Culture systems for the maintenance and development of microfilariae.
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Antibody-mediated mechanisms that could be important in controlling microfilaraemia in Loa loa infected amicrofilaraemic adults (mf-ve) were studied. These subjects were selected as having a verified ocular passage of an adult L. loa but being amicrofilaraemic and without recent diethylcarbamazine treatment. Sera from 37 mf-ve subjects were compared to 14 sera from heavily (greater than 4000 mf/ml) infected subjects (mf+ve) and 9 sera from Caucasian control subjects for their reactions with L. loa mf (mf). Many mf-ve sera (22/37) were strongly positive in immunofluorescence (IFAT) on living mf. Mf+ve sera were negative, or only weakly positive, and Caucasian sera were negative. Clinical signs were not significantly different between IFAT reactive and non-reactive mf-ve subjects. Approximately half of the IFAT positive, mf-ve sera were also able to agglutinate mf; no other sera were active in this test. Titres ranged from log2 3-6 and in most cases, 9/11, the agglutination reaction was mercaptoethanol-sensitive. Antibody-dependent cellular adherence was studied using mf and leukocytes from uninfected donors. Using cryopreserved mf many heat-inactivated mf-ve sera gave strong reactions with obvious adherence by 4 h and few motile mf remained by 16 h but when fresh mf were employed these reactions were weak. However, addition of complement to many (10/11) mf-ve sera considerably enhanced adherence to fresh mf. The effect of various treatments on the complement source indicated a role for both the classical and alternative pathways. The cells attached to mf were mainly neutrophils (83%) with some eosinophils (15%) and few mononuclear cells (2%). The common occurrence of antibodies able to mediate complement-dependent adherence of polymorphonuclear leukocytes to L. loa mf in the sera of mf-ve subjects may indicate that such a mechanism is important in controlling microfilaraemia in vivo.
OBJECTIVES: To determine the efficacies of combinations of ivermectin or diethylcarbamazine and albendazole, which are recommended for use in mass treatment programmes against lymphatic filariasis. METHOD: Review of published trends in microfilarial (mf) intensities after treatment with these combination therapies. By fitting a mathematical model of treatment effects to the trial data, we quantified the efficacy of treatment, distinguishing between the killing of mf (mf loss) and a reduction in mf production by adult worms (worm-productivity loss). After diethylcarbamazine-albendazole treatment mf density dropped immediately, then slowly but steadily decreased further (four trials). After ivermectin-albendazole treatment, mf densities immediately dropped to near-zero levels, followed by a small increase (five trials). For diethylcarbamazine-albendazole treatment the average mf loss was approximately 83% (ranging from 54% to 100% in the different studies) and worm-productivity loss was 100% (in all studies). For ivermectin-albendazole treatment, average mf loss was 100% (ranging from 98% to 100%) and worm productivity loss was 96% (ranging from 83% to 100%). The effects were dose-dependent. Sensitivity analysis showed that the estimates did not depend on assumptions on worm lifespan or premature period and little on assumptions on mf lifespan. CONCLUSION: The two therapies differ with respect to their direct effect on mf, but both are highly effective against adult worms. If mass treatment with these combination therapies achieves high coverage, they can have a large impact on lymphatic filariasis transmission.
Bioko is the only island known in the world with endemic onchocerciasis. The island's rural communities consist of villages and cocoa plantations inhabited by Bubi and Fang ethnic groups. The aim of this study was to evaluate the impact of 8 years of vertical ivermectin distribution on the prevalence and intensity of Onchocerca volvulus infection in the rural population by means of pre- (1989) and post-long term treatment (1998) epidemiological surveys. In both surveys, the entire population of 12 randomly selected communities (1723 and 1082 individuals) was examined. The mean ivermectin therapeutic coverage for the 8 years was 53.2%. Iliac crest skin snips were used for differential diagnosis between O. volvulus and Mansonella streptocerca. The crude O. volvulus infection prevalence before ivermectin intervention was 74.5% (1284/1723); after the intervention it was 38.4% (415/1082). The Community Microfilarial Load (CMFL) before and after ivermectin intervention was 28.29 microfilariae/snip vs. 2.32 microfilariae/snip. The reduction in prevalence and CMFL after eight annual rounds of ivermectin treatment corroborates the drug microfilaricidal activity and good tolerability. In the pre-treatment survey, the prevalence was higher in the Bubi group (77.1%, 1126/1461); post-treatment it was higher among the Fang (51.1%, 92/180). The reduction in prevalence and intensity of O. volvulus infection differed between ethnic groups and communities.
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