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PubMed2001

Integrin-like RGD-dependent cell adhesion mechanism is involved in the rapid killing of Onchocerca microfilariae during early infection of Simulium damnosum s.l.

Injection trials with compatible and non-compatible Onchocerca species into S. damnosum s.l., the vector of human and bovine onchocerciasis, demonstrated that the rapid killing of microfilariae within the blackfly's haemocoel is species specific. In the presence of the peptide RGDS as a blocking agent for integrin-like receptors of haemocytes, the survival of O. ochengi microfilariae in its natural intermediate host was significantly increased. This increased survival 24 h p.i. correlated with a significant decrease of apoptosis levels in the microfilariae following a 2 h exposure to the haemolymph in vivo. These findings suggest that haemocytes are directly involved in the killing of Onchocerca microfilariae in the blackfly.

Animals↗
PubMed1998

Onchocerca ochengi: assessment of the Simulium vectors in north Cameroon.

In the savanna areas of tropical Africa, cattle are frequently infected with the filaria Onchocerca ochengi. This parasite is closely related to Onchocerca volvulus, the causative agent of human onchocerciasis (river blindness), and is capable of developing in the same vector, Simulium damnosum s.l. In North Cameroon, where both O. ochengi and O. volvulus are endemic, we carried out a field study (reported in this and 2 following papers) to examine to which extent the transmission of the 2 parasite species overlap and what influence this has on the epidemiology of human onchocerciasis. In this paper we report our experiments to determine which of the S. damnosum species in North Cameroon act as vectors of O. ochengi, how efficiently they do so and whether other Simulium species play a vector role. To this end, infected cattle were exposed near 5 rivers in different geographical areas. Among 14 Simulium species identified as aquatic and/or adult stages at these rivers, only 6 (S. squamosum, S. damnosum s.s., S. sirbanum, S. bovis, S. wellmanni and S. hargreavesi) were found to bite cattle in important numbers in at least 1 of the sites. The 3 species of the S. damnosum complex were all capable of ingesting microfilariae (mf) of O. ochengi and developing a proportion of them to infective larvae (L3). Whereas S. squamosum and S. damnosum s.s., the prevailing vectors in the Guinea and Sudan savanna respectively, showed a high vector competence (17% of ingested mf developed to L3), S. sirbanum, which was much rarer in both areas, appeared to have a much lower susceptibility (2%). Other boophilic Simulium species were only seen in certain sites and seasons, being either incapable of ingesting important numbers of O. ochengi mf from body regions where these mf were abundant (S. bovis, S. hargreavesi); not able to support the development of ingested mf to L3 (S. wellmanni), or bit cattle preferentially in the ears, where O. ochengi mf do not occur (S. hargreavesi). We conclude that in North Cameroon members of the S. damnosum complex are the only important vectors of O. ochengi, with S. squamosum and S. damnosum s.s. being the main vectors.

Animals↗
PubMed2000

Onchocerca-Simulium complexes in Venezuela: can human onchocerciasis spread outside its present endemic areas?

The compatibility between sympatric and allopatric combinations of Onchocerca volvulus-anthropophilic species of Simulium was studied in the north-eastern focus of human onchocerciasis as well as in a densely populated locality of the Amazonas State in Venezuela. The objectives were to test the conjecture that local adaptation exists between the parasite and its vectors (the Onchocerca-Simulium complex hypothesis), and assess the possibility of the infection spreading from its present distributional range. For the homologous combination, O. volvulus-S. metallicum cytospecies E in Anzoátegui State (north-eastern focus), parasite yield was 45% in contrast to 1% for the heterologous, southern parasite-S. metallicum infection. This was significantly lower than the parasite yield (4-10%) expected after allowing for the effect of density-dependent limitation of infective larval output described in this paper for S. metallicum. The population of S. exiguum s.l. from southern Venezuela allowed no larval development beyond the L1 stage of either northern or southern parasites. Mechanisms for such refractoriness probably operate at the level of the thoracic muscles, not affecting microfilarial uptake or migration out of the bloodmeal. The parasite yield of southern O. volvulus in S. oyapockense s.l. flies biting man at Puerto Ayacucho (Amazonas) was about 1%, in agreement with the figures recorded for highly compatible sympatric combinations such as O. volvulus-S. ochraceum s.l. in Guatemala. No infective larval development of the northern parasite was observed in southern S. oyapockense. These results, together with considerations of typical worm burdens in the human host, presence/absence of armed cibaria in the simuliids, parasite-induced vector mortality, and fly biting rates, suggest a lower potential for onchocerciasis to spread between the northern and southern endemic areas of Venezuela than that between Amazonian hyperendemic locations and settlements outside this focus with high densities of S. oyapockense s.l.

Adult↗
PubMed2000

Onchocerca ochengi infections in cattle as a model for human onchocerciasis: recent developments.

The bovine parasite Onchocerca ochengi is a nodule-dwelling filarial nematode, closely related to O. volvulus, the causal agent of human River Blindness, and, sharing with it, the same vector. This brief review, based on a presentation at the BSP Autumn Symposium 1999, describes recent work supported by the WHO Drug Development Research Macrofil programme and the Edna McConnell Clark Foundation vaccine development programme, to research the chemotherapy and immunology of onchocerciasis utilising this model system, with experimental infections in Liverpool and field infections in northern Cameroon. In a series of chemotherapeutic trials involving 10 compounds in 20 treatment regimes, the comparability of drug efficacy against O. ochengi with that described against O. volvulus has been demonstrated. Repeated, long-term treatment with oxytetracycline has been shown to be macrofilaricidal and the effect is hypothesized to be related to action on Wolbachia endobacteria, abundant in O. ochengi. Avermectins/milbemycins are not macrofilaricidal (even in high and repeated long-term treatments) but induce sustained abrogation of embryogenesis. In prospective, field exposure experiments with naive calves, prophylactic treatments with ivermectin and moxidectin prevented the development of adult worm infection, raising the possibility that drug-attenuated larval challenge infections may induce immunity. Putatively immune adult cattle exist in endemically exposed populations, and these have been shown to be significantly less susceptible to challenge than age-matched naive controls, whereas radically drug-cured, previously patently-infected cattle were not. Experimental infections with O. ochengi have revealed the kinetics of the immune response in relation to parasite development and demonstrate analogous responses to those reported in O. volvulus infection in humans and chimpanzees. In an immunization experiment with irradiated L3 larvae, cattle were significantly protected against experimental challenge--the first such demonstration of the experimental induction of immunity in a natural Onchocerca host-parasite system. Taken collectively, these studies not only demonstrate the similarity between the host-parasite relationships of O. ochengi in cattle and O. volvulus in humans, but promise to advance options for the control of human onchocerciasis.

Animals↗
PubMedDate not supplied

A DNA sequence specific for forest form Onchocerca volvulus.

Onchocerciasis, or river blindness, is caused by infection with Onchocerca volvulus, a filarial parasite which infects about 40 million people in Africa and Latin America. Epidemiological, clinical, entomological and serological studies of African onchocerciasis led to the hypothesis that Onchocerca volvulus exists in different forms in the forest and savannah. It is uncertain if these differences are due to genetic differences within O. volvulus itself, or to epigenetic factors, such as differences in the host populations. To date no basic biochemical differences between the forest and savannah populations of O. volvulus has been found, although isoenzyme studies have shown that differences in allele frequency between forest and savannah populations exist. Here we describe the isolation of a DNA sequence that seems to be specific for the forest form of O. volvulus, the first indication of a basic genetic difference between the savannah and forest forms.

Base Sequence↗
PubMed2003

Cutaneous pathology in onchocerciasis associated with pronounced systemic T-helper 2-type responses to Onchocerca volvulus.

BACKGROUND: Of 18 million people world-wide who are infested with the tissue nematode Onchocerca volvulus, more than 30% are considered to have skin lesions, the pathomechanisms of which are poorly understood. OBJECTIVES: To relate skin changes associated with onchocerciasis to parasitological findings and systemic cellular immune responses. METHODS: In the course of a genetic study, 691 members of 241 families exposed to hyperendemic O. volvulus transmission and free of other filarial or schistosomal infestations were studied clinically, by counting palpable Onchocerca nodules and skin microfilariae, by measuring peripheral blood cell (PBC) counts and total serum IgE, and by determining PBC in vitro proliferation and cytokine secretion in response to O. volvulus antigen. RESULTS: Of 691 individuals studied, 219 presented with onchocerciasis-associated skin changes. The groups of individuals with and without skin lesions neither differed in prevalences nor in average numbers of microfilariae. Compared with individuals without skin lesions, pronounced systemic T-helper (Th) 2-type responses were found with a trend of increasing intensity in the order of depigmentation, papular dermatitis, atrophy and lichenified dermatitis. Differences between the groups were most pronounced for serum IgE, less so for eosinophilia, and relatively weak for PBC proliferation and interleukin-5 secretion. CONCLUSIONS: Skin lesions in onchocerciasis are associated with a spectrum of increasing generalized Th2-type responses ranging from low reactivities in cases of depigmentation alone to strong reactivities in cases of lichenification.

Adolescent↗
PubMed1999

Prenatal immune priming in onchocerciasis-onchocerca volvulus-specific cellular responsiveness and cytokine production in newborns from infected mothers.

This study investigated the effect of maternal Onchocerca volvulus infection on humoral and cellular responsiveness in newborn children and their mothers. Onchocerca volvulus-specific IgG isotypes and IgE were significantly elevated in infected mothers and their infants. One year post partum, O. volvulus-specific IgG4 was strongly reduced in children of infected mothers, while IgG1 responses weakened only slightly. Umbilical cord mononuclear blood cells (UCBC) and peripheral blood cells (PBMC) from mothers proliferated in response to phytohaemagglutinin (PHA), concanavalin A (Con A), and the bacterial antigens streptolysin-O (SL-O) or purified protein derivative (PPD). UCBC from neonates born to O. volvulus-infected mothers responded lower (P < 0.01) to Con A (at 5 micrograms/ml), PPD (at 10 and 50 micrograms/ml) and O. volvulus-derived antigens (OvAg) (at 35 micrograms/ml), and in parallel, a diminished cellular reactivity (P < 0.01) by PBMC was observed to OvAg in mothers positive for O. volvulus. Several Th1-type (IL-2, IL-12, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha)) and Th2-type (IL-4, IL-5, IL-10, IL-13) cytokines were secreted by UCBC and PBMC in response to OvAg, bacterial SL-O and PHA. OvAg did not stimulate IL-2 and none of the mitogens or antigens induced production of IL-4 in neonates. In response to OvAg, substantially elevated (P < 0.01) amounts of IFN-gamma were produced by UCBC from newborns of O. volvulus-infected mothers. UCBC secreted low levels of IL-5 and IL-13, while higher amounts of IL-10 were found (P < 0. 01) in newborns from onchocerciasis-free mothers. In conclusion, maternal O. volvulus-infection will sensitize in utero parasite-specific cellular immune responsiveness in neonates and activate OvAg-specific production of several Th1- and Th2-type cytokines.

Adolescent↗
PubMed1997

The diverse expression of immunity in humans at distinct states of Onchocerca volvulus infection.

This study examined the development and persistence of immunity in humans presenting defined states of Onchocerca volvulus infection, i.e. in exposed endemic control individuals without microfilaridermia and clinical disease, in patients with patent or post-patent onchocerciasis, and in patients concurrently infected with Mansonella perstans. Onchocerca volvulus antigen (OvAg)-specific cellular reactivity was significantly diminished in microfilariae (mf)-positive patients, while the highest reactivity was measured in exposed but mf-negative endemic controls, those being free of any clinical signs of onchocercal disease. In patients who became post-patent, responses to OvAg were significantly augmented, but did not approach entirely the magnitude observed in endemic controls. In onchocerciasis patients with concurrent mansonelliasis, cellular unresponsiveness to OvAg persisted, even when mf of O. volvulus were eliminated permanently by repeated ivermectin therapy. Cells from mf-positive onchocerciasis patients produced significantly less interferon-gamma (IFN-gamma) (P < 0.01) and interleukin-5 (IL-5) (P < 0.05) in response to OvAg than those taken from endemic controls or post-patent individuals in whom IFN-gamma and IL-5 production was similarly high. In contrast, both OvAg-driven as well as spontaneous IL-10 secretion was higher in mf-positive patients than in endemic controls or post-patent cases. In all individuals examined, serological recognition of OvAg by immunoglobulins was dominated by IgG4; in mf-positive patients OvAg of 205,000-12,000 molecular weight (MW) were strongly bound. In post-patent individuals, and similarly in endemic controls. OvAg recognition by IgG4 varied from intense (with numerous antigens being recognized) to weak or absent antigen binding. Significantly elevated OvAg-specific IgG isotypes were measured in mf-positive onchocerciasis patients in comparison with endemic controls or post-patent individuals (with the exception of IgG3). IgG1, IgG2 and IgE were higher, but IgG4 was lower in endemic controls compared with post-patent onchocerciasis patients. The ratios of IgG4/IgG1 differed (P < 0.001) between endemic controls and mf-positive or post-patent onchocerciasis patients, with IgG4/IgG1 ratios of R < 3.0 being characteristic for endemic controls and post-patent O. volvulus infection. In conclusion, this cross-sectional immunoepidemiological investigation showed that distinct states of O. volvulus infection correlate with a particular cellular and humoral immune response. The mf-free condition appeared to be associated with a vigorous parasite-specific cellular reactivity and a particular cytokine production profile, while concurrent M. perstans infection depressed OvAg-specific cellular responsiveness. Antibody responses, in all likelihood, reflected the intensity and state of infection, and not the degree of acquired immunity protective against parasite aggregation.

Adolescent↗
PubMed1999

IL-5 dominates cytokine responses during expression of protective immunity to Onchocerca lienalis microfilariae in mice.

In a model of protective immunity against Onchocerca microfilariae (mf), it has been demonstrated previously that immunocompetent mice clear a primary infection and are highly resistant to re-infection. This immunity correlates with CD4+ Th2 cells, is dependent on IL-5 but not IL-4, and can be transferred adoptively with spleen cells. In the current investigation, high levels of spontaneous proliferation and of IFN gamma production were observed in splenocyte cultures from immune mice, compared with cells from naive controls. Antigen-specific proliferation also occurred in immune cells, being vigorous following stimulation with adult worm antigen, but not with antigens from developing embryos or mf. Levels of IL-4, IL-5 and IFN gamma induced by the various antigens was similar, indicating that activation of alternate T helper cell sub-sets was unlikely to explain the lack of cellular responsiveness. After a primary inoculation with mf, spleen cells from infected mice co-produced IFN gamma and IL-5. In contrast, IFN gamma production was downregulated while IL-5 levels remained high during active elimination of a challenge infection. Significant levels of IL-4 production occurred only once parasite clearance had begun. These data confirm the importance of IL-5 in protection against Onchocerca mf in mice and question the role of IFN gamma in the expression of immunity. Production of high levels of IL-5 correlated with blood and tissue eosinophil mobilization during the clearance of a challenge infection.

Animals↗
PubMed2003

Regulatory effects of IL-12 and IL-18 on Onchocerca volvulus- and Entamoeba histolytica-specific cellular reactivity and cytokine profiles.

In the present study, the cytokines interleukin (IL)-12 and IL-18 were evaluated for their capacity to modulate and to re-direct in vitro parasite antigen-specific cellular responsiveness in patients exposed to Onchocerca volvulus and Entamoeba histolytica infection. We found that IL-18 was highly capable of reducing parasite antigen-induced IL-10 production by PBMC. In contrast, addition or neutralization of IL-12, also in combination with IL-18 and the interferon-gamma-inducible chemokine IP-10 did not affect IL-10 production. Interestingly, the highest IL-10 levels were measured when IL-18 and IP-10 were both neutralized. Although having no effect on IL-10, IL-12 strongly promoted spontaneous and parasite antigen-driven IFN-gamma production by PBMC, whereas IL-18 was only moderately affecting IFN-gamma release by PBMC re-stimulated with E. histolytica- or O. volvulus-specific antigens. Both IL-12 and IL-18 diminished the cellular production of IL-13, and a synergistic effect was observed when the cytokines were combined. Likewise, neutralization of IL-12 enhanced Entamoeba and Onchocerca antigen-driven IL-13 production, but no further increase of IL-13 was observed, when anti-IL-12 and anti-IL-18 were used together. This study disclosed that IL-18 will significantly down-regulate parasite-specific IL-10 production, whereas IL-12 induced IFN-gamma and inhibited IL-13 production by PBMC from humans exposed to O. volvulus and E. histolytica. Such selective immune-regulatory capacity of IL-12 and IL-18 may comprise an important tool to re-direct polarized cytokine responses towards a balanced Th1/Th2 cytokine profile, which may prevent pathology and promote immunity against helminth and protozoan parasite infections.

Adolescent↗
PubMed1996

Vaccination generates serum-mediated protection against Onchocerca lienalis microfilariae in the mouse.

Mice vaccinated with an aqueous extract of Onchocerca lienalis microfilariae (mf) plus adjuvant exhibited 51% protection against challenge with live mf. Protection was ablated by prior treatment of the extract with heat or proteinase K, indicating the involvement of proteinaceous epitope(s). A 54% level of protection was conferred on naive mice by passive transfer of serum from vaccinated donors, suggesting that host resistance was principally mediated by humoral components of the immune response. In contrast, the protection induced by sensitization of mice with living mf is transferable with cells, but not serum. Western blot data reveal different antigen recognition profiles for serum antibodies from these two groups of mice. These results indicate that vaccination and infection activate distinct protective mechanisms against Onchocerca mf in the mouse.

Animals↗
PubMed1996

Polymerase chain reaction for detecting Onchocerca volvulus in pools of blackflies.

The detection of Onchocerca volvulus infected simuliids or blackflies is routinely done by dissection and microscopic examination of individual flies, but this method is tedious and time consuming. Here we describe a method of detecting single O. volvulus infected blackflies in pools of uninfected blackflies. Using a PCR with Onchocerca specific primers it is possible to reproducibly detect one heavily infected blackfly in a pool of 80 flies, or to detect one blackfly inoculated with one microfilaria in a pool of 20 flies. With the method described large numbers of blackflies can be rapidly screened for the presence of O. volvulus infected flies.

Animals↗
PubMed2002

Subconjunctival filariasis due to Onchocerca sp. in dogs: report of 23 cases in Greece.

In the present study, we describe a series of 23 cases of ocular subconjunctival parasitic granulomas in dogs, admitted to the Clinic of Surgery, Faculty of Veterinary Medicine of the Aristotle University of Thessaloniki, Greece, between 1997 and 2000. The ophthalmic manifestations in all animals were periorbital swelling, discomfort, photophobia, conjunctival congestion, and discharge. A more detailed examination revealed the presence of periocular masses (nodules) on the subconjunctival bulbar space. Granulomatous or cyst-like formations were extracted surgically, and were found to contain thread-like nematode parasites. A histologic and parasitologic examination of tissues and parasites was carried out. Diagnosis of parasitic granulomas was made and the parasite was identified as Onchocerca sp. This is the largest series of cases reported of aberrant Onchocerca infections in dogs coming from one geographic location.

Animals↗
PubMedDate not supplied

[Description of Onchocerca dewittei n. sp. (Filarioidea), parasite of Sus scrofa, in Malaysia (author's transl)].

Onchocerca dewittei n. sp. was collected from a wild Boar at the metatarse level (tendons and subcutaneous connective tissue); it can be differentiated from other species by the female cuticle showing straight ridges which overlap in the lateral fields, and by its relatively thick microfilaria (length 228-247 mu and width 6-7 mu). This suidean Onchocerca displays some primitive characters such as straight ridges and persistency of ten pairs of caudal papillae in the male; but as a whole this species is undoubtedly more highly evolved than O. raillieti Bain, Müller and coll., 1976, a parasite of Equidae.

Animal Population Groups↗
PubMedDate not supplied

[Occurence of Onchocerca tarsicola Bain and Schulz-Key, 1974, in reindeer (author's transl)].

Onchocerca tarsicola is recorded from reindeer (Rangifer tarandus L.). This parasite is originally described from red deer (Cervus elaphus L.). There are indications that reindeer may not be the primary host of O. tarsicola: 1. Reindeer is parasitized only by O, tarsicola whereas red deer, due to speciations, is carrying three related Onchocerca species from the same line. 2. O. tarsicola, usually found along tendons distal of the tarsal and carpal joints, is in reindeer frequently found at aberrant locations which is commonly observed in connection with "transfuga" parasites. 3. Heavy infestations of O. tarsicola in reindeer seem to have started in the late sixties and since then have become more and more extensive.

Animals↗
PubMed1991

Uptake of chloroquine by Onchocerca volvulus in vivo and in vitro.

Patients infected with Onchocerca volvulus in the Cayapa River focus in north-east Ecuador were given 500 mg chloroquine diphosphate (CQ) orally prior to nodulectomy. The concentrations of CQ were determined in parasite fragments and host tissue dissected from the nodules, in skin overlying the nodules, and in plasma at 3, 4, 7, and 24 hours after dosing. Onchocerca volvulus took up CQ rapidly, in some cases accumulating the drug to concentrations of over 600 pmol mg-1 worm tissue by three hours, and maintaining similar concentrations through 24 hours. These amounts were markedly higher than peak concentrations in plasma (3.16 pmol microliters-1) and in host tissues (78 pmol mgm-1) and skin (up to 93 pmol mg-1). In vitro uptake of CQ by females of O. volvulus was greater under alkaline conditions (pH 8.4) than at pH 6.8 and 7.4. Uptake reached equilibrium after one to two hours, with final concentrations being approximately 10 times lower than those reached in vivo. Inhibitory effects of chloroquine and its major metabolite desethylchloroquine on the motility of O. volvulus and other filariae have been observed previously in vitro; whether or not the drug had adverse effects on adult parasites in vivo was not determined in these experiments. However, the results illustrate the accessibility of O. volvulus to blood borne agents in vivo, and the potential importance of pharmacodynamic characteristics in the search for new macrofilaricidal agents.

Animals↗
PubMed2006

Antifilarial activity in vitro of polycarpol and 3-O-acetyl aleuritolic acid from cameroonian medicinal plants against Onchocerca gutturosa.

Previous results have revealed the antifilarial activities of crude extracts and pure compounds from some Cameroonian medicinal plants against Onchocerca volvulus and Onchocerca gutturosa. In our efforts to find new filaricidal agents against adult male O. gutturosa worms, we have isolated and screened three compounds: polycarpol and polyveoline from Polyalthia suaveolens (Annonaceae) and 3-O-acetyl aleuritolic acid from Discoglypremna caloneura (Euphorbiaceae). Only polycarpol and 3-O-acetyl aleuritolic acid exhibited significant inhibitory activities on the vitality of adult male worms of O. gutturosa using Amocarzine as positive control compound. The motility reduction values were 28.6 and 57.1%, and the inhibition of MTT reduction values 80.0 and 64.8% respectively.

Animals↗
PubMed1988

Characterization of an immunodominant Onchocerca volvulus antigen with patient sera and a monoclonal antibody.

Adult Onchocerca voluvlus and infective larvae, but not microfilariae contain an immunodominant antigen (33,000 and 21,000 Mr in females, 39,000, 33,000, and 21,000 Mr in males, 133,000 Mr in infective larvae) which is recognized by an Onchocerca-specific mAb. The component is part of the reproductive organs and muscles. 96.2% of onchocerciasis sera contained antibodies detectable by immunoblotting against it. Antigen purified by immunoaffinity chromatography was specifically recognized in immunoblots by onchocerciasis sera, but not by sera from other filarial infections. The high immunogenicity, the specificity, and the occurrence in infective larvae of this antigen indicate an immunodiagnostic potential and a possible role in the immunobiology of the parasite.

Animals↗