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To identify the target antigens implicated in the adherence and killing of microfilariae (mf) by leucocytes, we incubated nodular mf and leucocytes in the presence of anti-cuticular monoclonal antibodies (MOVs) and fresh serum. Leucocyte donors were patients with a mean age of 37 years (with 0-1 mf/snip), who had lived in the endemic village studied for at least 10 years. After 16-20 h of incubation, up to 74% of the mf could be seen with 10 or more cells adhering to them. By 36-40 h up to 54% of the mf had been killed by the leucocytes in the presence of a cocktail of monoclonal antibodies termed MOV GIV. The degree of killing in control experiments with the monoclonal antibody MOV 1 remained lower (P less than 0.05), ranging from 0.0 to 4.5% of mf with initial viability of 90-95%. Western blotting revealed MOV GIV prominent target antigens of 10.5, 18.0, 23.5 and 27 kDa in crude surface extracts of female O. volvulus. The detected antigens may play a role in host protection.
Ivermectin is a broad spectrum anti-helminthic agent which is currently being tested for use in human onchocerciasis. Its activity is believed to result from its effect on GABA-mediated neurotransmission. We examined the effects of ivermectin on motility of microfilariae of O. volvulus following administration to humans. When ivermectin was given in dosages of 100, 150 and 200 mcg/kg on day 1 there was a clear reduction in motility of microfilariae obtained on day 3 when compared to microfilariae from the placebo group. The mean motility scores in microfilariae from ivermectin recipients were 3.1, 2.3, and 2.2 at 0, 12, and 24 hours of incubation compared to 3.3, 2.9, and 2.5, respectively, in microfilariae from placebo recipients (p less than 0.003, p less than 0.005, and p less than 0.012, respectively). Examination of the effect according to dose suggested a dose-response relationship. Microfilariae in the anterior chamber of the eye 2 days after a single oral dose of ivermectin showed abnormal and reduced winding and coiling. Microfilariae in 50% of ivermectin recipients showed abnormal motility compared to no such effects in subjects examined concurrently who received oral DEC, DEC lotion or placebo. These observations indicate that ivermectin has an effect on motility of microfilariae of O. volvulus following administration to humans.
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Thirty adult male nodule carriers from a hyperendemic onchocerciasis area in the Liberian rain forest were treated with high doses of diethylcarbamazine (30 mg/kg/d) over one week. Another ten patients received placebo tablets and served as a control. All detectable nodules were removed from half of the patients at two months and from the remaining patients at ten months after chemotherapy. The adult worms in the nodules were examined for pathological alterations by the collagenase technique including embryogram, and by histology. No macrofilaricidal effect was observed at either time, and no significant reduction of microfilariae in the uteri of the female worms or in the tissue of the nodules was seen. Two months after the therapy there was a significant increase of degenerated stretched intrauterine microfilariae but this effect was no longer observed after ten months. No pathological effect was seen on the intrauterine coiled microfilariae. On the contrary, their number had significantly increased after ten months which could mean a stimulation of the embryogenesis. No effect on spermatogenesis was observed. Both techniques, the collagenase digestion and the histological examination of the nodules, provided similar results to demonstrate that there was no marked long lasting effect on O. volvulus after a treatment with high doses of diethylcarbamazine.
In this trial suramin, diethylcarbamazine, trichlorphon, levamisole, mebendazole, melarsonyl potassiu, Hoechst 33258 and tinidazole were administered to cattle infected with O. gibsoni and O. gutturosa to determine the usefulness of this screen in predicting the effect of drugs in man against. O. volvulus except for melarsonyl potassium which was macrofilarticidal against O. gutturosa but not O. gibsoni when cattle were slaughtered 6 weeks after treatment. It was concluded that cattle infected with O. gibsoni are a satisfactory substitute for chimpanzees infected with O. volvulus, as a tertiary screen for drugs against O. volvulus, but that their use would be restricted to centres in O. gibsoni endemic areas where the necessary facilities and specialised knowledge required to use cattle as experimental animals exist.
A study was undertaken to determine whether significant variations occur in the quantitative assessment of onchocercal microfilarial densities when different methods of treating skin snips are used. The results show that teasing of the snip should be avoided because it reduces the sensitivity of the method.
Diffusion chambers containing vector-derived infective larvae of O. volvulus were implanted into male Mastomys natalensis and removed after periods up to 100 days. Nearly all chambers contained motile living parasites. After two weeks lengths and diameters of the larvae had increased significantly and after 100 days one juvenile worm showed well developed papillae at the posterior end.
Migration of human peripheral blood granulocytes in response to microfilariae of O. volvulus was demonstrated using modified Boyden chambers. Granulocyte migration was significantly enhanced when microfilariae were preincubated with heat-inactivated immune serum (delta IS), then added to a fresh serum source (P less than 0.025). This effect was not seen when microfilariae were incubated in medium alone, in delta IS alone, in delta IS plus C4-deficient guinea-pig serum, or in fresh serum alone. There was no significant difference between the response of cells from O. volvulus-infected donors and that of cells from normal volunteers. Likewise, there was no significant difference between the migratory response seen toward nodule- versus skin-derived microfilariae. These results suggest that the host inflammatory response to O. volvulus microfilariae is mediated in part by chemotactic factors generated by antibody and complement interaction with the organism and, furthermore, that these factors are product(s) of classical complement pathway activation.
Microfilariae of O. volvulus were purified from dissected nodules by centrifugation on discontinuous Percoll density gradients. Nodules were used freshly or after cryopreservation in liquid nitrogen. Highly purified and motile microfilariae were recovered from a layer of a density of 1.090 g/ml. The isolated microfilariae retained their motility up to 3 days when cultured in vitro.
The concentration of microfilariae in the skin over and at distance sup to 10 cm from the onchocercal nodule was studied in eight patients with established onchocerciasis. In spite of wide variations in microfilarial counts from snips taken from the same patient no significant differences were found in respect of distance or direction from the nodule. It is concluded that microfilariae are uniformly distributed in the skin around and onchocercal nodule in established infections.