specific recombinant peptides can be used to evaluate infection in the absence of dermal microfilariae in areas where ivermectin is used.

Adolescent↗
PubMedDate not supplied

Immunodiagnostic studies on Onchocerca volvulus and Mansonella perstans infections using a recombinant 33 kDa O. volvulus protein (Ov33).

A total detergent-soluble extract of adult female Onchocerca volvulus (OvAg) and a recombinant O. volvulus protein (Ov33) linked to glutathione-S-transferase (GST) were compared with regard to their serodiagnostic suitability for differentiating between O. volvulus and Mansonella perstans infections in a region endemic for both filarial worms in western Uganda. Using OvAg in an enzyme-linked immunosorbent assay (ELISA), 98.8% sensitivity was obtained examining 84 O. volvulus microfilariae (mf) carriers living in the hyperendemic area. However, 5 of 18 (28%) sera from M. perstans mf carriers without O. volvulus mf, from another area hypoendemic for O. volvulus, cross-reacted with OvAg. Using the recombinant antigen Ov33-GST in an ELISA and Western blot assay, sensitivity for O. volvulus remained high (97.2% and 98.8% respectively) while none of 90 sera from M. perstans mf carriers reacted positively. Both antigens were used to examine a batch of sera from 260 persons living in the onchocerciasis hyperendemic area who did not have mf in their skin snips (9.5% of 2728 persons examined); 116 of these sera (44.6%) were positive in the OvAg ELISA, compared to 85 (32.7%) and 69 (26.5%) which were positive in Ov33-GST ELISA and Ov33-GST Western blot, respectively. Reaction with GST alone was minimal. The recombinant antigen Ov33 efficiently differentiates between O. volvulus and M. perstans infections, and is sensitive when used to detect patent and prepatent or low-level O. volvulus infections.

Animals↗
PubMed1983

Equine complement activation as a mechanism for equine neutrophil migration in Onchocerca cervicalis infections.

Extracts of Onchocerca cervicalis, an equine parasite, were incubated with radiolabeled equine neutrophils and neutrophil migration was assessed for factors derived from the parasite itself or for host-derived factors after incubation of these same parasite extracts with equine serum. No stimulus for cell migration was observed in saline extracts of adult worms, uterine microfilariae, or skin microfilariae at any dosage tested. However, after incubation of saline extracts with fresh normal equine sera a marked stimulus for neutrophil migration was observed. Ablation of this biologic activity was noted if equine serum had been pretreated with 10 mM EDTA or heated at 50 and 56 degrees C for 30 min. However, if equine serum was treated with 10 mM EGTA, made 10 mM with respect to Mg2+ ions, no reduction in neutrophil migration was noted, thereby suggesting that the equine alternative complement pathway was the means of generating the serum-derived neutrophil migration stimulus. Preliminary gel filtration of the activated equine serum suggested that although there was a neutrophil stimulus associated with a C5a-like molecule, other complement or serum components could be involved.

Animals↗