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 433 records · Page 24Linked to original sources

PubMed1975

Reactions to subconjunctival inoculation of Onchocerca volvulus microfilariae in pre-immunized rabbits.

Rabbits, pre-immunized by intravenous inoculations of live, or of freeze-killed microfilariae of Onchocerca volvulus, were later challenged by subconjunctival inoculation of live microfilariae. Those pre-immunized with live microfilariae showed a marked chemotic conjunctivitis and reactions in the cornea (stromal keratitis and limbal abscesses), starting within one day of challenge. They were classed as sensitized. Those pre-immunized with dead microfilariae produced minimal reactions also starting on day 1, and were classed as tolerant. Histologically the reactions were distinctly greater in sensitized than in tolerant animals. The predominant cells in the inflammatory exudate were polymorphonuclear leucocytes and lymphocytes. The immunological basis for the differences between sensitized and tolerant rabbits is discussed, together with its possible bearing on human onchocerciasis. The effects of long-term subconjunctival and sclerocorneal inoculation of microfilariae were compared in one sensitized, one tolerant, one previously exposed, and one sensitized control rabbit. The sensitized test animal showed lesions resembling the sclerosing keratitis of human onchocerciasis. Immature microfilariae taken from intra-nodular fluid showed little ability to penetrate the cornea of the rabbit, and were minimally pathogenic.

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↗

PubMed1986

Detection of serum antibodies and circulating antigens in a chimpanzee experimentally infected with Onchocerca volvulus.

The course of the humoral immune response was followed in a chimpanzee experimentally infected over 27 weeks with a total of 168 Onchocerca volvulus 3rd-stage larvae obtained from naturally infected wild-caught blackflies. Antibodies against an adult worm extract could be detected by ELISA from week 16 onwards (after the inoculation of 44 larvae). Peak antibody levels were observed between weeks 66 and 74 (about one year after the last larval injection). Thereafter, antibody levels markedly decreased but rose again after week 120. First microfilariae could be detected from week 124 onwards. Microfilarial counts remained low (not more than two microfilariae per skin snip) until the end of the observation period. High levels of IgM antibodies against adult O. volvulus antigens were detectable between weeks 26 and 80 by ELISA. Total IgE levels were found to be only marginally elevated during the course of the infection. Circulating parasite antigens were only detectable for a short time (weeks 34 to 44) of the prepatent period by immuno-radiometric assays (IRMAs) using monoclonal antibodies which were raised against O. gibsoni eggs. Competitive radio-immuno-assays detected host antibodies inhibiting binding of 125I-labelled monoclonal antibodies to parasite antigens from week 28 onwards. Host antibodies clearly interfere later in infection with the detection of circulating antigens.

Animals↗

PubMed1989

Prevalence, intensity and ocular manifestations of Onchocerca volvulus infection in Dimbelenge, Zaire.

In the zone of Dimbelenge (West Kasai region), Zaire we studied the prevalence, intensity and ocular manifestations of Onchocerca volvulus infection. We used the cluster sampling method to draw a sample of 327 people from a total population of 17,870. The prevalence of microfilaria in skin snips was 82.1% in people 20 years of age and older. The Community Microfilarial Load was 3.5. Blindness in 12 of 13 adults (92.3%) was caused by onchocerciasis. The rate of onchocercal blindness in the adult population was 5.1%. Twenty-four percent of adults had retinal changes as a result of onchocercal infection.

Adolescent↗

PubMed1981

Inhibition of NADP-linked malic enzyme from Onchocerca volvulus and Dirofilaria immitis by suramin.

NADP-linked malic enzyme (malate dehydrogenase (oxaloacetate-decarboxylating) NADP+, EC 1.1.1.40) has been partially purified from adult Onchocerca volvulus and Dirofilaria immitis. Suramin was found to inhibit the activity of malic enzyme from both filarial worms. The inhibition constants for suramin were calculated to be 0.011 microM and 0.015 microM for the enzymes from O. volvulus and D. immitis, respectively. In the case of NADP-linked malic enzyme from Trypanosoma brucei and chicken liver the inhibition by suramin was less pronounced. The inhibition constants were found to be 0.8 microM and 2.5 microM for the protozoan and vertebrate enzymes, respectively. The type of inhibition was competitive with respect to malate. The Michaelis constants for malate and pyruvate were determined to be 0.9 and 4.5 mM for O. volvulus and 0.85 and 5.0 mM for D. immitis, respectively. The low Km values for malate compared to those for pyruvate and the about 15-fold greater turnover in the direction of decarboxylation compared to carboxylation indicated that malic enzyme from both filarial sources might be involved in an alternative pathway leading from phosphoenolpyruvate via oxaleacetate, malate and pyruvate to lactate. It is suggested, that the inhibition of malic enzyme activity from O. volvulus by suramin might interfere with the generation of NADPH for biosynthetic reactions.

Animals↗

PubMed1988

Emergence of Onchocerca volvulus microfilariae from skin snips before and after treatment of patients with ivermectin.

As ivermectin is supposed to have a paralyzing effect, the emergence of Onchocerca volvulus microfilariae from skin snips before and after treatment was examined. Before treatment 79.8% of the microfilariae emerged from the skin snips. Three days after treatment the microfilarial skin density had dropped to 83% (placebo), 28% (100 microgram/kg ivermectin), 19% (150 micrograms/kg) and 14% (200 micrograms/kg) of the pretreatment values but the microfilarial emergence was not altered distinctly. The majority of the remaining microfilariae were mobile and able to leave the biopsy. Only a slight, but significant, dose-dependent trend of reduced emergence could be shown. From our results no direct support is derived for the hypothesis that O. volvulus microfilariae are paralyzed or immobilized by ivermectin.

Analysis of Variance↗

PubMed1990

Cloning of specific diagnostic antigens of Onchocerca volvulus.

Specific, serological diagnosis is one of the main goals in onchocerciasis research. To date this objective has been hampered by (a) scarcity of parasite material, and (b) antigenic cross-reaction between Onchocerca volvulus and other nematode species. In order to obtain specific antigens, and in amounts suitable for study, molecular biological techniques have been adopted. A lambda gt11 cDNA expression library prepared from O. volvulus adult female worms was screened using infected human sera from onchocerciasis patients and rabbit hyperimmune sera raised against Onchocerca and genus-specific Onchocerca antigen extracts. Five clones were selected and their inserts expressed as beta-galactosidase fusion proteins. The fusion proteins were examined using individual sera from patients with O. volvulus or Wuchereria bancrofti infections. Three of the fusion proteins were recognised by more than 80% of O. volvulus sera and exhibited weak reactivity with a few W. bancrofti sera. One of these three clones was recognised to a significantly greater degree by sera from sowda than from generalised onchocerciasis patients.

Animals↗

PubMed1981

Selective recovery of living microfilariae from Onchocerca volvulus nodules. Determination of optimal conditions for their culture in vitro for excretory/secretory products.

A method for the selective recovery of living microfilariae from Onchocerca volvulus nodules is described. The microfilariae migrate through solidified agar gel into overlayering Hanks balanced salt solution (HBSS). The highest recovery rates of the worms were obtained with 0.3 and 0.4% agar. Optimal conditions for in vitro cultures of the larvae in HBSS were established; pH range 7.0-7.5, glucose concentration 2-5 mg/ml for long term cultures, osmolality 200-309 mOsmoles/l, temperature 4 degrees C for prolonged cultures and 24-28 degrees C for overall best yield of excretory/secretory products (ESP). Subculturing of the larvae reduced contamination of ESP with human serum protein to minimal amounts after 9 recultures done within 96 h.

Animals↗

PubMed1988

Experimental interstitial keratitis induced by Onchocerca volvulus antigens.

To elucidate the pathogenic mechanisms involved in onchocercal sclerosing keratitis in humans, we developed a model of onchocercal interstitial keratitis in guinea pigs. Onchocerca volvulus antigens injected intrastromally into corneas of preimmunized Hartley guinea pigs induced an intense stromal keratitis with corneal edema, neovascularization, and infiltration with acute and chronic inflammatory cells. This reaction subsided after two weeks. Repeated intrastromal injection resulted in an exacerbation of the keratitis and ultimately in residual scarring. These findings are consistent clinically and histopathologically with the chronic interstitial keratitis observed in humans. To define which antigens induce the corneal reaction, O volvulus antigens were separated by molecular sieve chromatography and injected intrastromally. The highest activity was shown to reside in the fraction containing molecules of intermediate molecular weight. This model will be useful in defining O volvulus antigens and their role in sclerosing keratitis as well as in elucidating the immune mechanisms involved.

Animals↗

PubMed1981

Seasonal occurrence of Simulium ochraceum, the principal vector of Onchocerca volvulus in the southeastern endemic area of Guatemala.

Investigation of the seasonal occurrence of Simulium ochraceum, the principal vector of the Guatemalan strain of Onchocerca volvulus, were made from August 1978 until January 1980 in the upper reaches of the two main rivers of endemic onchocerciasis in Escuintla, Guatemala. The results showed that in the late dry season S. ochraceum larvae were restricted to permanent streams at intermediate altitudes. During the rainy season, though, the preimaginal sites of this black fly extended to the upper reaches of the numerous small intermittent streams due to partial subterranean flows. Seasonal occurrence of S. ochraceum in these temporary streams was observed throughout the wet season. However, this was most pronounced during the early months of the dry season (October-December) as long as these streamlets continued to flow. The adult population along the headwaters of these two rivers showed a high peak from October-December. This represented a pattern distinct from that of other places where the preimaginal sites of S. ochraceum occurred mostly in larger perennially running streams. The implications which the present findings have for any future larvicidal control program on the onchocerciasis-endemic region of Guatemala are discussed.

Animals↗

PubMed1984

The effects of diethylcarbamazine, mebendazole and levamisole on Onchocerca volvulus in vivo and in vitro.

The effects of mebendazole, levamisole, diethylcarbamazine citrate (DEC-C), and the combination of mebendazole and levamisole, on adult Onchocerca volvulus and on the in utero development of microfilariae was studied in nodules excised from patients in Southern Mexico. Adult worms isolated from patients treated with mebendazole showed a reduction in mobility and contained 40 times fewer developing microfilarial forms than did worms from untreated patients. Most of the developmental forms found in adult worms from mebendazole-treated patients were either oocytes or early morulae, with more mature forms being scarce or morphologically abnormal. Treatment with levamisole had a similar effect on embryogenesis, however it was much less marked. The number and distribution of developing forms in worms from patients treated with DEC-C was similar to that found in the control groups. The effect of the same three drugs on microfilariae in vitro was also tested. DEC-C at concentrations of 0.5 microgram - 2000 micrograms/ml did not have any obvious effect on motility or morphology of the worms provided the pH was maintained at physiological levels; levamisole also had no effect in vitro. Mebendazole induced the death of microfilariae when used at concentrations greater than 100 micrograms/ml, however these levels are greater than those found in the blood of patients under treatment. The optimal conditions for short-term maintenance of O. volvulus microfilariae in culture, are discussed. It is apparent from these studies that mebendazole has an effect on the maturation of microfilariae in utero and may also, at high concentrations, have a direct effect on mature microfilariae.

Animals↗

PubMed1968

The intake and transmissibility of Onchocerca volvulus microfilariae by Simulium damnosum fed on patients treated with Diethylcarbamazine, suramin or Mel W.

The best hope for the control of transmission of Onchocerca volvulus over much of Africa lies in combining larvicidal measures directed against the Simulium vectors with chemotherapeutic measures designed to reduce the reservoir of transmissible microfilariae in man.There are few drugs effective against O. volvulus. Diethylcarbamazine kills the microfilariae but has virtually no effect on the adult worms. Suramin kills adult worms and many, but not all, of the microfilariae. Mel W kills adult worms but has little or no action on microfilariae. All these drugs suffer at present from disadvantages of toxicity, which tend to limit their use on a mass scale in the field. Nevertheless, before they, or indeed any new drugs with similar actions on the parasites, can be used intelligently for the control of onchocerciasis transmission, it is necessary to have accurate quantitative information on the effect that each of them has on the microfilarial population available for intake by Simulium, as well as on their actions on the developmental potential of those microfilariae ingested by the flies.The present paper describes the effects of treatment with various courses of diethylcarbamazine, suramin or Mel W on the numbers of microfilariae ingested by groups of S. damnosum and on the numbers of infective larvae developing therefrom.

Arsenicals↗

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↗

PubMed1983

Development of Onchocerca volvulus from cryopreserved microfilariae in three temperate species of laboratory-reared blackflies.

Three species of British blackflies, Simulium ornatum s.l., S. erythrocephalum and S. lineatum, were infected with the cryopreserved microfilariae of Onchocerca volvulus obtained from human skin-snips in the Sudan. Doses of 5 or 10 microfilariae per fly were administered by intrathoracic injection into females, 1-2 days after eclosion from pupae. After 7 days at 27.5 degrees C and 85% relative humidity, microfilariae had completed development to third-stage larvae. Fly survival rates were highest for S. ornatum (96%) and lowest for S. lineatum (56%), and fell only marginally in each species when the larger dose of microfilariae was given. Infection rates ranged from 42% in S. lineatum up to 58% in S. ornatum following the lower dose of microfilariae, and 58% in S. lineatum up to 79% in S. ornatum following the higher dose. The proportion of microfilariae which completed development was relatively constant in each species of fly, ranging from 3.1-4.2% in S. lineatum to 10.5-16.8% in S. erythrocephalum. The greatest number of third-stage larvae recovered came from S. erythrocephalum at the higher dose of microfilariae, with a mean of 2.4 larvae per infected fly. As S. erythrocephalum has been successfully colonized through several generations in the laboratory, it is concluded that this is a promising species for reselection for increased susceptibility to O. volvulus.

Animals↗

PubMed1980

Serologic studies on onchocerciasis in Guatemala using fixed-tissue sections of adult Onchocerca volvulus.

Sera from 458 residents of a coffee plantation in an area of Guatemala endemic for onchocerciasis were examined for the presence of antibodies to Onchocerca volvulus using a fluorescent antibody (IFA) test with sections of adult worms as the antigen. Antibody response increased with age of the residents and microfilarial density. A total of 70.0% of the residents were serologically positive and 65.1% were positive for microfilariae. Males had higher microfilarial densities and higher IFA responses. Sixty-three individuals were positive for microfilariae and IFA-negative indicating a lack of sensitivity on the part of the test antigen. Seventy-four individuals were negative for microfilariae and IFA-positive, suggesting the possible usefulness of the test in the determination of present or past infection in the absence of microfilariae.

Adolescent↗

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↗

PubMed1978

Ultrastructural characterization of the cuticle of Onchocerca volvulus microfilaria.

Previous ultrastructural studies on various microfilariae have suggested the presence of a trilaminar membrane at the parasite cuticle. In the present report, the formation of the cuticle of Onchocerca volvulus microfilariae was studied at different developmental stages by transmission electron microscopy of samples obtained from subcutaneous nodules of untreated patients. The cuticle is formed by the layering of surface coat fibrillar components of the hypodermal cells. No plasma membrane is found at the cuticle of the microfilaria. The use of freeze-fracture replication confirmed the absence of a classic plasma membrane at the parasite cuticle. Our results suggest that immunogenic determinants of the microfilaria cellular elements are hidden from the exterior by the acellular cuticle. This may explain the lack of cellular reaction usually found around living O. volvulus microfilariae in the dermis of onchocerciasis patients.

Animals↗

PubMed2003

Human immune responses to infective stage larval-specific chitinase of filarial parasite, Onchocerca volvulus, Ov-CHI-1.

BACKGROUND: Ov-CHI-1 is a chitinase specifically expressed in the infective stage larvae of the human filarial parasite Onchocerca volvulus. Evidence has show that it could be a vaccine candidate, however, there is no data available regarding the immunological status of people naturally exposed to infective stage larvae and thus provoked by this antigen. METHOD: We analysed the Ov-CHI-1-specific immune response present in four endemic foci of human onchocerciasis (Ecuador, Nigeria, Togo and Cameroon) by enzyme-linked immunosorbent assays and T-cell proliferation assays. RESULTS: In these foci of infection, antibodies to Ov-CHI-1 were found to be present in only 22% of individuals from Ecuador, but were detected in 42-62% of infected individuals in the three foci from West Africa (Nigeria, Togo and Cameroon). There was found to be no relationship between antibody level and age, gender, or infection intensity as indicated by microfilarial density and numbers of skin nodules. The isotype response to Ov-CHI-1 was dominated by the presence of IgG3, IgG1 was present to a lesser extent. Our results show a positive correlation between N- and C-termini of Ov-CHI-1 in their ability to provoke humoral and cellular immune responses in the human. Peripheral blood mononuclear cell (PBMC) proliferative responses to Ov-CHI-1 when assayed, were found to be significantly higher in the individuals from endemic areas and there was a statistically elevated response to Ov-CHI-1 in the infected individuals when compared to putative immune individuals. CONCLUSION: Ov-CHI-1 is an antigen that we have found strongly induces both humoral and cellular immune responses in humans.

Journal Article↗