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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↗
PubMed1993

Onchocerca volvulus: monoclonal antibodies to immune complex-associated parasite antigens.

Improved methods for diagnosis of onchocerciasis are needed. We have recently identified immune complex-associated parasite antigens in sera from onchocerciasis patients. The goal of this study was to produce monoclonal antibodies to these antigens that might be used in antigen detection assays. Two monoclonal antibodies (OV-1 and OV-5) that bind to parasite antigens in immunoblots of PEG-precipitated immune complexes from human onchocerciasis sera and to corresponding antigens in adult worm extracts and excretory-secretory products were produced. The target epitopes of the monoclonals are heat stable, resistant to trypsin, and destroyed by Pronase. The two monoclonals produce similar but not identical patterns of binding to immunoblots of Onchocerca volvulus adult worm antigen with major bands at 43-47, 58-63, and 70 kDa. OV-1 and OV-5 appear to bind to two distinct but closely related epitopes, neither of which is phosphorylcholine. Immunoelectron microscopy showed that the epitopes recognized by these monoclonals are widely distributed in adult female worms, but concentrated in the uterus and intestine. Antigen assays based on these antibodies detected parasite antigen in 9 of 14 sera from onchocerciasis patients, but significant background signal was detected in some nonendemic human sera. Thus, although this study has provided new information on parasite antigens in sera from onchocerciasis patients, additional work will be needed to achieve the goal of producing a sensitive and specific antigen diagnostic test for onchocerciasis.

Animals↗
PubMed1991

Onchocerca volvulus: application of the polymerase chain reaction to identification and strain differentiation of the parasite.

Previous studies have demonstrated that the genome of Onchocerca volvulus contains a variable tandemly repeated DNA sequence family with a unit length of 150 bp. The variability of the 150-bp family has been exploited to develop O. volvulus strain and species specific DNA probes. Application of these DNA probes to the study of the epidemiologically most significant life cycle stages of the parasite has been confounded by several obstacles. These include the relative insensitivity of some of the DNA probes and the difficulty in releasing genomic DNA from infective larvae and skin microfilariae in a form that may be directly detected by hybridization to the probes. DNA sequence comparison of 18 known examples of the 150-bp repeat has been used to develop two populations of degenerate oligonucleotides. These oligonucleotides have been shown to support the amplification of the 150-bp repeat family from Onchocerca DNA, using the polymerase chain reaction. Both strain and species specific members of the repeat family are faithfully amplified, allowing characterization of a parasite on the basis of hybridization of the PCR amplification products to the previously developed DNA probes. This method is shown to be applicable to all diagnostically important forms of the parasite, including adults, infective larvae, and skin microfilariae. In addition, the method is capable of detecting O. volvulus infective larvae directly in extracts of blackfly vectors.

Animals↗
PubMedDate not supplied

[Vector capacities of Similium damsnosum s.l and risk for Onchocerca volvulus transmission in Inga (Democratic Republic of Congo)].

This article analyzes the results of a one-year entomological survey conducted near the Yalala rapids in the Inga region, Democratic Republic of Congo, prior to the implementation of Community-Directed Treatment with Ivermectin (CDTI). A vector control program had been undertaken from October 1969 to December 1980, 20 kilometers upstream from the study site. The results of the present study show that during 122 collection days, 5,824 females were captured, of which 3,899 were dissected; 2,001 (51.3%) were parous while 44 (2.2%) were infected while 4 (0.2%) were infective. The crude Annual Transmission Potential (ATP) was 65 infective larvae per man and per year at the river as against 12 in Yalala village located two kilometers from the rapids. The average biting rate was 5 flies/man/day during the dry season and 90 during the rainy season. The vector capacity of similium shows that the risk of transmission of Onchocerca volvulus to the human population was not only reduced in time (2-3 months), but was also negligible all year round.

Animals↗
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↗
PubMed2004

Impact of four years of large-scale ivermectin treatment with low therapeutic coverage on the transmission of Onchocerca volvulus in the Mbam valley focus, central Cameroon.

The extent to which ivermectin treatments have an impact on onchocerciasis transmission is a matter of some concern. We investigated this issue in the Mbam valley, a hyperendemic focus located in a forest-savannah mosaic area of Cameroon. Parasitological examinations of 5-9-year-old children, who had never received any antifilarial drug, were conducted before the first distribution of ivermectin in 1991-1993 and again in 2002, after four annual rounds of mass treatments. After matching for gender, age and village of residence, the prevalence and intensity of microfilaridermia corresponded respectively, in 2002, to 66.2 and 42.0% of the initial values. The decrease was more marked among the youngest children who, compared with the older ones, were submitted to the reduced force-of-infection earlier in their life. The results of the present study suggest that the specific vectorial competence of Simulium squamosum cytotype B, the vector of Onchocerca volvulus in the Mbam valley, allows a significant decrease in onchocerciasis transmission after several years of treatment, despite low therapeutic coverage. Though these results are encouraging, efforts should be made to improve the therapeutic coverage in the area.

Animals↗
PubMed1985

Quantitative studies on the transmission of Onchocerca volvulus by Simulium damnosum s.l. in the Tukuyu Valley, South West Tanzania.

A survey of the Simulium breeding and the transmission of Onchocerca volvulus was carried out in and around the Tukuyu valley, S.W. Tanzania, S. damnosum s.l. was found breeding in the midstretches of the main rivers in the valley and their bigger tributaries, and also in the boundary river to Malawi and the most northerly of the three rivers draining the Livingstone Mts. to Lake Nyasa (L. Malawi). A total of 19,500 S. damnosum s.l. females was caught and 13,200 dissected. The annual biting rate varied between 2,000 and 23,800. 7.6% of all the flies were infected with O. volvulus and 1.5% carried infective larvae in the head capsule, on average 2.7 per fly. The transmission was mainly in the dry season and the annual transmission potential varied between 0 and 1,120. The entomological data showed many similarities to those from the Mahenge Mts., Tanzania, and correlation of places with comparable transmission potentials suggests a similarity in the relationship parasite-human host between the West African rain forest and the two Tanzanian foci.

Animals↗
PubMed1987

Population dynamics of Onchocerca volvulus after 7 to 8 years of vector control in West Africa.

In an attempt to describe the changing population dynamics of Onchocerca volvulus during a period of vector control, nodulectomies were undertaken in 256 patients from ten villages in the Onchocerciasis Control Programme (OCP) and in 74 patients from two villages in an area with ongoing transmission. A total of 1198 nodules were excised and 4350 adult worms were isolated and examined for viability and productivity. In the OCP villages, the worm population is ageing and dying without replacement by new generations of parasites and various findings signal a breakdown of the worm population after about 12 years interruption of transmission. The sexual activity of the worms was significantly reduced. A Productivity Index was developed to measure the microfilariae production at the nodule level. The reduction in this index for the OCP villages correlates closely with the decline over the control period in the community microfilarial loads in the skin. The results show that it is not only the longevity of the parasite which will determine the duration of vector control, but that the reduced productivity of the ageing parasite population is of equal importance.

Africa, Western↗
PubMed1986

Onchocerca volvulus: enzyme polymorphism in relation to the differentiation of forest and savannah strains of this parasite.

Isozyme analysis was carried out on Onchocerca volvulus worms collected from Liberia, Ivory Coast, Burkina Faso and Sudan to see whether this technique could detect differences between forest and savannah populations of this parasite. A total of 243 forest and 189 savannah individual female worms were electrophoresed and stained for seven enzymes. Four showed some polymorphism, LDH, MDH, PGM and MPI and the other three, GAPDH, PEP and GPI were invariant. Statistical analysis of the results showed that the relative proportions of genotypes from within the different countries conformed to Hardy-Weinberg expectations. Pairwise comparisons of allele frequencies between countries showed that populations from Liberia and Ivory Coast had a very similar composition; there was some divergence between all the other pairs of populations and the genetic distance was calculated to summarize the degree of divergence. The number of loci examined was small and the genetic distances were within the range expected for separate geographical populations of the same species. The usefulness of this technique in worm identification is discussed.

Alleles↗
PubMed1993

An immunohistochemical analysis of onchocercal nodules: evidence for an interaction between macrophage MRP8/MRP14 and adult Onchocerca volvulus.

We have used a panel of MoAbs to investigate the phenotype of macrophages and other leucocytes infiltrating onchocercal nodules. Nodules were removed from individuals at the end of the second year of a community-based, placebo-controlled trial of annual ivermectin chemotherapy in northern Nigeria. No significant differences were seen in the distribution and phenotype of leucocytes in nodules from ivermectin- and placebo-treated individuals. Live adult worms were only seen in nine of the 21 nodules examined. Three regions were clearly discernible within nodules containing both live and dead worms; an outer fibrovascular capsule (zone A), an inner adult worm bundle with surrounding hyaline extracellular matrix interspersed with solitary cells (zone B), and a dense cellular infiltrate surrounding and in contact with a variable proportion of the worm (zone C). Macrophages were the predominant cell type in all zones of the nodule. Those in zone B were distinguished by their dendritic morphology and strong reactivity with MoAbs directed against class II molecules, FcRI (CD64) and CD68, whereas macrophages in zone C were larger, more heterogeneous in shape, and were distinguished by strong reactivity with MoAbs directed against CR4 (CD11c, CD18) and MRP8/MRP14, and with MoAb24. T cells were found primarily in zones A and C, whilst eosinophils were found in only six nodules. A unique staining pattern was seen using MoAbs reacting with the calcium-binding protein MRP8/MRP14. Most macrophages in zones A and B were negative; however, where the occasional positive macrophage was seen in zone B, MRP8/MRP14 was also found around the cell and on the neighbouring worm surface, giving the impression that MRP8/MRP14 was being secreted onto the adult worm. Macrophages in zone C were also MRP8/MRP14-positive, and often the whole infiltrate was surrounded with extracellular MRP8/MRP14, with greatest concentration seen adjacent to the worm. MRP8/MRP14 was not identified on the surface of microfilariae (MF) within the same nodules. Since MRP8/MRP14 was seen on the adult worm in the absence of a leucocytic infiltrate, it may have an early role to play in the immune response to Onchocerca volvulus.

Animals↗
PubMed1985

The gonotrophic cycle of wild Simulium ochraceum and the associated development of Onchocerca volvulus.

A total of 1,700 host-seeking Simulium ochraceum were allowed to feed to repletion on human volunteers heavily infected with Onchocerca volvulus and then were marked and released. Seventy-three (4.3%) of the flies were recaptured. The gonotrophic cycle of S. ochraceum, including the host seeking and oviposition phases, was approximately 74-97 hr in duration; however, for a few flies the cycle was up to an additional 24 hr in length. The frequency distribution of recaptured flies indicated that 2 gonotrophic cycles may be completed in 7-8 days. The large proportion of flies recaptured with sac-stage follicular dilatations indicates that S. ochraceum may begin to search for and can rapidly locate a new host almost immediately after oviposition. Larvae of O. volvulus were found in 15 (20.6%) of the recaptured flies. Early first stage larvae were present in host-seeking flies that had completed 1 gonotrophic cycle: 12 of 13 infected flies recaptured between 74 and 97 hr had early first stage larvae. Development of O. volvulus larvae to the infective stage was estimated to require approximately 11 days at the study site. During this time, S. ochraceum would normally have completed 3 gonotrophic cycles and be in the host seeking phase of a fourth at approximately 11 days after ingesting microfilariae.

Animals↗
PubMed1995

Effect of semiannual treatments of ivermectin on the prevalence and intensity of Onchocerca volvulus skin infection, ocular lesions, and infectivity of Simulium ochraceum populations in southern Mexico.

The effect of semiannual ivermectin treatment along with nodulectomy on filarial transmission levels were estimated during the three dry seasons of 1991-1993 in a hyperendemic village in southern Mexico. Parasitologic and ophthalmologic examinations were carried out every six months until five drug treatments were completed. Ivermectin mass treatment with a coverage of approximately 80% had a significant impact (P < 0.05) on the prevalence of skin infection and the mean microfilarial skin density (CMFL), which were reduced 38% and 89%, respectively. A gradual and significant (P < 0.05) decrease in the mean microfilariae number in the anterior chamber of the eye and in corneal opacities was also observed as the CMFL was reduced. After three treatments, these were reduced 84% and 69%, respectively. However, after two years of continuous intervention, no significant differences (P > 0.05) were observed in either the daily mean infective biting density and the daily mean transmission potential. This was probably due to the remaining microfilarial load provided by the untreated resident population and migrant groups. On the whole, our results confirm both the efficacy of ivermectin to alleviate the clinical manifestations of the disease and its minimal impact on Onchocerca volvulus transmission, and indicate the need both to achieve higher levels of drug coverage and to incorporate other measures to stop transmission until a macrofilaricide drug is found.

Adolescent↗
PubMed1976

Fundus lesions in the rabbit eye following inoculation of onchocerca volvulus microfilariae into the posterior segment. I. The clinical picture.

Live microfilariae of the Cameroon forest and Sudan-savanna strains of Onchocerca volvulus were inoculated into the vitreous or into the subretinal layers of the eyes of rabbits. The lesions produced are described, and are compared with those seen in control animals, which had received inocula of microfilariae-free saline supernate introduced with a similar degree of operative trauma. Control rabbits showed only minor pigment disturbance in the retina and choroid, near the healed operation scars. Infected animals showed evidence of an inflammatory process in the eye, lasting for up to 4 weeks. Fundus lesions developed following inoculation of microfilariae into the vitreous, but they were more frequent and more severe following subretinal inoculation. The lesions produced were: pallor, vascular narrowing, and flattening of the optic disc; subretinal inflammatory exudate, giving rise to a disturbance of pigment in the retinal pigment epithelium; scattered, small choroidoretinal scars, and larger circumscribed areas of choroidoretinitis, sometimes accompanied by optic atrophy. In many eyes inoculated with microfilariae the wincing reflex was lost, indicating some visual impairment. Many of the lesions were similar to those seen in human patients with onchocerciasis, but they developed much more rapidly. Microfilariae inoculated intravenously, or into the periocular tissues, were not observed to penetrate into the eye-ball.

Animals↗
PubMed1996

Chitinase genes expressed by infective larvae of the filarial nematodes, Acanthocheilonema viteae and Onchocerca volvulus.

State-specific products of 220 and 75 kDa were identified by metabolic labelling of infective larvae of the filarial nematode Acanthocheilonema viteae in ticks. Synthesis was temperature sensitive, occurring at 27 degrees C but not at 37 degrees C. These products were secreted 3-6 days after leaving the vector during post-infective development, but subsequent expression was not detected. The smaller protein with a pI of 6.2, was purified by two-dimensional electrophoresis and the N-terminal amino acid sequence was derived. This provisionally identified the protein as a chitinase, which was confirmed biochemically by glycol-chitin substrate gel electrophoresis. The polymerase chain reaction was used to amplify a product from a cDNA library of A. viteae infective larvae. The nucleotide sequence codes for a putative signal peptide of 20 amino acids and a mature protein of 504 residues (Mr 56 kDa), exhibiting 69% identity (81% similarity allowing for conservative substitutions) with the MF1 chitinase described from microfilariae of Brugia malayi. N-linked glycosylation may account for some, or all, of the discrepancy in Mr between the predicted polypeptide and the native parasite product (75 kDa). Primers based on the A. viteae sequence were used to amplify a related sequence from a cDNA library of Onchocerca volvulus infective larvae. The O. volvulus cDNA codes for a 20-amino acid signal peptide followed by 477 residues with an Mr of 54 kDa, and shares 67% identity with the A. viteae chitinase (80% similarity allowing for conservative substitutions) and 69% identity with the B. malayi MF1 molecule. It is proposed that chitinases expressed by infective stages of these filarial nematodes may play a role in ecdysis during post-infective development.

Amino Acid Sequence↗
PubMed1984

Comparison of heterologous adult Brugia malayi and homologous Onchocerca volvulus antigen in the enzyme-linked immunosorbent assay (ELISA) for Guatemalan onchocerciasis.

To determine the susceptibility of a heterologous filarial antigen for measuring Onchocerca volvulus antibodies, worms were compared using an enzyme-linked immunosorbent assay (ELISA) test. Control serum samples from helminth-free U.S. residents and from helminth-infected but filariae-free Salvadoran residents were tested and compared with serum obtained from microfilariae-positive and -negative Guatemalan residents living in an area of endemic onchocerciasis. The results showed that none of the sera from U.S. residents had positive O. volvulus ELISA titers (greater than or equal to 1:160); however, 8.51% (4/47) had positive B. malayi ELISA titers (greater than or equal to 1:640). The geometric mean titers with the B. malayi ELISA test were higher than with the O. volvulus ELISA test--in sera from 47 U.S. residents (1:219 vs. 1:49), from 108 Salvadoran residents (1:92 vs. 1:71), and from 145 microfilariae-negative (1:539 vs. 1:167) and 303 microfilariae-positive (1:1,270 vs. 1:561) Guatemalan residents. The B. malayi ELISA test exhibited slightly less sensitivity than the homologous O. volvulus ELISA test; nevertheless, a good correlation (r = 0.74) was found between the 2 test antigens, indicating that the B. malayi antigen could be used to measure O. volvulus antibodies.

Adolescent↗
PubMed1989

Effects of intermediary metabolites and electron transport inhibitors on action of chloroquine on Brugia pahangi and Onchocerca volvulus.

We examined the possibility that chloroquine is interfering with aerobic energy-generating processes in the adult filarial parasites, Brugia pahangi and Onchocerca volvulus. Using motility of these parasites as an assay of drug effect, we found that micromolar concentrations of chloroquine caused significant paralysis, but only in alkaline medium (pH 8.4). The addition of 12 mM glutamine or 10 mM albizziin to the medium completely antagonized drug-induced paralysis. In addition, in B. pahangi, all of the tricarboxylic acid cycle intermediates (10 mM) except citrate and pyruvate antagonized the effect of chloroquine on motility; in O. volvulus, oxaloacetate as well as glutamine inhibited the effect of the drug. The effect of chloroquine on both parasites was enhanced when it was used in combination with 10 microM acivicin, a glutamine antimetabolite. Here motility of B. pahangi was reduced significantly within 24-48 hr at acidic (6.8) neutral (7.4) and alkaline (8.4) pH. This effect was partially reversible by glutamine (12 mM). Motility of O. volvulus was reduced to near zero within 4 hr with this drug combination. Antimycin A and rotenone, both electron transport inhibitors, also synergized with chloroquine at any pH to produce paralysis in B. pahangi. The effects of the rotenone and chloroquine combination were reversed in the presence of 10 mM succinate. However, glutamine (12 mM) was unable to antagonize the effects of chloroquine plus antimycin A on the motility of B. pahangi. These findings suggest that chloroquine may be inhibiting aerobic energy metabolism in the filariae, possibly at the level of electron transport. Furthermore, since chloroquine is well-tolerated but only weakly filaricidal in vivo, the data indicate that use of this drug in combination with other inhibitors of aerobic energy metabolism may be a chemotherapeutically useful approach to the treatment of filariases.

Amino Acids, Diamino↗
PubMed1992

Onchocerca volvulus: immunization of chimpanzees with X-irradiated third-stage (L3) larvae.

To provide a theoretical basis for the potential development of vaccines against Onchocerca volvulus (Ov) a trial has been conducted to assess the protective efficacy of immunization of chimpanzees with X-irradiated L3 larvae. Approximately 1000 larvae were injected at 0, 1, and 7 months. The immunized animals, and unimmunized controls, were then challenged with 250 live L3. In order to provide possibly protective exposure to the immunologically distinct L4 epicuticle, a radiation dose (45 krad) was chosen which preserved about 50% of the molting ability of unirradiated larvae. Despite the presence of a strong immune response to crude adult worm extracts, and to cloned Ov antigens, at the time of challenge little or no significant protection against patent infection was observed: three of four immunized animals developed patent infection as compared to four of four controls. One immunized animal failed to become patent or to manifest the late antibody response to adult worm antigens seen in both subpatent and patent infections in this model, and may have been protected from infection. The implications of these studies for future attempts to immunize against O. volvulus are discussed.

Animals↗