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PubMed1997

Onchocerca volvulus: comparison of field collection methods for the preservation of parasite and vector samples for PCR analysis.

In recent years, methods for the identification of the filarial worm Onchocerca volvulus and its vector, blackflies of the Simulium damnosum complex (S. damnosum sensu lato (s.l.)), based on the amplification of parasite and vector DNA sequences with the polymerase chain reaction (PCR), have been developed. Routine application of these methods requires techniques for sample collection and preservation that are compatible with the limitations of field collection, yet preserve DNA in a form suitable for PCR. Two different methods for sample preservation were evaluated by the field collection teams and the DNA probe laboratory of the Onchocerciasis Control Programme in West Africa. The most successful involved the preservation of material from O. volvulus and its associated vectors in a dried state on microscope slides. Of over 1200 parasite samples preserved in this manner, more than 93% retained DNA yielding positive results in PCR analysis (1208/1291). Vector material (malpighian tubules and ovaries) preserved in the same manner on the same microscope slides also yielded DNA that was suitable for PCR.

Animals↗
PubMed1987

A histocytochemical study of the macrophages present in tissue responses to adult Onchocerca volvulus.

Immunocytochemical and histochemical properties of macrophages present in the subcutaneous chronic inflammatory responses surrounding adult Onchocerca volvulus (nodules) in human tissues were examined. Macrophages with strong non-specific esterase (NSE) and acid phosphatase (AcPase) activities but weak adenosine triphosphatase (ATPase) activity and HLA-DR expression (NSE+++, AcPase+++, ATPase-/+, HLA-DR-/+) were present in the centre of nodules. Many of the cells adhering to the surface of worms were NSE+++, AcPase+++, ATPase-, HLA-DR+++. The inner zone of the fibrous capsule of nodules contained macrophages with the profile NSE+++, AcPase-, ATPase-/+, HLA-DR-/+. A fourth type, NSE+++, AcPase-/+, ATPase-/+, HLA-DR+++, was located in the outer zone of the capsule, frequently within perivascular accumulations of macrophages, lymphocytes and plasma cells. Active fibroblasts were identified at the inner edge of the fibrous capsule by alkaline phosphatase staining. A feature of all nodules examined was the presence of lipid-filled macrophages, demonstrated by Oil Red O stain; these cells were usually situated in zones adjacent to the centre of nodules, and were of the NSE++, AcPase++, ATPase-/+, HLA-DR-/+ type. Lipid accumulation was not found to be related to the clinical status of the patients studied. The origin and functional significance of this lipid is unknown.

HLA-DR Antigens↗
PubMed1987

Silver enhancement of lectin-gold and enzyme-gold cytochemical labelling of eggs of the nematode Onchocerca gibsoni.

Wheat germ agglutinin-gold and chitinase-gold complexes were used to demonstrate the presence of chitin on the surfaces of eggs of the animal parasitic nematode Onchocerca gibsoni. The gold complexes were enhanced by silver intensification and examined by light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Distinctive labelling of the egg surfaces was obtained with both probes in all three microscope modes. The results indicate that the small colloidal gold markers (3-10 nm) commonly used for high resolution TEM studies may be silver enhanced and also used for sensitive LM and SEM studies.

Animals↗
PubMed1985

Onchocerca raillieti: prevalence and pathology in Sudanese donkeys.

Onchocerca raillieti was found to be prevalent in Sudanese donkeys. The parasite was reported from Central, Northern, Western and Eastern Sudan and was most predominant in the last locality. The pathological changes produced by adult worms in the ligamentum nuchae are mostly chronic and do not seem to cause any clinical manifestations. Likewise, the microfilariae, though found in high densities in the skin with a "spill over" into the eyes, produce no pathological changes in either the skin or eyes.

Animals↗
PubMed1986

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

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

Animals↗
PubMed1992

Onchocerca ochengi: Mimic, model or modulator of O. volvulus?

The cattle parasite, Onchocerca ochengi, is widely distributed in West Africa. Significantly, Simulium darnnosum, the vector o f the important human parasite, O. volvulus, the cause o f river blindness, also appears to be the vector of O. ochengi. For epidemiological reasons it is therefore vital to be able to distinguish the infective larvae o f these filoriae. Here, Sandy Trees also describes other features of the cattle parasite that make it of significance to investigations of human filariases.

Journal Article↗
PubMed1993

Molting, enzymes and new targets for chemotherapy of Onchocerca volvulus.

Parasitic nematodes do not multiply in definitive hosts, but they do molt, grow and mature for a certain period after infection, after which they devote their energies almost entirely to egg production. In this review, Sara Lustigman describes key metabolic enzymes that are essential to the development of the larval stages of Onchocerca volvulus in the host, making them potential therapeutic targets.

Journal Article↗
PubMed2005

A randomized, double-blind, controlled trial of the effects of ivermectin at normal and high doses, given annually or three-monthly, against Onchocerca volvulus: ophthalmological results.

A three-year randomized, controlled, double-blind trial was conducted in Cameroon to determine whether ivermectin, given at three-monthly intervals and/or at high doses (800 microg/kg), had a greater effect on adult Onchocerca volvulus than standard doses (150 microg/kg annually). As several patients complained of transitory subjective visual problems after treatment, some of them being of an unexpected type, we organized two series of detailed ophthalmological examinations to evaluate whether they were associated with ocular lesions. Analysis showed that these complaints were significantly more frequent in the two groups treated with high doses of ivermectin than in the reference group. In the ophthalmological examinations, the only differences recorded between the groups were a lower prevalence and mean number of microfilariae in the anterior chamber in the groups treated three-monthly, and, at the first examination round, a higher prevalence of early lesions of the iris in the group treated at high doses annually. These findings do not allow us to explain the cause of the transitory ocular complaints, nor why they were more frequent in the groups treated at high doses. However, one may conclude that using doses of ivermectin higher than the standard one should be considered with caution.

Adolescent↗
PubMed1994

The effects of Onchocerca lienalis infection on vitellogenesis in the British blackfly, Simulium ornatum.

We have previously described the major yolk protein, vitellin, in the British blackfly Simulium ornatum Meigen. Here we demonstrate that vitellogenin, synthesized in the fat body and secreted into the haemolymph, is composed of subunits with the same approximate molecular weight as vitellin, namely 200 and 68 kDa. Simulium ornatum is the natural vector for the cattle filarial nematode Onchocerca lienalis Stiles, which induces host fecundity depletion. A significant reduction in ovarian vitellin content was associated with infection by intrathoracic injection of 20 O. lienalis microfilariae immediately after blood-feeding. Fat body synthesis of vitellogenin was significantly reduced as early as 8 h post-infection in comparison with sham-injected flies. When total haemolymph protein from infected and sham injected flies was compared, titres were significantly depressed 6 h post-infection. However, later in the infection, titres were elevated by 30%, the major component being vitellogenin. The injection of dead microfilariae had no effect. An infection burden of a single parasite caused a significant reduction in ovarian protein content in comparison with shams, but no further significant decrease was observed as the parasite burden was increased from 5 to 20. Possible mechanisms underlying the disturbance of Simulium reproductive physiology are proposed.

Animals↗
PubMed1993

Onchocerca-like lesions induced by the filarioid nematode Cercopithifilaria johnstoni, in its natural hosts and in the laboratory rat.

Histo-pathological analysis of the eyes, ears, skin and associated skeletal muscles of the back of 14 animals infected with a filarioid worm with dermal microfilariae, Cercopithifilaria johnstoni: seven Rattus fuscipes, of which four were naturally infected, two marsupials, Perameles nasuta and Isodon macrourus, and five R. norvegicus. This filarioid nematode induces skin and eye lesions in all the infected animals. These lesions are similar to those described earlier with other filarioid species with dermal microfilariae, such as Monanema martini and Onchocerca volvulus; the pathogeny is similar: microfilariae live inside the lymphatic vessels and their accidental exit gives rise to a localized inflammatory reaction leading to fibrosis. C. johnstoni is particularly interesting because it may be adapted to the laboratory rat, and because the ocular lesions are severe.

Animals↗
PubMed1984

Onchocerca armillata: prevalence and pathology in Sudanese cattle.

Cattle of various ages from Khartoum Province and western Sudan were surveyed for Onchocerca armillata infection by skin snip examination and some also at post-mortem examination. The former method reliably detected infection in cattle aged between nine months and eight years. Several of the older infected animals had no microfilariae in their skin. Prevalence rate and number of microfilariae per gram of skin were higher in male than in female cattle and in animals from western Sudan than those from Khartoum province. Severe pathological changes were seen in the thoracic aorta, brachiocephalic, costocervical and brachial arteries and posteriorly in the abdominal aorta to its bifurcation into the iliac arteries.

Animals↗
PubMed1990

The transmission of onchocerciasis at a forest village in Sierra Leone. I. Simulium damnosum s.l. biting densities and infection with Onchocerca volvulus at five representative sites.

Previous studies in the forest area of Sierra Leone have shown that transmission of Onchocerca volvulus takes place many kilometers away from large breeding rivers and sometimes in open farmland. To determine where and when people in a forest village were most likely to be infected, catches of Simulium damnosum s.l. were carried out every week for 12 months, at five sites in and near a village where onchocerciasis was mesoendemic. The number of flies caught per man a day at open farm sites was significantly higher than the number caught at riverside sites. Infective flies were caught only in farmland and only during the early rainy season. The combined Annual Transmission Potential for the five sites was 129 larvae per man per year. Isoenzyme electrophoresis and morphology of biting flies identified the S. sanctipauli/soubrense subcomplex as the most common vector species. Simulium yahense and S. squamosum were sometimes present. It was concluded that the classical riverside monitoring sites do not represent high risk areas for the transmission of onchocerciasis in a forest village sited well away from the main S. damnosum s.l. breeding sites. The highest risk areas are in open farmland.

Animals↗
PubMed2002

Bacterial endosymbionts of Onchocerca volvulus in the pathogenesis of posttreatment reactions.

Treatment of onchocerciasis with diethylcarbamazine (DEC) or ivermectin is associated with a posttreatment reaction characterized by fever, tachycardia, hypotension, lymphadenopathy, and pruritus. To investigate the role of the Wolbachia bacterial endosymbiont of Onchocerca volvulus in these reactions, serum samples collected before and after treatment with either anthelmintic were assessed for evidence of Wolbachia DNA. By use of real-time quantitative polymerase chain reaction, Wolbachia DNA was detected in both groups-with significantly higher levels in those who received DEC (P <.0001). In the ivermectin group, there was a significant correlation between levels of bacterial DNA and serum tumor necrosis factor-alpha (P =.013). Peak DNA levels correlated with reaction scores (P =.048). Significant correlations were also seen between Wolbachia DNA and the antibacterial peptides calprotectin (P =.021) and calgranulin B (P <.0001). These findings support a role for Wolbachia products in mediating the inflammatory responses seen following treatment of onchocerciasis and suggest new targets for modulating these reactions.

Adolescent↗
PubMed1997

Protective responses against skin-dwelling microfilariae of Onchocerca lienalis in severe combined immunodeficient mice.

Inoculation of severe combined immunodeficient (SCID) mice with microfilariae of Onchocerca lienalis results in a sustained infection of the skin, extending for months beyond the point at which the parasites are eliminated from immunocompetent BALB/c controls. Reconstitution of SCID mice with spleen cells, thymocytes, or CD4+-cell-enriched splenocytes from naive BALB/c donors confers the ability to mount a protective immune response, leading to the rapid elimination of microfilariae. High levels of interleukin-5 and low levels of gamma interferon in the sera of reconstituted SCID mice during the destruction of microfilariae suggest that this protective immune response is directed by Th2 lymphocytes, mirroring that observed in immunocompetent controls. Unexpectedly, abbreviation of primary infections of unreconstituted SCID mice with the drug ivermectin induces resistance to reinfection with microfilariae at a level equivalent to that induced in secondarily infected, immunocompetent controls. In contrast to protection mediated by adoptive reconstitution, resistance induced by ivermectin-abbreviated infection occurs in the absence of T cells and in association with negligible levels of serum interleukin-5 and gamma interferon. This points to the activation of some alternative host defense mechanism that operates after the clearance of therapeutic levels of drug. Such a response could have important implications for the treatment of human onchocerciasis and may go some way in explaining the long-term suppression of microfilariae observed in patients after treatment with ivermectin.

Animals↗
PubMed1983

Aqueous humor and serum IgE antibody in experimental ocular Onchocerca infection of guinea pigs.

Infection of inbred Strain 2 guinea pigs by subcutaneous or intradermal injection of fresh or cryopreserved living Onchocerca lienalis microfilariae, followed by a challenge intracorneal infection of microfilariae, resulted in serum and aqueous IgE antibody and in significant corneal inflammation. Systemic or intraocular infections given separately were not sufficient to elicit IgE antibody or ocular inflammation. When intravenous transfer of pooled spleen cell suspensions from systemically infected donors to normal syngeneic recipients was substituted for the course of systemic infections, a subsequent intracorneal challenge of cell transfer recipients with microfilariae produced serum and aqueous IgE antibody. Administration of diethylcarbamazine citrate to infected animals following the intracorneal challenge resulted in increased serum IgE antibody and in increased corneal inflammation.

Animals↗
PubMed1978

Bovine onchocerciasis caused by Onchocerca armillata and O. gutturosa.

Onchocerca armillata was found in 284 (28%) of 1,016 aortas, and O. gutturosa in 82 (28.87%) of 284 nuchal ligaments and in 11 (7.85%) of 140 rumenosplenic areas in specimens from cattle slaughtered during a 12-month period. Adult parasites were not found in 600 hides. Gross lesions included parasitic tunnels, nodules, roughening and calcification in the aortic walls. The connective tissue of nuchal ligaments and rumenosplenic areas was increased in amount, was gelatinous and brown and had afew nodules, Microscopically there were acute changes with oedema, haemorrhages and cellular infiltrations predominatly by eosinophils. There were chronic granulomatous reactions characterized by accumulation of macrophages, lymphocytes, plasma cells, giant cells, calcification and fibrosis around degenerate and dead parasites. Neutral fat was in parasites and surrounding cells. Both changes often occurred in the same specimen and many samples had parasites but no tissue reaction. Hypersensitivity, foreign-body reactions and parasitic toxins apparently were involved in the genesis of these lesions.

Animals↗
PubMed2003

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

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

Journal Article↗
PubMed1975

Biopsy of Onchocerca nodules in the Igbos of Nigeria.

The occurrence of Onchocerca nodules in the Igbos of Nigeria was studied in a biopsy series. There were 90 cases in approximately 5,000 biopsies received in 4.5 years at a central laboratory. The prevalence of infection in males was 1.5 times that of females. The two youngest patients were both aged 3 years; the oldest was approximately 70 years. Of the 79 single-site biopsies, 14 (17.7%) nodules occurred on the head and 65 (82.3%) were done elsewhere. The nodules above the waist line totalled 42 (53.2%) and those below it 37 (46.8%). The favorite location was the forehead cephalically and the hip caudally. Eyelid and breast nodules were also noteworthy.

Abdomen↗