PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Onchocerca”

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 667 records · Page 37Linked to original sources
PubMed1988

Comparative effects of anthelmintics on motility in vitro of Onchocerca gutturosa, Brugia pahangi and Acanthocheilonema viteae.

The effects of standard anthelmintics on the motor activity in vitro of adult Onchocerca gutturosa, Brugia pahangi and Acanthocheilonema viteae were determined using a micromotility meter. Fresh adult males dissected from bovine tissues were the best source for observations on O. gutturosa. Parasites liber-ated by collagenase digestion showed poor viability and motility. Only segments of O. gutturosa females were obtainable by dissection and these were not able to sustain motility in vitro. Adult males and females of O. volvulus were active after collagenase digestion of human nodular tissue, but behaved so irregularly that satisfactory monitoring of their movements with the meter was not possible on a regular enough basis to permit quantitation of drug-induced changes. Inhibitory effects on motility of O. gutturosa, B. pahangi and A. viteae were produced by anthelmintics which showed macrofilaricidal effects in vivo in a laboratory rodent model, with the exception of the benzimidazoles. O. gutturosa was, however, much more sensitive than B. pahangi or A. viteae to the temporary paralyzing effects of levamisole and pyrantel. The utility of in vitro screening against O. gutturosa and B. pahangi was evaluated by determining the discriminatory capacity of the tests in detecting novel compounds with reproducible in vivo activity in the jird-B. pahangi/A. viteae model. The results suggested that this would be a valuable selective screening procedure. Although false positives were detected at the rate of 15-17% of the novel anthelmintic chemical series tested, no false negatives were allowed through the screen provided both O. gutturosa and B. pahangi were included.2=

Animals↗
PubMed1988

Cell-mediated immune responses in human infection with Onchocerca volvulus.

Mechanisms involved in modulation of the immune response in persons with chronic Onchocerca volvulus infection are poorly understood. In this study in vitro reactivity of PBMC to O. volvulus antigen (Ovag), streptolysin O (SL-O) and the mitogen PHA was tested in 62 infected individuals (INF), 17 persons living in the endemic area with exposure to the infection, but with no detectable infection (END), and 7 healthy controls (CTRL) in Liberia, West Africa. Mean blastogenic responses to Ovag were minimal and did not differ between the groups. There was, however, heterogenous reactivity to Ovag in the INF and END. For example, individuals with a history of therapy, and half of those less than 17 yr old who were tested, showed high responses. No significant differences in the response to SL-O or PHA were detected between the groups. IL-2 production in response to Ovag was minimal in the majority of infected subjects. Exogenous IL-2 was found to cause a significant increase in mean responses to Ovag and SL-O in INF and END only. Similarly, Ovag did not stimulate IL-1 production in most INF, whereas stimulation with LPS led to significantly greater production of IL-1. Depletion of plastic and nylon wool adherent cells did not increase responses to parasite-related antigen in INF, END or CTRL; however, responses to SL-O were augmented in INF, an effect that was also observed in CTRL. Finally, depletion of CD8 or CD16 cells in INF by C lysis did not increase blastogenic responses. These results indicate that cell-mediated immunity to parasite-related Ag as reflected in lymphocyte responses in vitro is diminished in infected individuals, and that this may be caused by defects in T cell activation.

Animals↗
PubMed1988

Onchocerca volvulus. Monoclonal anti-idiotype antibody as antigen signal for the microfilaricidal cytotoxicity of diethylcarbamazine-treated platelets.

Over the past 35 yr, diethylcarbamazine (DEC) has been the most widely used agent for the treatment of filarial diseases, particularly in onchocerciasis. The microfilaricidal action of DEC has been recently shown to be mediated by blood platelets with the additional triggering of a filarial excretory Ag (FEA). This FEA could be detected by using mAb in the serum of infected patients. By using one mAb (IA2(23] directed against Onchocerca volvulus and recognizing circulating Ag (Ab1), we purified by affinity chromatography the target molecule of IA2(23) (an O. volvulus glycoprotein recognized by IA2(23) mAb). This compound had a dose-dependent effect on the cytotoxic action of DEC-treated platelets. We subsequently produced an anti-idiotype mAb to Ab1 (Ab2), and considered the possibility of replacing the O. volvulus glycoprotein recognized by IA2(23) mAb by Ab2. Ab2 was selected according to its ability to inhibit the binding of radioiodinated Ab1 to the filarial target Ag. It induced the production of anti-O. volvulus antibodies (Ab3) in rats. At a constant concentration of DEC platelets, the addition of increasing amounts of Ab2 led to a dose-dependent cytotoxic effect against parasite larvae. Experiments performed with Ab2 on detergent solubilized surface proteins of platelets identified four bands of Mr 18, 26, 43.5, and 100 kDa, supporting the idea of the presence of binding sites on the platelets for a FEA required for the microfilaricidal cytotoxicity of DEC-treated platelets.

Animals↗
PubMed1988

Analysis of glutathione-enhanced differentiation by microfilariae of Onchocerca lienalis (Filarioidea: Onchocercidae) in vitro.

Reduced glutathione (GSH), but not its oxidized form (GSSG), stimulated development of Onchocerca lienalis microfilariae to the late first-larval stage in vitro. The degree and frequency of development was dose-related with a peak of activity at 15 mM, a concentration that is similar to known intracellular levels of GSH. To determine the mode(s) of action of this multifunctional compound, other reducing agents (L-cysteine, dithiothreitol), cysteine delivery agents (N-acetyl-L-cysteine, L-thiazolidine-4-carboxylic acid, L-2-oxothiazolidine-4-carboxylic acid), cysteine analogues (S-methyl-L-cysteine, D-glucose-L-cysteine, cysteine ethyl ester), free-component amino acids of GSH (glutamic acid, cysteine, and glycine), a specific metabolic inhibitor of gamma-glutamyl synthetase (buthionine sulfoximine), and an inhibitor of gamma-glutamyl transpeptidase (gamma-glutamyl glutamic acid) were also tested at concentrations of 0.01-50 mM in this system. N-acetyl-L-cysteine at 1-5 mM and D-glucose-L-cysteine at 2.5-10 mM significantly enhanced development. In contrast to those worms maintained in GSH-supplemented medium, microfilariae exposed to GSH for only the first 24 hr showed no enhancement by day 7 in culture. Neither buthionine sulfoximine nor gamma-glutamyl glutamic acid at 0.01-35 mM inhibited the effects of 15 mM GSH or 1 mM N-acetyl-L-cysteine. Results indicate that GSH or other cysteine analogues possessing a free sulfhydryl group must be present in the extranematodal environment to support microfilarial differentiation in vitro.

Animals↗
PubMed1987

Infection rates and parasitic loads of Onchocerca volvulus, and other filariae, in Simulium sanctipauli s.l. and S. yahense in a rain-forest area of Liberia.

Simulium sanctipauli s.l. and S. yahense are common and widespread in the rain-forest zone of Liberia, but differ with regard to their biting densities and contribution to the transmission of Onchocerca volvulus. Although, in a study area on the St. Pauli River, S. sanctipauli s.l. (presumably S. soubrense in the sense of Post) was the predominant ma-biting species (74.3% of 30,855 females examined), S. yahense was shown to be the important vector. While 1000 biting females of S. yahense carried 96 3rd stage larvae indistinguishable from O. volvulus, only 14 were found per 1000 females of S. sanctipauli s.l. Of the parous females (3135 S. sanctipauli s.l./1621 S. yahense) 23.8/39.9% harboured 1st and/or 2nd stage filarial larvae and 1.9/9.4% 3rd stage larvae of O. volvulus. Animal filariae of unknown origin, indicative of zoophily, were very common in S. sanctipauli s.l. (13.8%) but practically absent from S. yahense (0.5%). In spite of its poorer vectorial performance S. sanctipauli s.l. cannot be neglected as a vector because it may occur in high biting densities and contribute considerably to the transmission, in particular in the vicinity of the St. Paul River. The interplay of two vector species, which develop in different types of water-courses explains the overall high endemicity of onchocerciasis in the study area.

Animals↗
PubMed1987

Transfer of immunity to the microfilariae of Onchocerca lienalis in mice.

The model of Onchocerca lienalis microfilariae (mf) in CBA mice has been employed to examine the immunological mechanisms underlying the destruction of skin-dwelling mf in immunised hosts. Spleen cells from highly resistant donors transferred to naive, syngeneic recipients conferred significant protection against mf challenge, with up to 78% reductions in parasite recoveries. Levels of resistance afforded by adoptive transfers of immune cells were dose dependent and only significant above a threshold of 4 x 10(6) splenocytes. Mixed T and B lymphocytes elicited resistance in recipients, although neither cell population was protective alone. Immune serum evoked resistance to mf challenge by passive transfer, but only when collected shortly after booster immunisations of the donors. Xenogeneic sera from immunised rabbits or calves failed to confer protection to recipient mice. It is concluded that resistance to O. lienalis mf in mice is likely to be primarily governed by a thymus-dependent humoral response.

Animals↗
PubMed1987

Equine ocular pathology ascribed to Onchocerca cervicalis infection: a re-examination.

Eyes from 292 old (15-20 years) horses originating in the eastern, southeastern and midwestern United States were examined for the presence of Onchocerca cervicalis microfilariae (mf) and concurrently for anterior and posterior segment ocular pathological changes. One-hundred-fifty-three animals (52.4%) were positive for dermal mf (range 0.03-5,364/mg). Of these, 60 animals had anterior segment changes. An additional 58 animals with pathological changes had no dermal mf. Mf were recovered from the ocular tissues of 18% of animals (range 0.07-29/mg). All animals with ocular mf were positive for dermal mf. Lesions most frequently encountered were punctate scleral opacities (in 14.0% of horses--7.2% with mf), temporal scleral viteligo (in 11.6%--6.8% with mf) and uveitis (11.0% of horses--6.2% with mf). Few significant posterior segment changes were seen. These data suggest that no ocular pathological changes represent reliable indicators for the presence of O. cervicalis infection.

Animals↗
PubMed1986

Invasion of the mouse eye by Onchocerca microfilariae.

Onchocerca cervicalis microfilariae (mf) were injected s.c. into the scalp between the eyes of CBA/H mice. Invasion was followed by slit-lamp biomicroscopy and H & E stained serial sections at varying times post infection. The first mf observed were found 24 hr p.i. on the corneal surface in tear fluid. At 48 hr mf were observed actively swimming in the anterior chamber and by 3 d in the corneal stroma. Histologically mf appeared in orbital muscle connective tissue, subcutaneously in the eyebrows at the eyelid/conjunctiva junction from 6 hr p.i. By 12 hr some mf had moved into the suprascleral muscle junctions, the sclera and into the superior corneal stroma. By 24 hr mf were present in larger numbers in all these sites. Mf were found in all eyes up to 42 d p.i. No mf were seen in any sections of the retina or optic nerve. Rabbit antiserum raised to mf, used in an avidin-biotin immunostain to check whether mf might have been hidden within the retinal nuclear layers, revealed no mf although they were plainly seen in other ocular tissues. Retinal invasion was induced by injection of mf into the lateral tail vein: serial sections revealed mf associated with blood vessels in the sclera, suprascleral muscle blocks and inner plexiform layer of the retina from 5 min p.i.

Animals↗
PubMed1987

Studies of the growth-regulating effects of ivermectin on larval Onchocerca lienalis in vitro.

At concentrations of 0.1-100 ng/ml ivermectin inhibited L3-L4 molting by Onchocerca lienalis in vitro. The degree of inhibition was dose-dependent with a significant effect apparent at 0.1 ng/ml and complete inhibition occurring at 100 ng/ml. The ED50 for molt inhibition was 0.19 ng/ml. Molt-inhibiting levels of the drug were not acutely toxic to the worms. In the presence of 10 ng/ml, a concentration giving 95% molt inhibition, motility at day 7 postinoculation was 71% of that seen in nontreated controls. A more pronounced effect on motility was apparent in larvae under long-term cultivation in the presence of ivermectin. Kinetic studies indicated that the majority of the larvae respond irreversibly to the drug within the first 2 hr of exposure. Twenty-four hours of exposure were required for a maximal response. The inhibitory effects of ivermectin were less pronounced if larvae were allowed to develop under normal culture conditions for 24 or more hours prior to the initiation of drug treatment.

Animals↗
PubMed1987

Seasonal changes in density and tissue distribution of Onchocerca cervicalis microfilariae in ponies and related changes in Culicoides variipennis populations in Louisiana.

Seasonal changes in density and spatial distribution of Onchocerca cervicalis microfilariae were studied in ventral-midline skin of 15 infected pony mares in southern Louisiana. Triple running mean analysis of data over a 13-mo period indicated that a distinct pattern exists in total microfilariae population density and in microfilariae occurrence in different levels of the dermis. Microfilariae density reaches peak levels in the spring followed by a 58% decrease in the summer, a 19% increase in the fall, and a decrease to the lowest numbers in the winter. Microfilariae were found in all levels of the skin during the spring, summer, and fall but were not found in the superficial layers of the dermis during the winter months. The population density of Culicoides variipennis, a demonstrated vector of O. cervicalis, appeared to have seasonal fluctuations similar to the changes in microfilarial density. Harmonic wave analysis of microfilariae density data in individual ponies showed that all individuals did not follow the population trend.

Animals↗
PubMed1987

Failure of Onchocerca gutturosa to develop in Simulium soubrense and Simulium yahense from Liberia.

Laboratory reared female S. soubrense and S. yahense from Liberia were intrathoracically inoculated with bovine skin dwelling microfilariae of Onchocerca gutturosa. Of a total of 174 flies, each injected with 50 fresh microfilariae, the maximum development was to late first-stage larvae. One S. soubrense also contained two second-stage larvae and a maldeveloped third-stage larvae. No development to normal third-stage larvae was observed in any fly despite maintenance at 28 degrees C for up to 10 days following infection. This contrasts with complete development of O. volvulus in both blackfly species under similar conditions.

Animals↗
PubMed1986

Further studies on the resistance to Onchocerca microfilariae in CBA mice.

Various factors governing resistance to the microfilariae (mf) of Onchocerca lienalis in mice have been examined to provide baseline data for use of this model in immunological studies. The survival of mf during a primary infection followed a similar course in the skin from most anatomical regions of the body. Mice were highly resistant to secondary infections, manifested by parasite densities over the body that were reduced by 83-100% compared with controls. Recoveries of mf from the ears, used in later experiments, were a representative measure of parasite survival in other skin sites. The resistance to challenge induced by a primary infection was not dependent on the route of administration (intravenous, intraperitoneal, subcutaneous and intramuscular) of the latter and was apparently systemic. Primary infections of various durations that were chemically-abbreviated conferred maximum protection when of 15 days or longer (95-97%) and substantial resistance when of only 7 days (84%). Similar levels of protection were demonstrated in mice that were sensitized with single or multiply-divided mf doses, or challenged in a similar manner. Primary infections containing as few as 20 mf induced almost the same degree of protection (80%) as 50 to 10,000 mf (88-97%). Apparently, resistance to re-exposure with O. lienalis mf is mediated by a highly effective mechanism(s) in CBA mice.

Animals↗
PubMed1985

Onchocerca volvulus: transplantation of adult worms into chimpanzees.

Adult Onchocerca volvulus were transplanted into chimpanzees with or without complete or partial digestion of associated nodule tissue. Survival of adults worms was limited, but low level microfilarial densities remained detectable in skin over partially digested nodule transplants for 12 months. Human nodule tissue transplanted with adult worms showed enhanced survival as compared to subcutaneous tissue transplanted without worms. It is postulated that this reflects the action of an immunosuppressive factor utilized by the parasite to permit its own survival.

Animals↗
PubMed1985

Specificity of surface molecules of adult Brugia parasites: cross-reactivity with antibody from Wuchereria, Onchocerca and other human filarial infections.

The extent of structural and immunological similarity between surface antigens of three species of Brugia filarial parasites was studied by lodogen-mediated surface labelling of adult worms of B. malayi, B. pahangi and B. timori. The close homology and cross-reactivity between these antigens reported in previous surface labelling studies with Bolton-Hunter reagent, was verified in this system. The surface antigens of adult B. pahangi are also recognised by antibody from patients with Wuchereria bancrofti, the major human lymphatic filariae, and by antibody to Loa loa and Mansonella perstans. Further experiments have begun to establish the boundaries of these cross-reactions: antibodies to nonfilarial nematodes such as Trichinella, Necator and Strongyloides does not recognise the adult surface antigens; however, although most anti-Onchocerca sera show little or no reaction to the major (29 kDa) surface antigen, there is consistent reactivity to the secondary 20 kDa antigen, and extensive recognition of a minor antigen of 15 kDa.

Animals↗
PubMed1985

The Onchocerca volvulus micro- and macrofilarial responses in onchocerciasis patients to increased dosage of diethylcarbamazine.

The response of 45 severely infected onchocerciasis patients to relatively high doses of diethylcarbamazine citrate (DEC-C) has been determined. The treatment comprised two sequential phases; the first phase comprised the topical applications of a DEC-C lotion and of the anti-inflammatory steroid betamethasone. The second phase comprised the daily oral administration of high doses of DEC-C (30 mg/kg body wt) for seven days. Onchocerca volvulus microfilarial (o.v.mf.) counts in skin snips of the 45 patients decreased by 96 +/- 1.5% after 5 days of treatment with topical DEC-C lotion. Following the administration of oral DEC, the average O.v.mf. counts in the skin snips at days 51, 97, and 143 remained decreased by 85 to 93%. The mean O.v.mf. counts in 10 nodules excised from 5 treated patients at day 77 had decreased by 93% compared to the mean O.v.mf. counts in 11 nodules taken from 5 untreated patients with similar initial O.v.mf. infection. No visual loss resulted from the treatment.

Administration, Oral↗
PubMed1985

Calcification in adult Onchocerca volvulus.

Calcified worm fragments of adult Onchocerca volvulus from patients in West Africa were collected for a chemical analysis. The material contained predominantly calcium carbonate. Some results of investigations on the occurrence of calcified worms in untreated populations are reported on. Relations between the numbers of old parasites and those of calcified worms are discussed. The significance of possible resorption of calcified worm fragments for the interpretation of the effects of drug trials or other control measures are mentioned.

Animals↗
PubMed1985

Quantitative studies on the transmission of Onchocerca volvulus by Simulium damnosum s.l. in the Tukuyu Valley, South West Tanzania.

A survey of the Simulium breeding and the transmission of Onchocerca volvulus was carried out in and around the Tukuyu valley, S.W. Tanzania, S. damnosum s.l. was found breeding in the midstretches of the main rivers in the valley and their bigger tributaries, and also in the boundary river to Malawi and the most northerly of the three rivers draining the Livingstone Mts. to Lake Nyasa (L. Malawi). A total of 19,500 S. damnosum s.l. females was caught and 13,200 dissected. The annual biting rate varied between 2,000 and 23,800. 7.6% of all the flies were infected with O. volvulus and 1.5% carried infective larvae in the head capsule, on average 2.7 per fly. The transmission was mainly in the dry season and the annual transmission potential varied between 0 and 1,120. The entomological data showed many similarities to those from the Mahenge Mts., Tanzania, and correlation of places with comparable transmission potentials suggests a similarity in the relationship parasite-human host between the West African rain forest and the two Tanzanian foci.

Animals↗