Progress towards onchocerciasis elimination in the participating countries of the African Programme for Onchocerciasis Control: epidemiological evaluation results

Abstract

BackgroundThe African Programme for Onchocerciasis Control (APOC) was created in 1995 to establish community-directed treatment with ivermectin (CDTi) in order to control onchocerciasis as a public health problem in 20 African countries that had 80 % of the global disease burden. When research showed that CDTi may ultimately eliminate onchocerciasis infection, APOC was given in 2008 the additional objective to determine when and where treatment can be safely stopped. We report the results of epidemiological evaluations undertaken from 2008 to 2014 to assess progress towards elimination in CDTi areas with ≥6 years treatment.MethodsSkin snip surveys were undertaken in samples of first-line villages to determine the prevalence of O. volvulus microfilariae. There were two evaluation phases. The decline in prevalence was evaluated in phase 1A. Observed and model-predicted prevalences were compared after correcting for endemicity level and treatment coverage. Bayesian statistics and Monte Carlo simulation were used to classify the decline in prevalence as faster than predicted, on track or delayed. Where the prevalence approached elimination levels, phase 1B was launched to determine if treatment could be safely stopped. Village sampling was extended to the whole CDTi area. Survey data were analysed within a Bayesian framework to determine if stopping criteria (overall prevalence <1.4 % and maximum stratum prevalence <5 %) were met.ResultsIn phase 1A 127 665 people from 639 villages in 54 areas were examined. The prevalence had fallen dramatically. The decline in prevalence was faster than predicted in 23 areas, on track in another 23 and delayed in eight areas. In phase 1B 108 636 people in 392 villages were examined in 22 areas of which 13 met the epidemiological criteria for stopping treatment. Overall, 32 areas (25.4 million people) had reached or were close to elimination, 18 areas (17.4 million) were on track but required more years treatment, and in eight areas (10.4 million) progress was unsatisfactory.ConclusionsOnchocerciasis has been largely controlled as a public health problem. Great progress has been made towards elimination which already appears to have been achieved for millions of people. For most APOC countries, nationwide onchocerciasis elimination is within reach.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-016-0160-7) contains supplementary material, which is available to authorized users.

Still mesoendemic onchocerciasis in two Cameroonian community-directed treatment with ivermectin projects despite more than 15 years of mass treatment

“…Nevertheless, new evidence points exist towards the possibility of successful elimination of river blindness in Africa using ivermectin solely [21, 22]. Indeed, a spectacular decrease in microfilaridermia prevalence below 1 % was reported in Mali and Senegal [22], as well as in some CDTI-project in the APOC countries [23, 24]. However, despite more than 20 years of disease control, onchocerciasis remains a major concern for several endemic countries, including Cameroon [25].…”

“…However, despite more than 20 years of disease control, onchocerciasis remains a major concern for several endemic countries, including Cameroon [25]. Indeed, recent WHO/APOC surveys conducted in 2011 revealed onchocerciasis prevalences above 60 % in the Centre 1, Littoral 2 and West CDTI-projects in Cameroon [24]. The reasons for the persistence of the infection are yet to be elucidated, and it is not clear whether this is due to low treatment coverage, systematic non-compliance of a proportion of the population, or suboptimal response of the parasite to ivermectin [26–28].…”

Genome-wide analysis of ivermectin response byOnchocerca volvulusreveals that genetic drift and soft selective sweeps contribute to loss of drug sensitivity

“…The success of CDTI in the majority of areas in Africa where CDTI has been implemented with good coverage [17], suggests that the alleles responsible for SOR are not common across Africa and that CDTI can interrupt transmission in many populations, depending on epidemiological and programmatic factors such as the intensity of blackfly biting on humans and the frequency and achieved coverage of CDTI [28, 33, 98–100].…”

Ivermectin: enigmatic multifaceted ‘wonder’ drug continues to surprise and exceed expectations

“…For most afflicted countries, nationwide Onchocerciasis elimination is within reach and there is hope that the global elimination target of 2025 will be achieved. 23 Latest models indicate that if the 2025 target (or sooner) is to be achieved, 1.15 billion more treatments will be required, 24 assuming that the absence of drug resistance continues.…”