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PubMed1983

Onchocerciasis in Benue State of Nigeria III: a study of bionomics of Simulium damnosum (Theobald) complex at Manor.

Results of a 12-month study (January-December 1981) on the breeding sites, incidence and infection rates of Simulium damnosum in an area of Benue State of Nigeria endemic for human onchocerciasis are given. Natural and artificial breeding sites are described. Permanent and temporary breeding sites were recognized along the rivers in the study area and the intensity of rains was found to be the only factor which determined the permanency or temporary nature of a breeding site. All adult blackflies caught were S. damnosum "sensu lato" Greater numbers were caught during the rains with peak catches corresponding with peak of rainfall in September. The influence of shade temperature on daily biting activity was shown, peak activity being recorded at periods of day when temperature was low. Population density of blackflies increased with increasing distance from the main breeding sites on the river during the normal rains; at the peak of rains, the reverse was observed. April and September were the months of highest and lowest infection rates respectively among the catches while April to July were the most favourable period for onchocerciasis transmission because of the high infective bites per person per day in those months. The infective bites per person per day were estimated at 0.83 which, by comparison with values from endemic areas of Africa, confirmed the endemicity of the study area for human onchocerciasis. Dissected flies carried low number of developing larvae of Onchocerca volvulus with a mean of 3.9. Measurements of larvae are given and the relevance of the results to the epidemiology of human onchocerciasis in the study area is discussed.

Animals↗
PubMed1997

Production of monoclonal antibodies against excretory-secretory products of adult male Onchocerca gibsoni.

Nine monoclonal antibodies (mabs) have been produced against excretory-secretory products (ES) of adult male Onchocerca gibsoni. These mabs fail to interact with the highly cross-reactive phosphorylcholine (PC) group and with ES of the related rodent filarial parasites Acanthocheilonema viteae and Litomosoides carinii. Eight of the mabs are of the IgG isotype: 1 is an IgM. Three of the mabs, OGMES 4, 9, and 10, were each found by immunoprecipitation/SDS-PAGE analysis of [3H] leucine-labeled ES, to recognize a triplet of polypeptides of molecular weight 120, approximately 210, and approximately 260 kDa. No recognition was observed by any mab when [3H] glucosamine was employed as the radiolabel for ES. Western blotting employing [125I] as indicator system demonstrated that OGMES 7 recognized a molecule of 27 kDa, and OGMES 1, a molecule of approximately 210 kDa, albeit faintly. These mabs may be of value to researchers working on the isolation, characterization, and detection in the bloodstream of Onchocerca volvulus ES.

Animals↗
PubMed1986

Studies on a filarial antigen with collagenase activity.

We examined the ability of two filarial species, Onchocerca volvulus and Brugia malayi, to solubilize collagen molecules from native collagen fibrils. Collagenolytic activity was detected in extracts of adult worms, in living microfilariae of O. volvulus and in live infective larvae and adult female worms of B. malayi. Excretion-secretion factors produced in vitro by infective larvae of B. malayi also contained large amounts of collagenase. Studies with enzyme inhibitors suggest that the latter may be a metallo-protease. Antibodies to filarial collagenase were present in sera from patients with onchocerciasis and brugian filariasis and from mice immunized with B. malayi. These antibodies and a monoclonal antibody raised against O. volvulus antigens immunoprecipitate filarial collagenase but appear not to be directed against the active site of the enzyme.

Animals↗
PubMed1994

Biosynthetic radiolabelling of excretions-secretions of adult male Onchocerca gibsoni.

Maintenance of adult male worms of the bovine filarial parasite Onchocerca gibsoni in vitro, in the presence of radioactive precursors, resulted in the time-dependent excretion-secretion of radiolabelled parasite macromolecules (ES). Molecules labelled with amino acids ([35S] methionine, [3H] leucine) covered a wide range of molecular weights, whereas labelling with [3H] glucosamine produced predominantly molecules of high molecular weight. Many of the products were recognized by antibodies in two serum pools from humans infected with Onchocerca volvulus. O. gibsoni ES may therefore provide a substitute source of material for studies on the ES of the less readily available human parasite.

Animals↗
PubMed1979

Onchocerciasis transmission potentials of four species of Guatemalan simuliidae.

Two complete days of collections and dissections of all black fly species landing on two persons infected with Onchocerca volvulus were made at monthly intervals for 13 months within a single endemic area of Guatemala. A comparison of the infective biting densities and transmission potentials showed that Simulium ochraceum was the only significant vector.

Adult↗
PubMed1990

Onchocerciasis in Benue State of Nigeria. VI. The prevalence and distribution of the disease among the human population in Sati-Ikyov village.

Following our report on onchocherciasis among the Ikyov and Nanev clans, we initiated a survey of the prevalence and distribution on onchocerciasis in some villages in Benue State, Nigeria. Out of the 1,558 inhabitants (619 males and 608 females) examined, 1,227 (78.8%) were found to carry microfilariae (mf) of Onchocerca volvulus (mean density: about 20/skin snip). The presence and number of mf from the right and left iliac crests were comparable. The findings indicate that clinical manifestations in onchocerciasis remain vital indices for rapid prospection.

Animals↗
PubMed1994

The chemotherapy of onchocerciasis XVII. A clinical evaluation of albendazole in patients with onchocerciasis; effects of food and pretreatment with ivermectin on drug response and pharmacokinetics.

Three pharmacokinetic studies were conducted in Ghanaian patients in support of investigations of albendazole and its combination with ivermectin in the treatment of onchocerciasis. These included dose-finding studies, investigations into the influence of a fatty meal on the relative bioavailability of albendazole as assessed by the measurement of concentrations of albendazole sulphoxide and the effect of prior treatment with ivermectin on antiparasitic efficacy and plasma concentrations of albendazole suphoxide. Increasing the dose of albendazole from 800 mg x 3 daily to 1200 mg x 3 daily produced no additional antiparasitic effects although plasma concentrations of albendazole sulphoxide were increased in proportion to dose size. Moreover, the plasma concentration vs time profiles suggest that most of the effects observed may have been due to the first 800 mg dose. Administration of ivermectin had no effect on the pharmacokinetics of albendazole sulphoxide and there was no additive effect on the parasite. Albendazole was well tolerated and its administration 5-7 days after ivermectin produced little additional reaction. Although it is not macrofilaricidal, it does possess important chemosterilant properties which are enhanced by its administration with a fatty breakfast. Under these conditions, the relative bioavailability of albendazole is increased four-fold. These studies support further work with albendazole administered with food either as a single dose, as multiple single doses repeated at intervals of several months and its coadministration with ivermectin. They also encourage the belief that a more potent and bioavailable benzimidazole may be macrofilaricidal or a permanent chemosterilant for Onchocerca volvulus on single dosage.

Adolescent↗
PubMed1987

Primate model for onchocerciasis research.

A major impediment to progress in research in onchocerciasis has been the lack of a suitable animal model. However, chimpanzees can be reliably infected by injection of living third-stage larvae of Onchocerca volvulus, and develop a pattern of infection that closely resembles that seen in humans. This includes the formation of nodules by adult worms, the subcutaneous distribution of microfilariae and the apparent lack of development of resistance to infection after repeated larval challenge. Ocular lesions resembling those in humans have not been observed in animals studied so far, but this may reflect in part the low intensity of infection and the limited time of observation. We infected 18 chimpanzees by subcutaneous injection of 250 third-stage larvae of O. volvulus. Six received ivermectin on day 1, another six received ivermectin on day 28 after infection, and six received no drug. Four control animals received no infective larvae and no drug. During the first year after infection, all three infected groups, but not control animals, have shown a clear increase in their lymphocyte blastogenic response to crude O. volvulus antigen in vitro. Antibody responses have also been increasing with time. Further assessment of the cellular and antibody responses in the infected chimpanzees is under way, as is evaluation of the effects of ivermectin on the course of infection.

Animals↗
PubMed1997

Vector-parasite transmission complexes for onchocerciasis in West Africa.

BACKGROUND: In West Africa, there are two strains of the filarial parasite Onchocerca volvulus, which differ in their ability to induce ocular disease. Transmission studies have suggested that six sibling species of the parasite vector, the black fly Simulium damnosum sensu lato, allow development of the two strains of O volvulus with varying efficiency. We aimed to test the hypothesis of parasite-vector complexes, whereby the two parasite strains, known as forest and savanna, are preferentially transmitted by distinct groups of the species of S damnosum S l. METHODS: During 1993 and 1994, wild black flies were collected from 11 river basins within the area covered by the Onchocerciasis Control Programme (OCP). The flies were dissected and filarial larvae, ovaries, and malpighian tubules removed. Genomic DNA was extracted from larvae, and PCR amplification was used to classify O volvulus parasites as forest or savanna strains. PCR-amplified DNA from ovaries and malpighian tubules was used to distinguish sibling species of S damnosum s l. S yahense and S squamosum were distinguished by body colour. FINDINGS: 214 of 105105 flies dissected were infected with filarial larvae; 84 of these were infected with mature O volvulus parasites. Of the 35 savanna-dwelling infected flies. 17 carried forest-strain parasites and 18 savanna-strain parasites. Of the 45 infected flies identified as the forest dwelling sibling species. 20 carried savanna-strain parasites and 25 forest-strain parasites. No significant differences were found in the numbers of mature larvae of each strain carried by the forest-dwelling species of fly or in the number of forest and savanna larvae in savanna-dwelling vector species. INTERPRETATION: Vector-parasite transmission complexes do not currently play a part in the biology of O volvulus transmission in the area of the OCP in West Africa. This finding has important strategic implications for the future of efforts to control onchocerciasis in West Africa.

Africa, Western↗
PubMed1998

Detection of the filarial parasite Mansonella streptocerca in skin biopsies by a nested polymerase chain reaction-based assay.

To differentiate the skin-dwelling filariae Mansonella streptocerca and Onchocerca volvulus, a nested polymerase chain reaction (PCR) assay was developed from small amounts of parasite material present in skin biopsies. One nonspecific and one specific pair of primers were used to amplify the 5S rDNA spacer region of M. streptocerca. Biopsies with different microfilaria densities obtained from 104 Ugandans living in an area endemic for M. streptocerca were tested using both the nested PCR assay and standard parasitologic assessment of microfilariae. All 82 samples from microfilaria carriers were positive when tested using the nested PCR assay. In addition, M. streptocerca DNA could be detected in 16 samples thought to be microfilaria negative. Furthermore, six days following ivermectin treatment, M. streptocerca DNA was found in 12 of 14 microfilaria-negative biopsies. Control skin samples from patients infected with O. volvulus were all negative in the nested PCR assay. This assay improves the diagnosis of M. streptocerca and will facilitate further epidemiologic studies.

Animals↗
PubMed1979

Some observations on onchocerciasis including sowda in the Yemen Arab Republic.

A pilot study on onchocerciasis and sowda was carried out in the south-western region of the Yemen Arab Republic. Of 61 persons examined in eight villages 35 (= 57%) were found positive for microfilariae by the skin-snip method, 13 had typical manifestations of sowda, 17 had other onchocercal-suggestive skin lesions and five had subcutaneous nodules. A single larva of Simulium damnosum s.I. was collected in Wadi Barakani. Numerous larvae and pupae of S. ruficorne and S. hargreavesi were taken in fast-flowing streams in four localities. The examination of microfilariae and adult worms by scanning electron microscopy as well as the histochemical staining of microfilariae for the demonstration of acid phosphatase activity confirmed that the concerned filaria belongs to the species Onchocerca volvulus. No morphological differences could be detected between the smaller number of the examined worms from the Yemen and the extensive parasite material from Liberia, West Africa.

Adolescent↗
PubMed1987

Clinical responses in human onchocerciasis: parasitological and immunological implications.

Onchocerciasis can cause severe dermal and ocular disease due, it is thought, to the events surrounding the destruction of the microfilarial stage. The evolution of papular pruritic dermatitis and punctate keratitis is clearly related to the killing of microfilariae. Other more chronic changes such as dermal and epidermal atrophy are probably due to repeated episodes of microfilarial killing. It is common to find that not all patients are, at any one time, mounting clinically obvious destructive host responses against the microfilariae, and such individuals can carry very high loads of parasites without any apparent adverse effects. The immunological basis of the differences between these types of patients forms one of the most important questions in the pathogenesis of onchocerciasis today. Various explanations are now emerging. These include immunosuppressive factors and variation in the form of Onchocerca volvulus antigens presented to the host. Clinical presentations of this disease appear to reflect variations in host responses and can be used to provide information concerning the protective immune responses an individual can mount against this parasite.

Animals↗
PubMed1992

Eye lesions, blindness and visual impairment in the Taraba river valley, Nigeria and their relation to onchocercal microfilariae in skin.

2876 persons in fourteen communities in the Taraba River Valley, Nigeria were examined for eye lesions and tested for visual acuity using the 'tumbling E'. The individuals were also examined for microfilaria of Onchocerca volvulus. More than one-tenth of the population were blind, while another 16.1% had visual impairment. The prevalence of blindness was in excess of 20% in six communities, with one community recording 71.9% blindness rate. All forms of visual involvement increased with age but were similar between sexes. Eye lesions were related to the level of vision. Both eye lesions and vision deteriorate with increase in age. Vision seems to worsen with increase in prevalence and intensity of O. volvulus. Large microfilarial loads were associated with severe eye damage and blindness. These findings indicate that the Taraba river valley could be one of West Africa's worst foci of onchocercal blindness.

Adolescent↗
PubMed1992

[Effect of a sublethal dose of an insect growth regulator on the physiology of onchocercosis vectors].

In most of the large scale vector control programs, the larviciding operations are not fully successful, resulting in a surviving vector population due to the use of sublethal doses. This problem leads the authors to study the effect of such doses upon the future of the residual population in order to know if it represents an epidemiologically dangerous population. One insect growth regulator was selected to study this phenomenon using Onchocerca volvulus as the parasite and Simulium damnosum s.l. as the vector. The experiment was conducted under field conditions by treating a river of a savanna area in north Cameroon where onchocerciasis remains endemic. The sublethal doses yielding 20% in adult blackflies from treated larvae was determined and the effects on physiological and vectorial capacities were assessed. The authors also carried out observations on the peritrophic membrane formation and the passage of microfilariae into the hemocele. The observation of flies fed on Onchocerca after larval treatment showed that this insecticide had a light effect on female longevity but did not induce any modifications in the life cycle of the parasite. An unusual high proportion of infected females, observed by the authors, is probably due to an anomaly in the phenomenon of limitation. However, the histological analysis showed to the evidence that no apparent difference between treated and untreated blackflies was observed although the process of blood meal digestion seemed slightly altered in treated flies.

Animals↗
PubMed1991

2-acetylpyridine thiosemicarbazones. 13. Derivatives with antifilarial activity.

Several members of a series of 2-acetylpyridine thiosemicarbazones possess in vivo and in vitro macrofilaricidal properties. The most promising of the group tested is N4-(2-aminophenyl)-2-[1-(2-pyridinyl)ethylidene]-hydrazinecarbothioam ide (4), which suppressed 100% of the macrofilariae of Brugia pahangi and 94% of those of Acanthocheilonema viteae in the jird at a dose of 25 mg/kg per day x 5. Compounds 4 and 14 were also shown to inactivate or kill Onchocerca gutturosa and Onchocerca volvulus adult worms as measured by the loss of their motility or the inhibition of the conversion by the worms of the dye MTT to formazan.

Animals↗
PubMed1990

Antibodies against the cuticlin of Ascaris suum cross-react with epicuticular structures of filarial parasites.

The insoluble cuticlin from the cortical zone of the cuticle of adult Ascaris suum was purified and used to raise antibodies in C57/bl mice. The specificity of the antibodies for the external cortical layer was shown in the indirect immunofluorescence antibody test and by immunoelectronmicroscopy. A very high specificity for the external cortical layer was found. Some cross-reactions with cuticular collagens occurred, and increased after booster immunizations. The anti-cuticlin antibody cross-reacted with the electron-dense layers of the cortical zones of adult Acanthocheilonema viteae and Brugia pahangi. A very weak reaction was found in the cortical zone of adult Onchocerca volvulus. In the cuticles of third stage larvae of all three species mainly epitopes in the cortical zones were labelled. In no case did the anti-cuticlin antibody interact with the outermost surface of the cuticle.

Animals↗
PubMed1986

A study on antigen recognition by onchocerciasis patients with different clinical forms of disease.

Sera from 40 onchocerciasis patients from the Yemen Arab Republic with either mild localized forms of onchocerciasis, intermediate or severe localized forms of the disease or generalized forms of infection were studied with respect to their IgG and IgM response against Onchocerca volvulus antigens. Immunoblotting, performed with SDS-PAGE-separated proteins of female O. volvulus and quantified by densitometric scanning, revealed IgG and IgM antibodies against worm components in sera of all patients. Persons with intermediate or severe localized forms of onchocerciasis had a stronger IgG response against more proteins than individuals of the other groups. However, some antigens (Mr 21, 23, 30, 33 kDa) induced comparable quantities of IgG in all groups. The IgM response of patients with mild localized forms of onchocerciasis was more intensive and directed against more antigens than in the other groups. No antigens were detected that were recognized only by individuals with low levels of microfilaridermia. In all groups, varying concentrations of antibodies against cuticle, muscle/hypodermis layer and/or uterus of female O. volvulus were detected by the indirect immunofluorescence test using frozen worm sections as antigen. The highest mean antibody titres were found in patients with intermediate and severe localized forms of disease.

Adult↗