The elimination of the onchocerciasis vector from the island of Bioko as a result of larviciding by the WHO African Programme for Onchocerciasis Control

Traoré, S.; Wilson, Michael D.; Sima, A.; Barro, T; Diallo, Abdallah A.; Ake, A.; Coulibaly, Souleymane; Cheke, Robert; Meyer, Rolf; Mas, J.; McCall, Philip J.; Post, R.J.; Zoure, H. G. M.; Noma, Mounkaïla; Yaméogo, L.; Sékétéli, A.; Amazigo, Uche

doi:10.1016/j.actatropica.2009.03.007

Cited by 56 publications

(44 citation statements)

References 19 publications

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“…Regarding the former, there is a need for well-characterized long-term (individual) longitudinal data (including previous treatment history), to estimate reliably the potential macrofilaricidal effects of ivermectin. However, to avoid the potentially confounding effect of ongoing transmission (which may lead to underestimating macrofilaricidal effects, particularly under annual treatment), studies could be conducted in areas where transmission has been interrupted (in geographical or ecological islands by elimination of the local vector [58], [59]). In areas near to elimination due to ivermectin distribution alone, rates of skin repopulation by mf could be investigated by fitting models to these data under a variety of ivermectin effects assumptions.…”

Section: Discussionmentioning

confidence: 99%

Uncertainty Surrounding Projections of the Long-Term Impact of Ivermectin Treatment on Human Onchocerciasis

et al. 2013

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BackgroundRecent studies in Mali, Nigeria, and Senegal have indicated that annual (or biannual) ivermectin distribution may lead to local elimination of human onchocerciasis in certain African foci. Modelling-based projections have been used to estimate the required duration of ivermectin distribution to reach elimination. A crucial assumption has been that microfilarial production by Onchocerca volvulus is reduced irreversibly by 30–35% with each (annual) ivermectin round. However, other modelling-based analyses suggest that ivermectin may not have such a cumulative effect. Uncertainty in this (biological) and other (programmatic) assumptions would affect projected outcomes of long-term ivermectin treatment.Methodology/Principal FindingsWe modify a deterministic age- and sex-structured onchocerciasis transmission model, parameterised for savannah O. volvulus–Simulium damnosum, to explore the impact of assumptions regarding the effect of ivermectin on worm fertility and the patterns of treatment coverage compliance, and frequency on projections of parasitological outcomes due to long-term, mass ivermectin administration in hyperendemic areas. The projected impact of ivermectin distribution on onchocerciasis and the benefits of switching from annual to biannual distribution are strongly dependent on assumptions regarding the drug's effect on worm fertility and on treatment compliance. If ivermectin does not have a cumulative impact on microfilarial production, elimination of onchocerciasis in hyperendemic areas may not be feasible with annual ivermectin distribution.Conclusions/SignificanceThere is substantial (biological and programmatic) uncertainty surrounding modelling projections of onchocerciasis elimination. These uncertainties need to be acknowledged for mathematical models to inform control policy reliably. Further research is needed to elucidate the effect of ivermectin on O. volvulus reproductive biology and quantify the patterns of coverage and compliance in treated communities.

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Section: Discussionmentioning

confidence: 99%

Uncertainty Surrounding Projections of the Long-Term Impact of Ivermectin Treatment on Human Onchocerciasis

et al. 2013

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“…Pre-control studies must include mapping of vector breeding sites, testing susceptibility to insecticides, rivercarry of insecticides and determining the size of vector populations (by biting catches) (Traore et al 2009). Routine monitoring of larval-susceptibility to insecticides and adult population activity should be conducted throughout any proposed intervention by regular larval prospection and vector collection.…”

Section: Evaluating the Effect Of Larvicidingmentioning

confidence: 99%

Nodding syndrome since 2012: recent progress, challenges and recommendations for future research

Colebunders

Post

O‘Neill

et al. 2014

Tropical Med Int Health

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We aim to review the current epidemiology of nodding syndrome (NS) and discuss relevant gaps in research. NS and convulsive epilepsy of unknown aetiology are clustered within the same villages and families in onchocerciasis-endemic areas. They are therefore potentially different clinical expressions of the same disease. It has been difficult to perform full autopsies on NS patients who die in remote villages. Adequate fixation of tissue immediately after death is critical for the examination of brain tissue. Therefore, post-mortem transsphenoidal brain biopsies, performed immediately after death by trained nurses, will provide the best option for obtaining tissue for analysis. We suspect that certain blackflies in onchocerciasis-endemic areas may transmit a novel pathogen that could cause NS and epilepsy. This is supported by a recent drop in the number of new NS cases coinciding with vector control activities aimed at reducing blackfly populations in northern Uganda. We propose that metagenomic studies of human samples, blackflies and microfilariae are conducted to screen for pathogens, and that a clinical trial is planned to evaluate the impact of larviciding against NS and epilepsy epidemics.

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“…In 2005 the unique endemic Bioko form of S. yahense [25] was eradicated from the island of Bioko (formerly known as Fernando Po), Equatorial Guinea, in the Gulf of Guinea [12].…”

Section: Equatorial Guineamentioning

confidence: 99%

Factors affecting onchocerciasis transmission: lessons for infection control

Cheke

2017

Expert Review of Anti-infective Therapy

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Introduction: Onchocerca volvulus infects in excess of 15 million people. The vectors are Simulium blackflies, varieties of which differ in their ecologies, behaviour and vectorial abilities. Control of the vectors and mass administrations of ivermectin have succeeded in reducing prevalences with elimination achieved in some foci, particularly in Central and southern America. In Africa, progress towards elimination has been less successful.Areas covered: Even with community directed treatment with ivermectin (CDTI), control has been difficult in African areas with initial prevalences in excess of 55%, especially if only annual treatments are dispensed. This is partly attributable to insufficient coverage, but the appearance of incipiently resistant non-responding parasites and lack of attention to vector biology in modelling and planning outcomes of intervention programmes have also played their parts, with recrudescence now appearing in some treated areas. Expert commentary:The biology of onchocerciasis is complex involving different vectors with differing abilities to transmit parasites, diverse pathologies related to geographical and parasite variations and endosymbionts in both parasite and vector. Modelling to predict epidemiological and control outcomes is addressing this complexity but more attention needs to be given to the vectors' roles to further understanding of where and when control measures will succeed.

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The elimination of the onchocerciasis vector from the island of Bioko as a result of larviciding by the WHO African Programme for Onchocerciasis Control

Cited by 56 publications

References 19 publications

Uncertainty Surrounding Projections of the Long-Term Impact of Ivermectin Treatment on Human Onchocerciasis

Uncertainty Surrounding Projections of the Long-Term Impact of Ivermectin Treatment on Human Onchocerciasis

Nodding syndrome since 2012: recent progress, challenges and recommendations for future research

Factors affecting onchocerciasis transmission: lessons for infection control

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