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PubMed1994

HLA-D alleles associated with generalized disease, localized disease, and putative immunity in Onchocerca volvulus infection.

Human infections with the tissue nematode Onchocerca volvulus result in a variety of clinical conditions that possibly include protective immunity. In a West African area hyperendemic for human onchocerciasis, 120 residents were classified according to clinical and laboratory findings as presenting with generalized onchocerciasis, localized onchocerciasis, or as being putatively immune. The three groups differed in the distribution of HLA-D variants as determined by DNA typing. The most pronounced differences were found among alleles of the DQ loci. The haplotype DQA1*0501-DQB1*0301 was significantly more frequent among putatively immune individuals than among patients with generalized or localized disease. Conversely, DQA1*0101-DQB1*0501 and, independently, the allele DQB1*0201 were more frequent in generalized disease than in localized disease or putative immunity. In these correlations, the frequencies of allelic variants were in localized disease intermediate to those of the two other groups. The only distinct association found with localized disease was that of the DP allele DPB1*0402. The findings indicate that HLA-D variants influence the course of O. volvulus infection and help to define a state that may reflect protective immunity.

Adolescent↗

PubMed1997

Antigenicity and specificity of very low molecular weight Onchocerca volvulus polypeptides in the range 2.2-12.5 kD.

Onchocerca volvulus polypeptides in the molecular mass range of 2.2 to 12.5 kD were separated by Tricine-SDS-PAGE and the serological recognition of these very low molecular weight antigens (VLMW-OvAg) was then investigated by immuno-blotting. Sera from 21 onchocerciasis patients as well as from 53 individuals with other filariases were used to determine the sensitivity and specificity of detection of individual VLMW-OvAg. In onchocerciasis patients, up to 16 VLMW-OvAg were recognized predominantly by IgG1 and IgG4, while only few antigens were recognized by IgG2 and IgG3. The antigen recognition pattern varied individually, but 4 VLMW-OvAg of 8.6, 6.2, 5.4, and 5.1 kD, respectively, were bound by IgG4 from more than 90% of the onchocerciasis patients. Six VLMW-OvAg of 7.3, 5.8, 5.4, 4.0, 3.8, and 3.6 kD were recognized exclusively by IgG1 from onchocerciasis patients. In amicrofilaraemic filariasis patients with lymphatic pathology, a strong reactivity of IgG3 to an OvAg of 2.2 kD was observed, indicating a possible contribution of this antigen to the pathogenesis. In the molecular mass range below 13 kD, no specific carbohydrate residues or phosphorylcholine-containing (PC) determinants could be identified by lectin-blotting or PC-specific immunoblotting, respectively. Two-dimensional separation and immunoblotting distinctly resolved more than 40 antigenic polypeptides, the majority focusing at acidic isoelectric points. In O. volvulus-infected chimpanzees the IgG1- and IgG4-reactivity against OvAg below 13 kD appeared concurrently with onset of patent infection. These data suggest that some of these VLMW-OvAg might be associated with the production and release of microfilariae from gravid female worms as well as be involved in immune-mediated pathogenesis during filarial infections.

Adolescent↗

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↗

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↗

PubMed1996

Viability and fertility of adult Onchocerca volvulus after 6 years of treatment with ivermectin.

Onchocerca volvulus nodules were removed from 77 fully compliant patients in a longitudinal study of ivermectin treatment in Sierra Leone. The patients had participated in a randomized controlled trial and received either 4 annual doses of ivermectin or 10 6-monthly doses over 6 years. Worms were examined 9 months after the last treatment for evidence of changes in morphology, viability and reproductivity. The findings were compared with results for the 2 groups obtained at earlier surveys of the same study population. Repeated treatment at 6 and 12-month intervals has resulted in a marked ageing of the male worm population profile and a significant reduction in the proportion of live female worms found in the nodules. In addition, there has been a reduction in reproductivity of 90% or more. However, most of the worms found were still alive and potentially fertile, underlining the need for the continuation of regular ivermectin treatment to maintain the benefits achieved.

Adult↗

PubMed1997

Comparison of the use of skin scarification and skin biopsies to determine the prevalence and intensity of Onchocerca volvulus infection.

Two methods for the detection of Onchocerca volvulus microfilariae in the skin were compared in a population-based survey in Gatete, Murama and Jerama, three 'collines' (administrative units) in Burundi. Of the 513 subjects examined, each by both methods, 131 (25.5%) were found positive by skin scarification and 119 (23.2%) by membrane filtration of the fluid in which two skin snips had been incubated. Whilst the sensitivity of the two methods was similar (90% for scarifications and 82% for skin snips), more microfilariae were found by scarification than by biopsy (with geometric mean numbers of 9.1 and 4.1, respectively). Also, more of the cases with infections of low intensity (i.e. < or = 5 microfilariae detected) were found by scarification than by skin snipping (77.9% v. 60.3%; P = 0.06). The endemicity of onchocerciasis and age- and sex-specific prevalences and intensities of infection could be determined equally well using either method. The shortcomings of past comparisons between scarification and skin-snip methods are discussed. Skin scarification has many advantages for the detection of infected individuals in rural health centres and for use in population-based surveys. It may also be helpful when mixed filarial infections are present (especially where onchocerciasis and loiasis co-occur).

Adolescent↗

PubMed1993

A probable case of vertical transmission of Onchocerca volvulus microfilariae.

A probable case of vertical transmission of Onchocerca volvulus microfilariae in Dass Bauchi State, Nigeria is presented. A 28-week-old male child delivered by a 39-year-old Fulani woman suffering from onchocerciasis was positive for O. volvulus microfilariae based on skin snip examinations. The child had general body pruritic rash and intermittent fever. Although the child's skin snip on re-examination five weeks later was also positive, the fever had gradually subsided.

Adult↗

PubMed1998

Onchocerca ochengi: epidemiological evidence of cross-protection against Onchocerca volvulus in man.

In North Cameroon, the vector of Onchocerca volvulus (causative agent of human onchocerciasis) also transmits 2 filariae of animals: O. ochengi from cattle and O. ramachandrini from wart hogs. In order to assess the qualitative and quantitative roles of these 'animal filariae' in the epidemiology of O. volvulus, the transmission of the 3 parasites was measured in 2 villages and related to the endemicity of human onchocerciasis. In Galim, a cattle-farming Guinea savanna village where wild animals are rare, the overwhelming majority of all filarial infections found in the Simulium damnosum s.l. vectors throughout the year were O. ochengi (89%). The remaining infections were mainly O. volvulus (10.5%), and a few O. ramachandrini (0.5%). In Karna, a crop-farming Sudan savanna village where cattle are rare, but wild animals common, flies were also more frequently infected with animal filariae than with the human parasite. In the dry season, when nomadic cattle are present, 54% of all infections were O. ochengi, 36% O. volvulus and 10% O. ramachindrini. In the rainy season, when the cattle move away, flies were mainly infected with O. ramachandrini (52% of all infections) and secondly with O. volvulus (48%). In Karna, the relationship between the Annual Transmission Potential (ATP) of O. volvulus and its prevalence in the human population conformed to other onchocerciasis foci, in that a moderate ATP led to hyperendemic onchocerciasis. In Galim, however, a 7-fold higher O. volvulus-ATP (caused by a very high biting rate of the flies) contrasted with a strikingly low endemicity of onchocerciasis. Since, at the same time, in Galim the transmission of O. ochengi (measured on man) was very high (15,000 L3/fly collector/year), we hypothesize that the reduced endemicity of onchocerciasis in Galim is due to 'natural heterologous vaccination' by the large annual number of O. ochengi-L3, inoculated into man by anthropo-boophilic S. damnosum s.l. The importance of micro-epidemiology for the understanding of the interlinkage of human and animal onchocerciasis is discussed.

Animals↗

PubMed1994

Characterization of enzymatically active Onchocerca volvulus Cu/Zn superoxide dismutase expressed in Escherichia coli.

The Onchocerca volvulus superoxide dismutase was expressed in Escherichia coli, using a protocol designed to produce the native enzyme rather than a fusion protein. The recombinant O. volvulus superoxide dismutase (rOVSOD) was found in the cytosol of the disrupted bacteria and represented > 10% of the total bacterial protein. The enzyme was purified to homogeneity using DEAE-Sepharose chromatography, followed by phenyl-Sepharose chromatography. The rOVSOD was enzymatically active which was demonstrated by its reactivity with O2.- produced either by the xanthine-xanthine oxidase system or by stimulated eosinophils. The specific activity was determined to be 4668 U mg-1. This activity could be blocked by rabbit antiserum raised against the rOVSOD. The maximal activity was obtained upon supplementation of the bacterial growth media and enzyme buffer with copper and zinc ions. Activity characteristics in the presence of inhibitors was also characteristic of a Cu/Zn superoxide dismutase. The rOVSOD has an apparent subunit molecular mass of 16,000 in SDS-PAGE. The active enzyme behaves as a dimer of 32 kDa as determined by gel filtration.

Amino Acid Sequence↗

PubMed1991

Immunity to Onchocerca volvulus microfilariae in mice and the induction of cross-protection with O. lienalis.

Inbred CBA/Ca mice were vaccinated with Onchocerca volvulus or Onchocerca lienalis microfilariae (mf) and challenged 100 days later with the homologous or heterologous parasite. There was a major reduction in mf recoveries from immunised animals compared with controls when the sensitising and challenge infections were both of O. volvulus mf. Resistance was manifest within one week of challenge, and rose from an 87% reduction in recoveries on day 7 to a 96% reduction on day 15. Similar results were obtained for homologous sensitising and challenge infections with O. lienalis mf. Protection afforded by sensitisation with the heterologous parasite was also high, although the expression of resistance appeared to be delayed. Vaccination with O. lienalis mf led to a 45% level of cross-protection against O. volvulus at 7 days after challenge, which rose to 94% by day 15. Vaccination with O. volvulus mf stimulated cross-protection against O. lienalis at levels of 49% and 80% as measured 7 and 15 days after challenge. It is concluded that the mouse model may be of value in analysing immune responses directed against O. volvulus mf and that the cross-protection between Onchocerca species is an advantage that should be exploited in characterising the antigens involved.

Animals↗

PubMed1992

Survival of Onchocerca volvulus in nodules implanted in immunodeficient rodents.

Onchocerca volvulus is an obligate human parasite, and its study has been difficult due to an inability to maintain it outside the human host. We report the successful transplantation of onchocercomata containing living adult O. volvulus worms into immunodeficient C.B.-17.scid/scid (scid) mice or athymic rnu/rnu (nude) rats. Living, motile worms containing viable microfilariae were present in onchocercomata recovered from scid mice or nude rats for up to 20 wk, establishing a novel animal model for future investigation of O. volvulus.

Animals↗

PubMed1988

Isolation and biochemical composition of the cuticle of Onchocerca volvulus.

A preparation of the cuticle of Onchocerca volvulus was obtained by extracting worm fragments in an series of buffers with 1.5% Triton-X-100 and 3% Sodium dodecyl sulfate (SDS). Electron micrographs of worm fragments, treated with the detergents or collagenase showed that our methods had been effective in isolating the cuticle from the other organs of the parasite. The cuticular preparation was found to contain 19 different amino acids with glycine (23.4%); proline (11.23%); hydroxyproline (10%); and glutamic acid (9.4%) being the most abundant. Hydroxylysine was present in small amounts (0.04%). Total reducing sugar was determined to be 5.3 mg per gram dry weight of the preparation. The cuticular preparation was solubilized by boiling in 2-mercaptoethanol and shown by SDS-PAGE to contain at least 10 different polypeptides in the Mr range 17,000-163,000. Five of these polypeptides with apparent Mr respectively of 33,000; 67,000; 74,000, 88,500 and 114,000 were isolated by preparative gel electrophoresis and their amino acid compositions shown to be similar to that of invertebrate collagens. We conclude that the cuticle of O. volvulus contains collagen-like proteins held together by disulfide bridges.

Amino Acids↗

PubMedDate not supplied

Onchocerca volvulus breast mass: case report from Cameroon and literature review.

Onchocerca volvulus is usually associated with subcutaneous and ocular infections. Infection of the breast is rare and there are only two previous case reports. We report a case of a thirteen-year-old Cameroonian female with a left breast mass, which had a microscopic evaluation consistent with O. volvulus.

Adolescent↗

PubMedDate not supplied

Antigens of Onchocerca volvulus.

Most studies on immunologic responses to Onchocerca volvulus have employed extracts or antigens from related filarial parasites. Consequently, little is known about the nature of O. volvulus antigens. Potential antigen sources include in vitro cultures and physicochemical fractionation of O. volvulus extracts. IgE antibody responses to a wide range of antigens occur in patients with onchocerciasis, but there is little evidence of species specificity in serologic tests. Some potent allergens are released by microfilariae, but host serum proteins appear to contaminate the most reactive fractions obtained thus far. Antibody-mediated cell adherence to microfilariae of O. volvulus occurs in vitro, and both stage and species specificity have been demonstrated. Monoclonal antibodies to O. volvulus antigens have been prepared, but, unfortunately, all to date show cross-reactivity to antigens of other filarial nematodes. Circulating antigens have been detected in patients' sera; no data are available yet on the specificity of these components. Research needs include the need for species- and stage-specific reagents for immunodiagnostic assays and for investigations on immunopathogenic mechanisms in onchocercal disease.

Animals↗

PubMed1987

Chitin in egg shells of Onchocerca gibsoni and Onchocerca volvulus.

Chemical analysis of adult females of Onchocerca gibsoni gave estimated chitin contents of 200-500 micrograms (g dry weight)-1. Egg shells from both O. gibsoni and Onchocerca volvulus stained with Calcofluor white and with fluorescent wheat germ agglutinin as shown by fluorescent light microscopy, and bound gold-labelled wheat germ agglutinin as shown by electron microscopy, under conditions specific for chitin. The egg shells appeared as single electron dense layers from 50 to 85 nm in thickness. Purified chitinase digested these egg shells, leaving coiled microfilariae unattacked. We conclude that chitin is a major component of the egg shells.

Animals↗

PubMed2006

Transmission of Onchocerca volvulus and prospects for the elimination of its vector, the blackfly Simulium neavei in the Mpamba-Nkusi focus in Western Uganda.

The transmission of Onchocerca volvulus Leuckart (Spirudida: Onchocercidae) and the prospects of Simulium neavei Roubaud (Diptera: Simuliidae) vector elimination through ground larviciding were investigated in the Mpamba-Nkusi focus, western Uganda. Transmission levels and the initiated vector elimination activities were assessed to supplement the ongoing ivermectin mass distribution programme. Searches for breeding sites, adult fly catches, dissection of flies, river treatment with temephos (Abate) and a review of annual ivermectin treatment data were conducted. High levels of crab infestation with S. neavei sensu stricto immature stages were recorded; 57.9% and 100% for the Mpamba and Nyabugando river systems, respectively. The mean numbers of larvae/pupae per crab were 3.6 +/- 0.5 in the Mpamba and 20.6 +/- 1.8 in the Nyabugando systems. Pre-intervention mean biting densities were 39 and 32 flies/(man day) in 2001 and 2002, respectively, and an annual biting rate in 2001 of > 14 000. The bimodal biting pattern of S. neavei s.s. consisted of two peaks; one in the morning (09.00-10.00 hours) and one in the afternoon (14.00-15.00 hours) with a mid-day lull in biting. The infection/infective rates were 13.3%/2.8% and 16.6%/2.9% in the dissected parous flies from the Mpamba and Nyabugando river systems, respectively. Out of approximately 1000 parous flies, 129 and 109 were found to be harbouring infective larvae of Onchocerca volvulus in their heads from the Mpamba and Nyabugando river systems, respectively. In spite of the > 10 years of ivermectin treatment, at a mean coverage of 71.3%, infection remained relatively high. Ground larviciding with temephos (Abate) initiated in June and October 2002 had a significant impact. In the Mpamba river system there was a significant (P < 0.001) reduction in positive crabs from 57.9% in 2001 to 0.06% in 2003 and a decrease in the mean number of larvae/pupae per crab from 3.6 +/- 0.5 in 2001 to 0.0007 +/- 0.0001 (P < 0.002) in 2003. Similarly, in the Nyabugando river system, a significant (P < 0.001) reduction in crab infestation from 100% in 2001 to 0.06% in 2003 and a decrease in the mean number of larvae/pupae per crab from 20.6 +/- 1.8 in 2001 to 0.06 +/- 0.03 in 2003. Drastic reductions were observed in the mean number of biting flies from 3 flies/h in 2001 to 0 flies/h in 2003 and the annual biting rates fell from 14,235 flies/year in 2001 to only 730 flies/year in 2003. These data suggest that substantial progress towards the goal of S. neavei s.s. vector elimination has been made and this will enhance the ongoing ivermectin treatment in this isolated focus.

Animals↗

PubMedDate not supplied

Paper chromatography hybridization: a rapid method for detection of Onchocerca volvulus DNA amplified by PCR.

Prior studies have shown that Onchocerca volvulus DNA can be detected in skin snips and in black flies after polymerase chain reaction (PCR) with primers specific for repeated "O-150" DNA sequences. We have adapted a paper chromatography hybridization assay (PCHA) to detect amplified O-150 DNA and compared this method to two established methods, namely agarose gel electrophoresis (AGE) and hybridization enzyme-linked immunosorbent assay (ELISA). The minimum amounts of purified O-150 DNA detected by PCHA, AGE, and ELISA were 5, 10, and 2 ng, respectively. The three methods had similar estimated sensitivities for detecting O. volvulus DNA amplified from skin snips from African subjects with onchocerciasis (88%, 84%, and 91%, respectively). No false positive results were observed with skin snips from uninfected control subjects. The paper chromatography hybridization assay detects PCR products in 30 minutes without electricity or special equipment. This technology brings DNA detection a step closer to widespread use in field settings.

Animals↗

PubMed2000

Phosphocholine-containing, zwitterionic glycosphingolipids of adult Onchocerca volvulus as highly conserved antigenic structures of parasitic nematodes.

Human Onchocerca volvulus infection sera were found to recognize zwitterionic glycolipids of O. volvulus and to cross-react with those of other parasitic nematodes (Ascaris suum, Setaria digitata and Litomosoides sigmodontis). By the use of an epitope-specific monoclonal antibody, zwitterionic glycolipids of all these nematode species were observed to contain the antigenic determinant phosphocholine. A hyperimmune serum specific for arthro-series glycolipid structures reacted with the various neutral glycolipids of all these nematodes, which demonstrated that their oligosaccharide moieties belonged to the arthro-series of protostomial glycolipids. These results indicated that arthro-series glycosphingolipids carrying, in part, phosphocholine substituents, represent highly conserved, antigenic glycolipid markers of parasitic nematodes. Three glycolipid components of the O. volvulus zwitterionic fraction were structurally characterized by matrix-assisted laser-desorption/ionization time-of-flight MS, methylation analysis and exoglycosidase treatment. Their chemical structures were elucidated to be phosphocholine-6GlcNAc(beta1-3)Man(beta1-4)Glc(1-1)ceramide, GalNAc(beta1-4)[phosphocholine-6]GlcNAc(beta1-3)Man(beta1-4)Glc(1-1) ceramide and Gal(alpha1-3)GalNAc(beta1-4)[phosphocholine-6]GlcNAc(beta1-3)Man(beta 1-4)Glc(1-1)ceramide for the zwitterionic ceramide tri-, tetra- and penta-hexosides respectively. The ceramide composition was found to be dominated by 2-hydroxylated docosanoic (C(22h:0)), tricosanoic (C(23h:0)) and tetracosanoic (C(24h:0)) acids, and C(17) sphingosine (C(d17:1)) (where (h) is hydroxylated and (d) is dihydroxylated).

Animals↗