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PubMed1989

Evaluation of a specific enzyme immunoassay for onchocerciasis using a low molecular weight antigen fraction of Onchocerca volvulus.

A micro-ELISA technique has been developed for the diagnosis of onchocerciasis. With the use of a low molecular weight (LMW) fraction of a soluble, adult Onchocerca volvulus extract as an antigen, the problem of nonspecificity observed with the crude worm extract is negligible. Seventy-three sera from proven cases of other filarial infections were weakly reactive or nonreactive. From cross-sectional and longitudinal surveys in a West African village hyperendemic for onchocerciasis, we concluded that this assay detects antibodies elicited when female worms start to produce microfilariae. Thirty-two of 33 children aged less than or equal to 15 years with positive skin snips were seropositive. High antibody levels could also be found in children who only became parasitologically positive 1-4 years after seroconversion. This leads to the conclusion that serology is more sensitive than the 2-snip method. In individuals with chronic infection (exposed for greater than 15 years), antibody titers were consistently lower (independent of the density of skin microfilariae) than in the early phase of a patent infection. A comparative serological study in a mesoendemic village revealed that the assay can serve to assess onchocerciasis prevalence by testing individuals aged 5-15 years.

Adolescent↗

PubMed1989

The effect of multiple ivermectin treatments on infection of Simulium ochraceum with Onchocerca volvulus.

Ivermectin, a broad spectrum antiparasitic agent, interrupted the uptake of Onchocerca volvulus microfilariae by Simulium ochraceum from a group of human volunteers given multiple oral treatments of 200 micrograms/kg body weight. Two treatments, given at 7 month intervals, resulted in almost complete suppression of developing or infective larvae in the vector population for a 6 month period. The overall decline following 2 treatments was an order of magnitude lower than the pretreatment level. Ivermectin administration, in addition to the beneficial clinical effects, also could be useful for the control of human onchocerciasis as an independent measure or in conjunction with vector control.

Adult↗

PubMed1990

Effects of multiple monthly doses of ivermectin on adult Onchocerca volvulus.

This paper assesses the effects on adult Onchocerca volvulus of monthly doses of ivermectin (150 micrograms/kg) given over 4, 8, and 12 months to patients in Guatemala. Nodules were removed 4 months after the last dose; the adult O. volvulus were extracted by collagenase digestion, studied by histological techniques, and compared with worms from untreated patients. Twelve monthly doses killed a proportion of the adult worms (12% of males and 22% of females), leaving the remainder relatively unaffected and the females slowly resuming embryogenesis. After 8 and 12 doses, a number of female worms had resumed embryogenesis in 1 genital tract only, and in 1 female a total degeneration of 1 ovary was seen. Ivermectin also led to a marked drop in the number of male worms in nodules. No serious adverse reactions occurred and the treatment was well accepted.

Animals↗

PubMed1991

Experimental Onchocerca volvulus infections in mangabey monkeys (Cercocebus atys) compared to infections in humans and chimpanzees (Pan troglodytes).

Three chimpanzees, three mangabey monkeys (Cercocebus atys), and 14 patas monkeys (Erythrocebus patas) were inoculated with L3 Onchocerca volvulus of Guatemalan origin. One chimpanzee and two mangabey monkeys developed antibody activity to at least three different antigens. Both mangabey monkeys recognized a 20 kDa antigen 3.5-5 months post-inoculation, and the monkeys and the chimpanzee developed antibody activity to 14 and 22 kDa antigens 7.5-13 months post-inoculation. One mangabey monkey and the chimpanzee became microfilaria-positive in skin snips at 16 and 21 months post-inoculation, respectively. Antibody activity to the 20 kDa antigen in the mangabey monkeys is noteworthy because of the prominence of this antigen among putatively immune persons living in onchocerciasis-endemic areas. The two mangabey monkeys responded parasitologically in a manner comparable to immune humans. No microfilariae were detected in one monkey and only scant numbers of microfilariae were observed in the second. The mangabey monkey may be a good animal model for the study of onchocerciasis.

Animals↗

PubMed1991

Comparison of the effects of a single dose and of four six-monthly doses of ivermectin on adult Onchocerca volvulus.

Adult Onchocerca volvulus worms, extracted from nodules of Guatemalans by collagenase digestion, were examined whole and by histological techniques. One group of persons received a single 150 micrograms/kg dose of ivermectin; two other groups (one with older and one with younger nodules) received four similar doses of ivermectin at 6-month intervals. For each group, there were comparable untreated controls. All nodules were removed six months after the last dose. After a single dose, the only significant difference from the controls was in the decreased proportion of female worms producing live microfilariae. After four doses, there were significant increases in the proportions of moribund/dead female worms and of live uninseminated females, when compared with the corresponding controls. There were also fewer male worms present, but this difference was not significant. Six months after the conclusion of the 4-dose regimen, the proportion of female worms producing live microfilariae was significantly lower than in the groups that had received a single dose.

Animals↗

PubMed1992

Effects of three-month doses of ivermectin on adult Onchocerca volvulus.

Onchocerca volvulus worms in nodules from Guatemalan patients treated with four, eight, or 11 single doses of ivermectin (150 micrograms/kg of body weight) that were given once every three months were examined by routine histologic techniques and compared with worms in control nodules from untreated persons living in the same location over the same time periods. All treated nodules were removed four months after the last dose of ivermectin, i.e., 13, 25, or 34 months after the start of the trial. At the 25th and 34th months, i.e., after the eighth or eleventh doses of ivermectin, there were excess mortalities in female worms of 25.5% and 32.6%, respectively, over and above the levels in controls. Furthermore, the proportions of live females still producing scanty embryos up to the gastrula stage were only 7.7% and 18.2%, and no females were producing microfilariae. Ivermectin given at 3-month intervals also reduced significantly the mean numbers of live male worms in nodules, as well as the proportions of inseminated females. This regimen was effective in preventing embryogenesis to the microfilarial stage while, at the same time, it caused a slow but steady attrition of the adult worms.

Adolescent↗

PubMed1992

The effects of repetitive community-wide ivermectin treatment on transmission of Onchocerca volvulus in Guatemala.

The effects of biannual ivermectin treatment at the community level on transmission of Onchocerca volvulus during the dry season were measured over a 30-month period in Guatemala. In the Los Tarrales Transmission Zone, an area encompassing three villages, significant changes occurred in both the prevalence and quantity of infection in the Simulium ochraceum vector population. These included a 76% reduction in females with infective stage larvae (L3S) and an 80% reduction in number of L3S per 1,000 parous flies. Significant reductions in both the mean infective biting density (IBD) and mean transmission potential (TP) also occurred. In Santa Emilia, the prevalence of infection with L3S in S. ochraceum was significantly reduced by 77% from the baseline value. The number of O. volvulus L3S per 1,000 parous flies was also reduced by 92%. Changes in both the IBD and TP were substantial but not significant due to the high degree of variance in the occurrence of O. volvulus L3S in the vector population. This was due, in part, to the movement of infected migrant workers into the finca (coffee farm). In Los Andes, four recurrent treatments successfully blocked transmission of infective stage larvae. Prevalence (flies with all stages of developing larvae) in the vector population was reduced by 89% over the two-year period; yearly reductions in both the IBD and TP were also highly significant, ultimately ending in zero values. This finding is particularly striking since prior to treatment, Los Andes exhibited the highest IBD of the three study locations and the second highest TP.

Animals↗

PubMed1995

Evaluation of alternate methods of rapid assessment of endemicity of Onchocerca volvulus in communities in southern Cameroon.

Potential diagnostic indicators of onchocerciasis (subcutaneous nodules, depigmentation or leopard skin, microfilaruria, diethylcarbamazine patch test positivity, excoriations, and pruritus) were evaluated in a rain forest region of southern Cameroon for usefulness in rapid assessment of onchocerciasis endemicity in communities. Thirty-two study villages were selected, representing high, intermediate, and low prevalence levels, and 846 adult male residents of these communities 20 or more years of age were examined according to a defined protocol. Skin snips (from each iliac crest) served as the reference standard. Skin snip positivity was 75.5%; the effect of age was minimal. Leopard skin and nodules showed the strongest correlation with both the skin snip prevalence and community microfilarial load, as reflected by the adult male study population. We selected > or = 20% nodules or > or = 20% leopard skin as the most appropriate local criteria for assigning a community to high priority for control, which corresponds to a > or = 90% skin snip prevalence in adult males. While this criteria should not be applied to regions with savannah onchocerciasis, we believe the methodology can and should be used to determine appropriate diagnostic indicators for rapid assessment of Onchocerca volvulus endemicity in regions with different dynamics of transmission and clinical expression of disease.

Adult↗

PubMed1996

Identification of Onchocerca volvulus collagen as an antigen mainly recognized by antibodies in chronic hyper-reactive onchodermatitis (sowda).

An Onchocerca volvulus expression library was differentially screened to identify a molecular marker distinguishing sowda (lichenified onchodermatitis) from other onchocerciasis forms. One clone, PG3, was recognized by pooled sera from patients with sowda, but not by pooled sera from patients with generalized onchocerciasis; it was not recognized by sera from patients with lymphatic filariasis or other helminth infections. The DNA of PG3 hybridized strongly with O. volvulus Eco RI-digested DNA, but not with DNA from Brugia spp., Trichinella spp., and humans. A weak reaction was observed with DNA from O. gibsoni and Acanthocheilonema viteae. The PG3 DNA sequence showed a high homology with both human and nematode collagens. Confirmation of the collagen-like nature of the sowda-specific PG3 product was obtained by amino terminal sequencing of the PG3 expression product, as well as by demonstrating its susceptibility to collagenase digestion. The characteristic recognition of the O. volvulus collagen specified by clone PG3 was confirmed by measuring antibody levels to the expressed product in individual sowda and generalized onchocerciasis sera, respectively. Identification of a nematode collagen antigen mainly recognized in sowda patients raises the possibility that this extreme form of dermatitis might arise through cross-reactivity between anti-O. volvulus collagen antibodies and human collagen. However, a relationship between the PG3 recognition by antibodies and the sowda pathogenesis could not be demonstrated.

Amino Acid Sequence↗

PubMed1998

A cocktail of recombinant Onchocerca volvulus antigens for serologic diagnosis with the potential to predict the endemicity of onchocerciasis infection.

We report here the evaluation of the potential of a serologic test to determine the endemicity of onchocercal infection in hyper, meso, and hypoendemic communities by the detection of antibodies to a cocktail of recombinant antigens. Parasitologic parameters of infection prevalence and intensity were compared with serologic results. Infection prevalence by serology was consistently but not significantly higher than that defined by parasitology. Differences between the communities defined by microfilarial load (CMFL) and a measurement of Onchocerca volvulus-specific antibody levels (serologic index [SI]) were similar. When stratified by age, differences were more significant in the younger age groups. If a sentinel population of 5-15-year-old individuals was used to compare communities, all could be equally ranked by serologic and parasitologic parameters. The SI of the sentinel population gave a better distinction between each community than the SI of the whole and would be sufficiently sensitive to measure the changes in endemicity that would be required for onchocerciasis control programs.

Adolescent↗

PubMed1999

Pool screen polymerase chain reaction for estimating the prevalence of Onchocerca volvulus infection in Simulium damnosum sensu lato: results of a field trial in an area subject to successful vector control.

Detection of infective parasites in the vector population can be an early indicator of recrudescence in areas freed of new cases of onchocerciasis. However, dissection of vector black flies is inefficient in areas subject to effective control. Recently, a polymerase chain reaction (PCR)-based assay has been used to detect a single Onchocerca volvulus-infected black fly in pools containing large numbers of uninfected flies. This method had not been validated on wild-caught black flies in an area subject to effective vector control. Here, we report a method of restricting the pool screen PCR assay to infectious parasites and the results of a field test in an area subject to long-term vector control. The prevalence of infection determined by dissection did not differ from that determined by pool screen PCR. The results suggest that the PCR assay may be a useful tool for epidemiologic surveillance for 0. volvulus infection.

Animals↗

PubMed1999

Induction of histamine release in parasitized individuals by somatic and cuticular antigens from Onchocerca volvulus.

The host immune response in onchocerciasis is believed to contribute to the clinical manifestations of infection. Mazzotti and chronic inflammatory reactions might be mediated by mechanisms involving specific IgE and reactivity of mast cells and basophils to the parasite antigens. In this report, we show that Onchocerca volvulus antigens are capable of inducing histamine release. Three types of extracts were prepared from the parasite: soluble total, surface, and cuticular collagen. Soluble extracts released histamine in all individuals with onchocerciasis at significantly higher levels (P < 0.05) than those found in endemic controls, but similar levels to those found in patients with mansonellosis. However, cuticular collagen induced significantly (P < 0.01) higher histamine release in patients with onchocerciasis than in those with mansonellosis. No reactivity against human type IV collagen was observed. Implications derived from the presence of sensitized basophils in the pathogenesis of onchocerciasis are discussed.

Adolescent↗

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↗

PubMed2002

Transmission intensity and the patterns of Onchocerca volvulus infection in human communities.

We focus on possible constraints upon Onchocerca volvulus establishment in humans in relation to exposure rates to infective larvae (L3) as measured by the annual transmission potential (ATP). We use mathematical and statistical modeling of pre-control west African (savanna), Mexican, and Guatemalan data to explore two hypotheses relating human infection to transmission intensity: microfilarial (mf) loads either saturate with increasing ATP or become (asymptotically) proportional to the ATP. The estimated proportion of L3 developing into adult worms ranged from 7% to 0.3% (low and high intensity areas, respectively). Relationships between mf prevalence and both mf and transmission intensity were nonlinear and statistically similar between west Africa (Simulium damnosum s.l.) and Meso America (S. ochraceum s.l.). This similarity extended to the relationship between mf intensity and ATP. The critical biting rates for onchocerciasis introduction and persistence (which depended on vector competence and host preference), were approximately 10-fold higher in settings where onchocerciasis is transmitted by S. ochraceum than in those where the vector is S. damnosum. A role for focal vector control in Mexico and Guatemala, in addition to nodulectomy and ivermectin, is suggested.

Africa, Western↗

PubMed2005

Characterisation of a heparan sulfate proteoglycan homologue OvPG-1 from Onchocerca volvulus.

OBJECTIVE: To determine the role of an immunodominant antigen OvPG-1 in human onchocerciasis. DESIGN: Cross-sectional study of subjects living in three onchocerciasis endemic areas. SETTING: Mbonge and Tubah divisions of Western Cameroon and in Esmeralda Province of Ecuador. SUBJECTS: There were 94 and 99 subjects from the Cameroon rain forest and savannah respectively, and 83 endemic residents from Ecuador. RESULTS: The IgG2 anti-OvPG-1 responses of visually impaired and microfiladermic patients were significantly higher than for their age and sex matched counterparts with normal vision and no microfiladermia (p=0.024). Furthermore, the isotype specificity of anti-OvPG-I responses varied for the various onchocerciasis endemic zones. IgG1, IgG2, IgG3 and IgE levels correlated with the presence of microfilariae in Cameroon, but not in Ecuador. CONCLUSION: Increased IgG and IgE levels to the antigen OvPG-1 seem to correlate with the development of onchocercal eye pathology. The present results suggest that the OvPG1 is a dominant antigen of Onchocerca volvulus with a significant role in the pathogenesis of onchocerciasis.

Adolescent↗

PubMedDate not supplied

[Effect of Onchocerca volvulus infestation on plasma vitamin A concentration in school children in a rural region of Cameroon].

Vitamin A deficiency is known to be associated with immune dysfunction and common childhood infections. However, little is known about the relationship between vitamin A deficiency and onchocerciasis in children. The aim of this study was to determine the prevalence of vitamin A deficiency and to investigate the relationship between vitamin A status and onchocerciasis. A total of 231 children, aged 6 to 15 years, were randomly selected between March 1995 and April 1996 at Yambassa and Balamba (central province of Cameroon). They were examined: we determined their vitamin A status and whether they had onchocerciasis. We diagnosed onchocerciasis by skin biopsy and the detection of antibodies against Onchocerca volvulus in the blood. We found that 101 of the 231 children examined (43.73%) had palpable nodules and/or microfilariae and the remaining 130 (56.27%) had been exposed to the parasite but had no clinical signs of infestation. Some children tested negative for skin microfilariae but positive by ELISA. Thus, 197 (85.28%) children were found to be infested with O. volvulus (group A) and the remaining 34 (14.72%) were found to have been exposed to the parasite but to have no clinical signs of onchocerciasis (group B). Plasma vitamin A concentrations were marginal, with concentrations below 0.7 mumol/l (20 mug/dl) recorded for 82.25% of the subjects. Children with onchocerciasis were more likely to have low vitamin A status. The mean plasma vitamin A concentration of infested children (0.52 +/- 0.14 mumol/l) was significantly lower (p < 0.05) than that of the children exposed but not infested. The parasite, O. volvulus, uses the vitamin A present in host tissues during its development, leading to a decrease in plasma retinol concentration.

Adolescent↗

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↗

PubMed2000

Impaired eosinophil recruitment to the cornea in P-selectin-deficient mice in Onchocerca volvulus keratitis (River blindness).

PURPOSE: A murine model of helminth-induced keratitis (river blindness) that is characterized by a biphasic recruitment of neutrophils (days 1-3) and eosinophils (days 3+) to the cornea has been developed. The purpose of this study was to determine the relative contribution of P- and E-selectin in recruitment of these inflammatory cells from limbal vessels to the corneal stroma. METHODS: P- and E-selectin gene knockout (-/-) mice were immunized with antigens extracted from the parasitic helminth Onchocerca volvulus. One week after the last immunization, parasite antigens were injected directly into the corneal stroma. Mice were killed on days 1 and 3 postchallenge, and eyes were immunostained with either anti-eosinophil major basic protein (MBP) or with anti-neutrophil Ab. The number of cells in the cornea was determined by direct counting. RESULTS: Recruitment of eosinophils to the cornea was significantly impaired in P-selectin(-/-) mice (63.9% fewer eosinophils on day 1 [P: = 0.0015], and 61% fewer on day 3 [P: < 0.0001]) compared with control C57BL/6 mice. In contrast, P-selectin deficiency had no effect on neutrophil recruitment to the cornea. There was no inhibition of eosinophil and neutrophil migration to the corneas of E-selectin(-/-) mice, indicating that there is no direct role for this adhesion molecule in helminth-induced keratitis. CONCLUSIONS: The present study demonstrates that P-selectin is an important mediator of eosinophil recruitment to the cornea. P-selectin interactions may therefore be potential targets for immunotherapy in eosinophil-mediated ocular inflammation.

Animals↗