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PubMed1981

Onchocerciasis diagnosis and the probability of visual loss in patients with skin snips negative for Onchocerca volvulus microfilariae.

Two methods have been used to verify the diagnosis of patients living in the onchocerciasis hyperendemic region of Liberia found to have O.v. negative skin snips. The first was based on a histological and an electronmicroscopic examination of the skin to determine whether the characteristic onchocerciasis dermatitis was absent, and to compare the results with age matched subjects having minimal to densely O.v. mf infested skin. The second method involved the skin response of patients with O.v. mf negative skin snips to topically applied DEC. No O.v. mf were found in skin snips serially sectioned and examined histologically from patients in which the results of incubation studies were completely negative. Skin snips from these seemingly O.v. mf negative patients had a dermatitis, whereas no dermatitis was found in skin snips taken from subjects living in nearby nonendemic areas. Patients with O.v. mf positive skin snips responded to DEC applied topically with increased pruritus and a papular rash whose severity was proportionate to the intensity of infestation. Patients with O.v. mf negative skin snips responded to DEC applied topically with increased pruritus and developed either a localized papular rash or widely dispersed papules; confirmation of onchocerciasis in these patients was found in the identification of O.v. mf in histological sections of the papules.

Adolescent↗
PubMed1980

Investigations on female Onchocerca volvulus for the evaluation of drug trials.

Females of O. volvulus show several typical morphological alterations during their ontogenesis. In order not to attribute such natural findings to the efficacy of drugs in drug trials female worms isolated from untreated patients in Liberia and Togo were examined by light microscopy. Local incrustations could be found regularly on the surface of the female parasite. Different inclusions are described which could often be found. They partially lead to degeneration and calcification. For the evaluation of ovocidal or embryocidal efficacy of drugs the developmental stages of 290 untreated female worms were quantitatively assessed, normal and pathologically altered forms were distinguished. Embryos were obviously not produced continuously but in intervalls of unknown length and frequency. Two third of the females contained embryos and microfilariae, one third showed eggs only or had empty uteri. The number of the developmental stages per female varied considerably. On the average more than 200,000 stages per female were found.

Animals↗
PubMed1980

Onchocerca volvulus: effect of suramin on lactate dehydrogenase and malate dehydrogenase.

Lactate dehydrogenase and malate dehydrogenases were partially purified and characterized from adult O. volvulus. The molecular weight of lactate dehydrogenase was determined to be 130 000, those of malate dehydrogenase I and II to be 120 000 and 65 000, respectively. The activities of both malate dehydrogenases and of the lactate dehydrogenase were strongly inhibited by suramin. The inhibition constants were determined to be in the range of 2 microM to 5 microM. The type of inhibition was found to be competitive with respect to the coenzyme NADH and to be non-competitive to the substrates. It is suggested that the mode of action of suramin in the therapy of Onchocerciasis might depend on the blokkade of reoxidation of NADH produced within the glycolytic pathway.

Animals↗
PubMed1980

Observations on Onchocerca gibsoni and nodule development in naturally-infected cattle in Australia.

O. gibsoni worms were extracted from 185 nodules of a total of 370 worm nodules collected from 94 naturally infected cattle at Townsville, Australia. 183 of the 185 nodules contained a single female worm, 60% of them contained a single male worm and 7% contained two male worms. Nodules containing males alone were not found. Small nodules (less than 0.2 g) contained immature female worms without microfilariae and no males. As nodule size and female worm size increased, the number of female worms with microfilariae and the number of nodules with males increased reaching almost 100% in nodules weighing greater than 3.0 g. It is suggested that female worms normally become encapsulated when young, grow within the nodule and tht the male enters the nodule later, fertilises the female and remains in the nodule.

Animals↗
PubMed1994

Onchocerca volvulus: in vitro cytotoxic effects of human neutrophils and serum on third-stage larvae.

The cytotoxic effects of neutrophils co-cultured with infective third-stage larvae (L3) and autologous serum from three groups of individuals: infected (INF), non-patent endemic normals (EN) and non-endemic controls (NEC), were compared using a MTT (3-(4,5 dimethylthiazol-2yl)-2,5 diphenyl tetrazolium bromide) reduction assay as a biochemical parameter of larval viability. The MTT assay permitted the detection of L3 which had suffered varying levels of necrosis. The observations from this study indicate that infected individuals and endemic normals are capable of mounting a specific immune response against the infective L3. This is based on our findings of i) significantly greater numbers of L3 showed necrosis in neutrophil cultures of the INF and EN compared to those from the NEC, ii) a superior ability of cultures from these individuals to inhibit the molting of L3 to fourth-stage larvae, iii) IgG antibodies reactive with the surface of L3, detected by immunofluorescence in the serum of the INF and the EN and iv) recognition of specific antigens in extracts of L3 detected by Western blot analysis. The specific immune response directed against L3 is probably a significant immunological defense mechanism used to limit infection in endemic areas.

Adolescent↗
PubMed1995

Impact of combined large-scale ivermectin distribution and vector control on transmission of Onchocerca volvulus in the Niger basin, Guinea.

As part of the WHO Onchocerciasis Control Programme in West Africa (OCP), the attack phase of operations in the Niger basin in Guinea began in 1989 with the simultaneous use of ivermectin and vector control. Larvicide applications coupled with annual large-scale ivermectin distribution have greatly reduced blackfly infectivity (by 78.8% for the number of infective larvae per 1000 parous flies). The combination of vector control and ivermectin has permitted excellent control of transmission. In the original OCP area, it took 6-8 years of vector control alone to obtain an equivalent decrease in blackfly infectivity. For the same number of flies caught, transmission was much higher in areas where ivermectin had not been distributed. The combined use of ivermectin and vector control has opened up new prospects for carrying out OCP operations with, notably, the possibility of reducing larviciding operations.

Animals↗
PubMedDate not supplied

[The effect of ivermectin on the transmission of Onchocerca volvulus in southern Mexico].

We assessed the transmission potential and the mean infected and infective biting density of S. ochraceum in an onchocerciasis endemic community in the southern Mexican state of Chiapas. In addition, the impact of first treatment of ivermectin during the peak of natural infection of host-seeking S. ochraceum populations was also evaluated. Monthly entomological sampling was carried out during the year before treatment to assess the seasonal biting behavior of parous host-seeking S. ochraceum females, and either infected (with whatever stage of O. volvulus) or infective females (with only third larval stage of O. volvulus). The mean of infective biting density was unimodal with the peak in February. Higher densities of infective females were detected from January to March. Annual infective biting density estimated was 95.2 and the annual transmission potential of 152.3. After treatment with ivermectin, entomological collections were carried out during the December-April period. In these months, the first ivermectin mass treatment produced a reduction of natural infection rates of 55 per cent in the mean infected females density (p < 0.001) and of 30 per cent in the transmission potential. However, significative differences were found in parity rates of biting females during the evaluation periods. Decrease of infection rates in vector populations was caused by immediate effect of ivermectin over the skin microfilariae. Microfilariae community load available for transmission declined significantly from 14 Dmg/mg to 5.9 Dmf/mg. These means were statistically different (p < 0.001) and were reduced by 58 per cent from the baseline value.

Animals↗
PubMed1993

Antibody responses to Onchocerca volvulus in Ecuadorian Indians and blacks.

In Ecuador, previous epidemiological studies of onchocerciasis affecting a population consisting of Blacks of African origin and Amerindians of the Chachi tribe, have demonstrated different frequencies of clinical disease manifestations in each racial group. To explore the possibility of differential antibody responses to O. volvulus antigens in this population, a subset of sera from these two groups of Ecuadorians with onchocerciasis was analyzed for antibody to O. volvulus antigens using ELISA and Western blot techniques. Significantly higher levels of immunoglobulin against O. volvulus were demonstrated in Chachi Indians compared to native Blacks of African origin: total Ig (p = 0.049), IgG (P = 0.002) IgG4 (p = 0.019) and IgA (p = 0.035). Western blot analysis of sera from 41 persons demonstrated more intense and more frequent recognition of low molecular weight parasite antigens in the Chachi compared to a similar group of male and female Ecuadorian Blacks. These data suggest that the intensity of antibody responses to O. volvulus antigens may reflect the influence of racial factors in the pathogenesis of onchocerciasis in Ecuador.

Adult↗
PubMed1993

Characterization of a variant tandem repeat from Sudanese Onchocerca volvulus.

Strategies for detection and control of onchocerciasis in Africa have included identification of DNA probes and PCR target sequences for sensitive and specific detection of parasites. To evaluate the applicability of published PCR and DNA probe based methods for the study of onchocerciasis in Sudan, we collected adult O. volvulus from geographically distinct regions of Sudan (700 miles apart), Abu Hamed (northern desert) and Raja (southwestern savannah), and we examined the similarities between Sudanese O. volvulus repeats and published versions of the repeat from West African O. volvulus. Amplification of DNA extracted from the Raja O. volvulus strain predictably generated a ladder of products, multiples of the base 150 bp repeat, as has been reported from West Africa. However, amplification of DNA from the Abu Hamed O. volvulus isolate resulted in a series of doublets. The unexpected DNA fragments thus amplified differed in size from the base 150 bp unit by approximately 50 base pairs and was most clearly visualized at 150-200 base pairs. DNA sequence analysis of the amplified repeats in the isolate of O. volvulus from Abu Hamed revealed a variant of the 150 bp tandem repeat which contained an extra 49 bp. The additional 49 bp contained two short repeats of 21 bp and 10 bp, corresponding to bases 99-119 and 128-137 respectively, of the known 150 bp O. volvulus repeat. This work demonstrates a variant of the O. volvulus 150 bp tandem repeat, which easily distinguishes Raja and Abu Hamed isolates of O. volvulus, and which has potential value for differentiating Abu Hamed strains of O. volvulus from other strains in East Africa.

Animals↗