Research for control: the onchocerciasis experience

Genome-based tools for onchocerciasis elimination: utility of the mitochondrial genome for delineating Onchocerca volvulus transmission zones

National programs in Africa have expanded their objectives from control of onchocerciasis (river blindness) as a public health problem to elimination of parasite transmission, motivated by the reduction of Onchocerca volvulus infection prevalence in many African meso- and hyperendemic areas due to mass drug administration of ivermectin (MDAi). Given the large, contiguous hypo-, meso-, and hyperendemic areas, sustainable elimination of onchocerciasis in sub-Saharan Africa requires delineation of geographic boundaries for parasite transmission zones, so that programs can consider the risk of parasite re-introduction through vector or human migration from areas with ongoing transmission when making decisions to stop MDAi. We propose that transmission zone boundaries can be delineated by characterising the parasite genetic population structure within and between potential zones. We analysed whole mitochondrial genome sequences of 189 O. volvulus adults to determine the pattern of genetic similarity across three West African countries: Ghana, Mali, and Côte d'Ivoire. Population genetic structure indicates that parasites from villages near the Pru, Daka, and Black Volta rivers in central Ghana belong to one parasite population, indicating that the assumption that river basins constitute individual transmission zones is not supported by the data. Parasites from Mali and Côte d'Ivoire are genetically distinct from those from Ghana. This research provides the basis for developing tools for elimination programs to delineate transmission zones, to estimate the risk of parasite re-introduction via vector or human movement when intervention is stopped in one area while transmission is ongoing in others, to identify the origin of infections detected post-treatment cessation, and to investigate whether persisting prevalence despite ongoing interventions in one area is due to parasites imported from others.

Ivermectin Treatment Response in Onchocerca Volvulus Infected Persons with Epilepsy: A Three-Country Short Cohort Study

Despite a long history of community-directed treatment with ivermectin (CDTI), a high ongoing Onchocerca volvulus transmission is observed in certain onchocerciasis-endemic regions in Africa with a high prevalence of epilepsy. We investigated factors associated with higher microfilarial (mf) density after ivermectin treatment. Skin snips were obtained from O. volvulus-infected persons with epilepsy before, and 3 to 5 months after ivermectin treatment. Participants were enrolled from 4 study sites: Maridi (South Sudan); Logo and Aketi (Democratic Republic of Congo); and Mahenge (Tanzania). Of the 329 participants, 105 (31.9%) had a post-treatment mf density >20% of the pre-treatment value. The percentage reduction in the geometric mean mf density ranged from 69.0% (5 months after treatment) to 89.4% (3 months after treatment). A higher pre-treatment mf density was associated with increased probability of a positive skin snip after ivermectin treatment (p = 0.016). For participants with persistent microfiladermia during follow-up, a higher number of previous CDTI rounds increased the odds of having a post-treatment mf density >20% of the pre-treatment value (p = 0.006). In conclusion, the high onchocerciasis transmission in the study sites may be due to initially high infection intensity in some individuals. Whether the decreasing effect of ivermectin with increasing years of CDTI results from sub-optimal response mechanisms warrants further research.

Urinary N-acetyltyramine-O,β-glucuronide in Persons with Onchocerciasis-Associated Epilepsy

We investigated urinary N-acetyltyramine-O,β-glucuronide (NATOG) levels as a biomarker for active Onchocerca volvulus infection in an onchocerciasis-endemic area in the Democratic Republic of Congo with a high epilepsy prevalence. Urinary NATOG was measured in non-epileptic men with and without O. volvulus infection, and in O. volvulus-infected persons with epilepsy (PWE). Urinary NATOG concentration was positively associated with microfilarial density (p < 0.001). The median urinary NATOG concentration was higher in PWE (3.67 µM) compared to men without epilepsy (1.74 µM), p = 0.017; and was higher in persons with severe (7.62 µM) compared to mild epilepsy (2.16 µM); p = 0.008. Non-epileptic participants with and without O. volvulus infection had similar NATOG levels (2.23 µM and 0.71 µM, p = 0.426). In a receiver operating characteristic curve analysis to investigate the diagnostic value of urinary NATOG, the area under the curve was 0.721 (95% CI: 0.633-0.797). Using the previously proposed cut-off value of 13 µM to distinguish between an active O. volvulus infection and an uninfected state, the sensitivity was 15.9% and the specificity 95.9%. In conclusion, an O. volvulus infection is associated with an increased urinary NATOG concentration, which correlates with the individual parasitic load. However, the NATOG concentration has a low discriminating power to differentiate between infected and uninfected individuals.

Genomic Epidemiology in Filarial Nematodes: Transforming the Basis for Elimination Program Decisions

Onchocerciasis and lymphatic filariasis are targeted for elimination, primarily using mass drug administration at the country and community levels. Elimination of transmission is the onchocerciasis target and global elimination as a public health problem is the end point for lymphatic filariasis. Where program duration, treatment coverage, and compliance are sufficiently high, elimination is achievable for both parasites within defined geographic areas. However, transmission has re-emerged after apparent elimination in some areas, and in others has continued despite years of mass drug treatment. A critical question is whether this re-emergence and/or persistence of transmission is due to persistence of local parasites-i.e., the result of insufficient duration or drug coverage, poor parasite response to the drugs, or inadequate methods of assessment and/or criteria for determining when to stop treatment-or due to re-introduction of parasites via human or vector movement from another endemic area. We review recent genetics-based research exploring these questions in Onchocerca volvulus, the filarial nematode that causes onchocerciasis, and Wuchereria bancrofti, the major pathogen for lymphatic filariasis. We focus in particular on the combination of genomic epidemiology and genome-wide associations to delineate transmission zones and distinguish between local and introduced parasites as the source of resurgence or continuing transmission, and to identify genetic markers associated with parasite response to chemotherapy. Our ultimate goal is to assist elimination efforts by developing easy-to-use tools that incorporate genetic information about transmission and drug response for more effective mass drug distribution, surveillance strategies, and decisions on when to stop interventions to improve sustainability of elimination.

Is onchocerciasis elimination in Africa feasible by 2025: a perspective based on lessons learnt from the African control programmes

BACKGROUND

Onchocerciasis is found predominantly in Africa where large scale vector control started in 1974. Registration and donation of ivermectin by Merck & Co in 1987 enabled mass treatment with ivermectin in all endemic countries in Africa and the Americas. Although elimination of onchocerciasis with ivermectin was considered feasible only in the Americas, recently it has been shown possible in Africa too, necessitating fundamental changes in technical and operational approaches and procedures.

MAIN BODY

The American programme(OEPA) operating in onchocerciasis epidemiological settings similar to the mild end of the complex epidemiology of onchocerciasis in Africa, has succeeded in eliminating onchocerciasis from 4 of its 6 endemic countries. This was achieved through biannual mass treatment with ivermectin of 85% of the eligible population, and monitoring and evaluation using serological tests in children and entomological tests. The first African programme(OCP) had a head start of nearly two decades. It employed vector control and accumulated lots of knowledge on the dynamics of onchocerciasis elimination over a wide range of epidemiological settings in the vast expanse of its core area. OCP made extensive use of modelling and operationalised elimination indicators for entomological evaluation and epidemiological evaluation using skin snip procedures. The successor African programme(APOC) employed mainly ivermectin treatment. Initially its objective was to control onchocerciasis as a public health problem but that objective was later expanded to include the elimination of onchocerciasis where feasible. Building on the experience with onchocerciasis elimination of the OCP, APOC has leveraged OCP's vast modelling experience and has developed operational procedures and indicators for evaluating progress towards elimination and stopping ivermectin mass treatment of onchocerciasis in the complex African setting.

CONCLUSIONS

Following the closure of APOC in 2015, implementation of onchocerciasis elimination in Africa appears to overlook all the experience that has been accumulated by the African programmes. It is employing predominantly American processes that were developed in a dissimilar setting from the complex African onchocerciasis setting. This is impeding progress towards decisions to stop intervention in many areas that have reached the elimination point. This article summarizes lessons learned in Africa and their importance for achieving elimination in Africa by 2025.

Alternative treatment strategies to accelerate the elimination of onchocerciasis

The use of alternative (or complementary) treatment strategies (ATSs) i.e. differing from annual community-directed treatment with ivermectin (CDTI) is required in some African foci to eliminate onchocerciasis by 2025. ATSs include vector control, biannual or pluriannual CDTI, better timing of CDTI, community-directed treatment with combinations of currently available anthelminthics or new drugs, and 'test-and-treat' (TNT) strategies requiring diagnosis of infection and/or contraindications to treatment for decisions on who to treat with what regimen. Two TNT strategies can be considered. Loa-first TNT, designed for loiasis-endemic areas and currently being evaluated using a rapid test (LoaScope), consists of identifying individuals with levels of Loa microfilaremia associated with a risk of post-ivermectin severe adverse events to exclude them from ivermectin treatment and in treating the rest (usually >97%) of the population safely. Oncho-first TNT consists of testing community members for onchocerciasis before giving treatment (currently ivermectin or doxycycline) to those who are infected. The choice of the ATS depends on the prevalences and intensities of infection with Onchocerca volvulus and Loa loa and on the relative cost-effectiveness of the strategies for the given epidemiological situation. Modelling can help select the optimal strategies, but field evaluations to determine the relative cost-effectiveness are urgently needed.

Programmatic factors associated with the limited impact of Community-Directed Treatment with Ivermectin to control Onchocerciasis in three drainage basins of South West Cameroon

INTRODUCTION

The CDTI model is known to have enhanced community participation in planning and resource mobilization toward the control of onchocerciasis. These effects were expected to translate into better individual acceptance of the intervention and hence high Treatment Coverage, leading to a sustainable community-led strategy and reduction in the disease burden. A survey revealed that after 10-12 rounds of treatment, prevalence of onchocerciasis was still high in three drainage basins of South West Cameroon and transmission was going on.

METHODS

We designed a three (3)-year retrospective (2012, 2013 and 2014), descriptive cross-sectional study to explore the roles of operational challenges in the failure of CDTI to control the disease as expected. We administered 83 semi-structured questionnaires and conducted 12 in-depth interviews with Chiefs of Bureau Health, Chiefs of Centers, CDDs and Community Heads. Descriptive statistics was used to explore indicators of performance which were supported with views from in-depth interviews.

RESULTS

We found that community participation was weak; communities were not deciding time and mode of distributions. Only 6 (15.0%) of 40 Community Drug Distributors reported they were selected at general community meetings as required. The health service was not able to meet and discuss Community-Directed Treatment with Ivermectin activities with individual communities partly due to transportation challenges; this was mostly done through letters. Funding was reported to be inadequate and not timely. Funds were not available to conduct Community-Self Monitoring after the 2014 Mass Drug Administration. There was inadequate health staff at the frontline health facility levels, and some Chiefs of Center reported that Community-Directed Treatment with Ivermectin work was too much for them. The mean operational Community Drug Distributor-population ratio was 1 Community Drug Distributor per 317 populations (range: 194-464, expected is 1:250). Community Drug Distributor attrition rate was 14% (2012), 11% (2013) and 12% (2014) of total Community Drug Distributors trained in the region. Lack of incentive for Community Drug Distributor was primary reason for Community Drug Distributor attrition. Number of Community Drug Distributors trained together by health area ranged from 14 to 127 (mean ± SD = 51 ±32) with duration of training ranging from 4-7 hours (mean ± SD = 5.05 ± 1.09). The trainings were conducted at the health centers. Community Drug Distributors always conducted census during the past three distributions (Mean ± SD = 2.85 ± 0.58). Community-Self Monitoring was facing challenge. Several of the community heads, Chiefs of Bureau Health and Chiefs of Center agreed that Community-Self Monitoring was not being carried out effectively due to lack of incentives for monitors in the communities.

CONCLUSION

Inadequate human resource, funding issues and transportation challenges during distribution periods reduced the ability of the health service to thoroughly sensitize communities and supervise CDTI activities. This resulted in weak community understanding, acceptance and participation in the process. CDTI in our study area did not achieve sustainable community-led campaign and this may have led to the reduced impact on Onchocerciasis.

O-5S quantitative real-time PCR: a new diagnostic tool for laboratory confirmation of human onchocerciasis

Background

Onchocerciasis is a parasitic disease caused by the filarial nematode Onchocerca volvulus. In endemic areas, the diagnosis is commonly confirmed by microscopic examination of skin snip samples, though this technique is considered to have low sensitivity. The available melting-curve based quantitative real-time PCR (qPCR) using degenerated primers targeting the O-150 repeat of O. volvulus was considered insufficient for confirming the individual diagnosis, especially in elimination studies. This study aimed to improve detection of O. volvulus DNA in clinical samples through the development of a highly sensitive qPCR assay.

Methods

A novel hydrolysis probe based qPCR assay was designed targeting the specific sequence of the O. volvulus O-5S rRNA gene. A total of 200 clinically suspected onchocerciasis cases were included from Goma district in South-west Ethiopia, from October 2012 through May 2013. Skin snip samples were collected and subjected to microscopy, O-150 qPCR, and the novel O-5S qPCR.

Results

Among the 200 individuals, 133 patients tested positive (positivity rate of 66.5%) and 67 negative by O-5S qPCR, 74 tested positive by microscopy (37.0%) and 78 tested positive by O-150 qPCR (39.0%). Among the 133 O-5S qPCR positive individuals, microscopy and O-150 qPCR detected 55.6 and 59.4% patients, respectively, implying a higher sensitivity of O-5S qPCR than microscopy and O-150 qPCR. None of the 67 individuals who tested negative by O-5S qPCR tested positive by microscopy or O-150 qPCR, implying 100% specificity of the newly designed O-5S qPCR assay.

Conclusions

The novel O-5S qPCR assay is more sensitive than both microscopic examination and the existing O-150 qPCR for the detection of O. volvulus from skin snip samples. The newly designed assay is an important step towards appropriate individual diagnosis and control of onchocerciasis.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2382-3) contains supplementary material, which is available to authorized users.

Insights Into Onchocerca volvulus Population Biology Through Multilocus Immunophenotyping

We have developed a serologically based immunophenotyping approach to study Onchocerca volvulus (Ov) population diversity. Using genomic sequence data and polymerase chain reaction-based genotyping, we identified nonsynonymous single-nucleotide polymorphisms (SNPs) in the genes of 16 major immunogenic Ov proteins: Ov-CHI-1/Ov-CHI-2, Ov16, Ov-FAR-1, Ov-CPI-1, Ov-B20, Ov-ASP-1, Ov-TMY-1, OvSOD1, OvGST1, Ov-CAL-1, M3/M4, Ov-RAL-1, Ov-RAL-2, Ov-ALT-1, Ov-FBA-1, and Ov-B8. We assessed the immunoreactivity of onchocerciasis patient sera (n = 152) from the Americas, West Africa, Central Africa, and East Africa against peptides derived from 10 of these proteins containing SNPs. Statistically significant variation in immunoreactivity among the regions was seen in SNP-containing peptides derived from 8 of 10 proteins tested: OVOC1192(1-15), OVOC9988(28-42), OVOC9225(320-334), OVOC7453(22-36), OVOC11517(14-28), OVOC3177(283-297), OVOC7911(594-608), and OVOC12628(174-188). Our data show that differences in immunoreactivity to variant antigenic peptides may be used to characterize Ov populations, thereby elucidating features of Ov population biology previously inaccessible because of the limited availability of parasite material.

Continental-scale, data-driven predictive assessment of eliminating the vector-borne disease, lymphatic filariasis, in sub-Saharan Africa by 2020

BACKGROUND

There are growing demands for predicting the prospects of achieving the global elimination of neglected tropical diseases as a result of the institution of large-scale nation-wide intervention programs by the WHO-set target year of 2020. Such predictions will be uncertain due to the impacts that spatial heterogeneity and scaling effects will have on parasite transmission processes, which will introduce significant aggregation errors into any attempt aiming to predict the outcomes of interventions at the broader spatial levels relevant to policy making. We describe a modeling platform that addresses this problem of upscaling from local settings to facilitate predictions at regional levels by the discovery and use of locality-specific transmission models, and we illustrate the utility of using this approach to evaluate the prospects for eliminating the vector-borne disease, lymphatic filariasis (LF), in sub-Saharan Africa by the WHO target year of 2020 using currently applied or newly proposed intervention strategies. METHODS AND RESULTS: We show how a computational platform that couples site-specific data discovery with model fitting and calibration can allow both learning of local LF transmission models and simulations of the impact of interventions that take a fuller account of the fine-scale heterogeneous transmission of this parasitic disease within endemic countries. We highlight how such a spatially hierarchical modeling tool that incorporates actual data regarding the roll-out of national drug treatment programs and spatial variability in infection patterns into the modeling process can produce more realistic predictions of timelines to LF elimination at coarse spatial scales, ranging from district to country to continental levels. Our results show that when locally applicable extinction thresholds are used, only three countries are likely to meet the goal of LF elimination by 2020 using currently applied mass drug treatments, and that switching to more intensive drug regimens, increasing the frequency of treatments, or switching to new triple drug regimens will be required if LF elimination is to be accelerated in Africa. The proportion of countries that would meet the goal of eliminating LF by 2020 may, however, reach up to 24/36 if the WHO 1% microfilaremia prevalence threshold is used and sequential mass drug deliveries are applied in countries.

CONCLUSIONS

We have developed and applied a data-driven spatially hierarchical computational platform that uses the discovery of locally applicable transmission models in order to predict the prospects for eliminating the macroparasitic disease, LF, at the coarser country level in sub-Saharan Africa. We show that fine-scale spatial heterogeneity in local parasite transmission and extinction dynamics, as well as the exact nature of intervention roll-outs in countries, will impact the timelines to achieving national LF elimination on this continent.

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

BACKGROUND

The 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.

METHODS

Skin 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.

RESULTS

In 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.

CONCLUSIONS

Onchocerciasis 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.

Research for new drugs for elimination of onchocerciasis in Africa

Onchocerciasis is a parasitic, vector borne disease caused by the filarial nematode Onchocerca volvulus. More than 99% of the population at risk of infection live in Africa. Onchocerciasis control was initiated in West Africa in 1974 with vector control, later complemented by ivermectin mass drug administration and in the other African endemic countries in 1995 with annual community directed treatment with ivermectin (CDTI.) This has significantly reduced infection prevalence. Together with proof-of-concept for onchocerciasis elimination with annual CDTI from foci in Senegal and Mali, this has resulted in targeting onchocerciasis elimination in selected African countries by 2020 and in 80% of African countries by 2025. The challenges for meeting these targets include the number of endemic countries where conflict has delayed or interrupted control programmes, cross-border foci, potential emergence of parasite strains with low susceptibility to ivermectin and co-endemicity of loiasis, another parasitic vector borne disease, which slows down or prohibits CDTI implementation. Some of these challenges could be addressed with new drugs or drug combinations with a higher effect on Onchocerca volvulus than ivermectin. This paper reviews the path from discovery of new compounds to their qualification for large scale use and the support regulatory authorities provide for development of drugs for neglected tropical diseases. The status of research for new drugs or treatment regimens for onchocerciasis along the path to regulatory approval and qualification for large scale use is reviewed. This research includes new regimens and combinations of ivermectin and albendazole, antibiotics targeting the O. volvulus endosymbiont Wolbachia, flubendazole, moxidectin and emodepside and discovery of new compounds.

River Blindness: Mathematical Models for Control and Elimination

Human onchocerciasis (river blindness) is one of the few neglected tropical diseases (NTDs) whose control strategies have been informed by mathematical modelling. With the change in focus from elimination of the disease burden to elimination of Onchocerca volvulus, much remains to be done to refine, calibrate and validate existing models. Under the impetus of the NTD Modelling Consortium, the teams that developed EPIONCHO and ONCHOSIM have joined forces to compare and improve these frameworks to better assist ongoing elimination efforts. We review their current versions and describe how they are being used to address two key questions: (1) where can onchocerciasis be eliminated with current intervention strategies by 2020/2025? and (2) what alternative/complementary strategies could help to accelerate elimination where (1) cannot be achieved? The control and elimination of onchocerciasis from the African continent is at a crucial crossroad. The African Programme for Onchocerciasis Control closed at the end of 2015, and although a new platform for support and integration of NTD control has been launched, the disease will have to compete with a myriad of other national health priorities at a pivotal time in the road to elimination. However, never before had onchocerciasis control a better arsenal of intervention strategies as well as diagnostics. It is, therefore, timely to present two models of different geneses and modelling traditions as they come together to produce robust decision-support tools. We start by describing the structural and parametric assumptions of EPIONCHO and ONCHOSIM; we continue by summarizing the modelling of current treatment strategies with annual (or biannual) mass ivermectin distribution and introduce a number of alternative strategies, including other microfilaricidal therapies (such as moxidectin), macrofilaricidal (anti-wolbachial) treatments, focal vector control and the possibility of an onchocerciasis vaccine. We conclude by discussing challenges, opportunities and future directions.

Optimization of the Esperanza window trap for the collection of the African onchocerciasis vector Simulium damnosum sensu lato

A simple inexpensive trap (Esperanza window trap) was shown recently to collect significant numbers of Simulium ochraceum sensu lato, a major vector of Onchocerca volvulus in Mesoamerica. Here, we report studies optimizing this trap for the collection of Simulium damnosum s.l., the major vector of O. volvulus in Africa. A shortened, blue and black striped version of the Esperanza window trap, when baited with a combination of CO2 and worn trousers, rivalled human landing collections in the number of S. damnosum s.l. females collected. Traps baited with a commercially available human skin lure and CO2 resulted in collections that were not significantly different than those obtained from traps baited with worn trousers and CO2. This suggests that the Esperanza window trap may offer a replacement for human landing collections for monitoring onchocerciasis transmission in Africa.

Characterizing, controlling and eliminating residual malaria transmission

Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) interventions can reduce malaria transmission by targeting mosquitoes when they feed upon sleeping humans and/or rest inside houses, livestock shelters or other man-made structures. However, many malaria vector species can maintain robust transmission, despite high coverage of LLINs/IRS containing insecticides to which they are physiologically fully susceptible, because they exhibit one or more behaviours that define the biological limits of achievable impact with these interventions: (1) Natural or insecticide-induced avoidance of contact with treated surfaces within houses and early exit from them, thus minimizing exposure hazard of vectors which feed indoors upon humans; (2) Feeding upon humans when they are active and unprotected outdoors, thereby attenuating personal protection and any consequent community-wide suppression of transmission; (3) Feeding upon animals, thus minimizing contact with insecticides targeted at humans or houses; (4) Resting outdoors, away from insecticide-treated surfaces of nets, walls and roofs. Residual malaria transmission is, therefore, defined as all forms of transmission that can persist after achieving full universal coverage with effective LLINs and/or IRS containing active ingredients to which local vector populations are fully susceptible. Residual transmission is sufficiently intense across most of the tropics to render malaria elimination infeasible without new or improved vector control methods. Many novel or improved vector control strategies to address residual transmission are emerging that either: (1) Enhance control of adult vectors that enter houses to feed and/or rest by killing, repelling or excluding them; (2) Kill or repel adult mosquitoes when they attack people outdoors; (3) Kill adult mosquitoes when they attack livestock; (4) Kill adult mosquitoes when they feed upon sugar or; (5) Kill immature mosquitoes in aquatic habitats. To date, none of these options has sufficient supporting evidence to justify full-scale programmatic implementation. Concerted investment in their rigorous selection, development and evaluation is required over the coming decade to enable control and, ultimately, elimination of residual malaria transmission. In the meantime, national programmes may assess options for addressing residual transmission under programmatic conditions through pilot studies with strong monitoring, evaluation and operational research components, similar to the Onchocerciasis Control Programme.

The geographic distribution of onchocerciasis in the 20 participating countries of the African Programme for Onchocerciasis Control: (1) priority areas for ivermectin treatment

Background

The African Programme for Onchocerciasis Control (APOC) was created to control onchocerciasis as a public health problem in 20 African countries. Its main strategy is community directed treatment with ivermectin. In order to identify all high risk areas where ivermectin treatment was needed, APOC used Rapid Epidemiological Mapping of Onchocerciasis (REMO). REMO has now been virtually completed and we report the results in two articles. The present article reports the mapping of high risk areas where onchocerciasis was a public health problem. The companion article reports the results of a geostatistical analysis of the REMO data to map endemicity levels and estimate the number infected.

Methods

REMO consists of three stages: exclusion of areas that are unsuitable for the vector, selection of sample villages to be surveyed in each river basin, and examination of 30 to 50 adults for the presence of palpable onchocercal nodules in each selected village. The survey results and other relevant information were processed in a geographical information system. A panel of experts interpreted the data taking the river-based sampling into account and delineated high risk areas where the prevalence of nodules is greater than 20%.

Results

Unsuitable areas were identified in eight countries. In the remaining areas surveys were done in a total of 14,473 sample villages in which more than half a million people were examined. High-risk areas were identified in 18 APOC countries, ranging from small isolated foci to a vast contiguous endemic area of 2 million km² running across seven countries. In five countries the high risk area covered more than 48% of the total surface area, and 31% to 48% of the population. It is estimated that 86 million people live in high risk areas in the APOC countries.

Conclusions

The REMO maps have played a significant role in onchocerciasis control in the 20 APOC countries. All high-risk areas where onchocerciasis used to be a serious public health problem have been clearly delineated. This led to the creation of community-directed treatment projects that by 2012 were providing annual ivermectin treatment to over 80 million people.

Proof-of-principle of onchocerciasis elimination with ivermectin treatment in endemic foci in Africa: final results of a study in Mali and Senegal

Background

Mass treatment with ivermectin controls onchocerciasis as a public health problem, but it was not known if it could also interrupt transmission and eliminate the parasite in endemic foci in Africa where vectors are highly efficient. A longitudinal study was undertaken in three hyperendemic foci in Mali and Senegal with 15 to 17 years of annual or six-monthly ivermectin treatment in order to assess residual levels of infection and transmission, and test whether treatment could be safely stopped. This article reports the results of the final evaluations up to 5 years after the last treatment.

Methodology/Principal Findings

Skin snip surveys were undertaken in 131 villages where 29,753 people were examined and 492,600 blackflies were analyzed for the presence of Onchocerca volvulus larva using a specific DNA probe. There was a declining trend in infection and transmission levels after the last treatment. In two sites the prevalence of microfilaria and vector infectivity rate were zero 3 to 4 years after the last treatment. In the third site, where infection levels were comparatively high before stopping treatment, there was also a consistent decline in infection and transmission to very low levels 3 to 5 years after stopping treatment. All infection and transmission indicators were below postulated thresholds for elimination.

Conclusion/Significance

The study has established the proof of principle that onchocerciasis elimination with ivermectin treatment is feasible in at least some endemic foci in Africa. The study results have been instrumental for the current evolution from onchocerciasis control to elimination in Africa.

The control of onchocerciasis, or river blindness, is based on annual or six-monthly treatment with ivermectin of populations at risk. This has been effective in controlling the disease as a public health problem but it was not known whether it could also eliminate infection and transmission to the extent that treatment could be safely stopped. Many doubted that this was feasible in Africa. A study was undertaken in three hyperendemic onchocerciasis foci with seasonal transmission in Mali and Senegal where treatment has been given for 15 to 17 years. As a result of this treatment, infection and transmission levels had fallen everywhere below postulated thresholds for elimination. Treatment was therefore stopped in each focus. Follow-up evaluations up to 5 years after the last treatment showed no evidence of recrudescence after stopping treatment but instead a consistent decline in infection and transmission levels, reaching zero in two sites. The study has established the proof-of-principle that onchocerciasis elimination with ivermectin treatment is feasible in at least some endemic foci in Africa. The results of the study have greatly contributed to the current evolution from onchocerciasis control to elimination in Africa.

Predictive and epidemiologic modeling of the spatial risk of human onchocerciasis using biophysical factors: a case study of Ghana and Burundi

Although recent efforts taken have substantially contained human onchocerciasis in many African countries, published reports indicate a recrudescence of the disease. To understand this problem, biophysical factors that favor the establishment of human onchocerciasis in Ghana and Burundi-countries identified as threat locations of recrudescence for neighboring countries-were analyzed. Data pertaining to the prevalence of human onchocerciasis in both countries was obtained from published sources. Findings in this study suggest that there was a gradient in prevalence of onchocerciasis in geographic locations near the water streams. The predictive models suggest that rainfall, humidity, and elevation were statistically significant for Burundi data while in Ghana, only the effect of elevation was highly significant (p<0.0001). In 2010, the estimated at-risk population was 4,817,280 people (19.75% of the total population) and 522,773 people (6.23% of the total population) in Ghana and Burundi, respectively. Findings can help in the effective design of preventive control measures.

Unhealthy behaviour is contagious: an invitation to exploit models for infectious diseases

We argue that the spread of unhealthy behaviour shows marked similarities with infectious diseases. It is therefore interesting and challenging to use infectious disease methodologies for studying the spread and control of unhealthy behaviour. This would be a great addition to current methods, because it allows taking into account the dynamics of individual interactions and the social environment at large. In particular, the application of individual-based modelling holds great promise to address some major public health questions.

Community-driven interventions can revolutionise control of neglected tropical diseases

Whether global health interventions target diseases (vertical), systems (horizontal) or both (diagonal), they must address the challenge of delivering services in very remote areas of poor countries with inadequate infrastructure. The primacy of this challenge has been underscored by persistent service-delivery difficulties despite several large financial commitments - the latest, US $363 million in the January 2012 London Declaration. Community-driven approaches, pioneered in river blindness control, show that engaging communities can maximise access and performance. This experience should inform a paradigm shift in disease control whereby communities are empowered to extend health service access themselves.

Impact of long-term treatment of onchocerciasis with ivermectin in Kaduna State, Nigeria: first evidence of the potential for elimination in the operational area of the African Programme for Onchocerciasis Control

Background

Onchocerciasis can be effectively controlled as a public health problem by annual mass drug administration of ivermectin, but it was not known if ivermectin treatment in the long term would be able to achieve elimination of onchocerciasis infection and interruption of transmission in endemic areas in Africa. A recent study in Mali and Senegal has provided the first evidence of elimination after 15-17 years of treatment. Following this finding, the African Programme for Onchocerciasis Control (APOC) has started a systematic evaluation of the long-term impact of ivermectin treatment projects and the feasibility of elimination in APOC supported countries. This paper reports the first results for two onchocerciasis foci in Kaduna, Nigeria.

Methods

In 2008, an epidemiological evaluation using skin snip parasitological diagnostic method was carried out in two onchocerciasis foci, in Birnin Gwari Local Government Area (LGA), and in the Kauru and Lere LGAs of Kaduna State, Nigeria. The survey was undertaken in 26 villages and examined 3,703 people above the age of one year. The result was compared with the baseline survey undertaken in 1987.

Results

The communities had received 15 to 17 years of ivermectin treatment with more than 75% reported coverage. For each surveyed community, comparable baseline data were available. Before treatment, the community prevalence of O. volvulus microfilaria in the skin ranged from 23.1% to 84.9%, with a median prevalence of 52.0%. After 15 to 17 years of treatment, the prevalence had fallen to 0% in all communities and all 3,703 examined individuals were skin snip negative.

Conclusions

The results of the surveys confirm the finding in Senegal and Mali that ivermectin treatment alone can eliminate onchocerciasis infection and probably disease transmission in endemic foci in Africa. It is the first of such evidence for the APOC operational area.

Health research systems: promoting health equity or economic competitiveness?

International collaborative health research is justifiably expected to help reduce global health inequities. Investment in health policy and systems research in developing countries is essential to this process but, currently, funding for international research is mainly channelled towards the development of new medical interventions. This imbalance is largely due to research legislation and policies used in high-income countries. These policies have increasingly led these countries to invest in health research aimed at boosting national economic competitiveness rather than reducing health inequities. In the United States of America and the United Kingdom of Great Britain and Northern Ireland, the regulation of research has encouraged a model that: leads to products that can be commercialized; targets health needs that can be met by profitable, high-technology products; has the licensing of new products as its endpoint; and does not entail significant research capacity strengthening in other countries. Accordingly, investment in international research is directed towards pharmaceutical trials and product development public-private partnerships for neglected diseases. This diverts funding away from research that is needed to implement existing interventions and to strengthen health systems, i.e. health policy and systems research. Governments must restructure their research laws and policies to increase this essential research in developing countries.

Polymerase chain reaction pool screening used to compare prevalence of infective black flies in two onchocerciasis foci in northern Sudan

Onchocerciasis remains an important debilitating disease in many areas of Africa, including Sudan. The status of infection transmission in 2007 was assessed in the vectors of two disease foci in Sudan: Abu Hamed in northern Sudan, which has received at least 10 years of annual treatment and Galabat focus in eastern Sudan, where only minor, largely undocumented treatment activity has occurred. Assessment of more than 30,000 black flies for Onchocerca volvulus infectious stage L3 larvae by using an O-150 polymerase chain reaction protocol showed that black fly infectivity rates were 0.84 (95% confidence interval = 0.0497-1.88) per 10,000 flies for Abu Hamed and 6.9 (95% confidence interval = 1.1-16.4) infective flies per 10,000 for Galabat. These results provide entomologic evidence for suppressed Onchocerca volvulus transmission in the Abu Hamed focus and a moderate transmission rate of the parasite in the Galabat focus.

Defining research to improve health systems

Robert Terry and colleagues present working definitions of operational research, implementation research, and health systems research within the context of research to strengthen health systems.

Social sciences research in neglected tropical diseases 1: the ongoing neglect in the neglected tropical diseases

Centuries of scientific advances and developments in biomedical sciences have brought us a long way to understanding and managing disease processes, by reducing them to simplified cause-effect models. For most of the infectious diseases known today, we have the methods and technology to identify the causative agent, understand the mechanism by which pathology is induced and develop the treatment (drugs, vaccines, medical or surgical procedures) to cure, manage or control.

Disease, however, occurs within a context of lives fraught with complexity. For any given infectious disease, who gets it, when, why, the duration, the severity, the outcome, the sequelae, are bound by a complex interplay of factors related as much to the individual as it is to the physical, social, cultural, political and economic environments. Furthermore each of these factors is in a dynamic state of change, evolving over time as they interact with each other. Simple solutions to infectious diseases are therefore rarely sustainable solutions. Sustainability would require the development of interdisciplinary sciences that allow us to acknowledge, understand and address these complexities as they occur, rather than rely solely on a form of science based on reducing the management of disease to simple paradigms.

In this review we examine the current global health responses to the 'neglected' tropical diseases, which have been prioritised on the basis of an acknowledgment of the complexity of the poverty-disease cycle. However research and interventions for neglected tropical diseases, largely neglect the social and ecological contextual, factors that make these diseases persist in the target populations, continuing instead to focus on the simple biomedical interventions. We highlight the gaps in the approaches and explore the potential of enhanced interdisciplinary work in the development of long term solutions to disease control.

Factors associated with compliance with community directed treatment with ivermectin for onchocerciasis control in Southwestern Ethiopia

Background

Although ivermectin is distributed free of charge through the African Programme for Onchocerciasis Control (APOC), not all eligible individuals within communities receive the annual treatment. This poses a serious threat to efforts aimed to control onchocerciasis. This study attempts to determine factors associated with compliance to Community Directed Treatment with Ivermectin (CDTI) and provides a basis for trying to understand how best to sustain long-term compliance in order to achieve success in the control of onchocerciasis.

Methods

An unmatched case-control study was conducted in Bebeka coffee plantation southwest Ethiopia. Cases were, compliant i.e., those individuals who had been registered on the relevant treatment registers and had taken all the five annual doses of Ivermectin. Controls were non-compliant, i.e. those individuals who had been recorded in the relevant treatment registers during the first treatment round(2003), and did not take at least two doses of which one being in the last treatment round (2007). Data were collected using a pre-tested interviewer administered structured questionnaire. Data were edited, cleaned, coded and analyzed using SPSS version 12.0.1 for Microsoft Windows. Multiple logistic regression models was used to identify factors associated with compliance to ivermectin.

Results

From the total of 456 individuals selected for administration of the survey questionnaire, 450(225 cases and 225 controls) were contacted and completed the study 2 refused and 4 were unavailable. Five factors associated with compliance were identified: high risk perception [Adjusted Odds Ratio(AOR) = 1.98, 95% Confidence Interval (CI), 1.32-2.95], one's family support [AOR = 1.86, 95% CI, 1.22-2.84], perceiving that the Community Drug Distributors (CDDs) are doing their work well [AOR = 2.84, 95% CI, 1.50-5.37] and perceiving measuring height is the best way to determine a person's treatment dose [AOR = 6.37, 95% CI, 2.10-19.29] are positive predictors of compliance to ivermectin.

Conclusion

Interventions to improve compliance in the area should focus on health education using epidemiological data in order to increase risk perception and dispelling misconceptions. Motivation and continued support to improve CDD's performance including training and incentives are crucial.

Immunisation with a multivalent, subunit vaccine reduces patent infection in a natural bovine model of onchocerciasis during intense field exposure

Human onchocerciasis, caused by the filarial nematode Onchocerca volvulus, is controlled almost exclusively by the drug ivermectin, which prevents pathology by targeting the microfilariae. However, this reliance on a single control tool has led to interest in vaccination as a potentially complementary strategy. Here, we describe the results of a trial in West Africa to evaluate a multivalent, subunit vaccine for onchocerciasis in the naturally evolved host-parasite relationship of Onchocerca ochengi in cattle. Naïve calves, reared in fly-proof accommodation, were immunised with eight recombinant antigens of O. ochengi, administered separately with either Freund's adjuvant or alum. The selected antigens were orthologues of O. volvulus recombinant proteins that had previously been shown to confer protection against filarial larvae in rodent models and, in some cases, were recognised by serum antibodies from putatively immune humans. The vaccine was highly immunogenic, eliciting a mixed IgG isotype response. Four weeks after the final immunisation, vaccinated and adjuvant-treated control calves were exposed to natural parasite transmission by the blackfly vectors in an area of Cameroon hyperendemic for O. ochengi. After 22 months, all the control animals had patent infections (i.e., microfilaridermia), compared with only 58% of vaccinated cattle (P = 0.015). This study indicates that vaccination to prevent patent infection may be an achievable goal in onchocerciasis, reducing both the pathology and transmissibility of the infection. The cattle model has also demonstrated its utility for preclinical vaccine discovery, although much research will be required to achieve the requisite target product profile of a clinical candidate.

River blindness, or onchocerciasis, is caused by a parasitic worm (Onchocerca volvulus) that is transmitted by blood-feeding blackflies, which breed in fast-flowing rivers. More than 37 million people are infected and may experience visual impairment and/or severe dermatitis. Control of onchocerciasis is largely dependent on a single drug, ivermectin. Whilst this is extremely effective at killing the worms' offspring (microfilariae) and preventing symptoms, ivermectin does not eliminate the long-lived adult parasites or always stop transmission. Consequently, treatments must be repeated for many years, and drug resistance may be emerging. Against this background, a vaccine against onchocerciasis would provide an important additional tool to sustain effective control. In this study, we evaluated eight worm antigens as vaccine components in cattle, which are often parasitized by O. ochengi (the closest relative of O. volvulus) in West Africa. Twelve uninfected animals received all eight antigens and were exposed to natural transmission of O. ochengi alongside 13 unvaccinated cattle. After almost two years, 92% of vaccinated animals had acquired adult worms, but only 58% were positive for microfilariae; whereas 100% of unvaccinated animals harboured both parasite stages. This suggests that a vaccine against microfilariae to prevent development of disease in humans may be achievable.

Mathematical modeling and the epidemiological research process

The authors of this paper advocate for the expanded use of mathematical models in epidemiology and provide an overview of the principles of mathematical modeling. Mathematical models can be used throughout the epidemiological research process. Initially they may help to refine study questions by visually expressing complex systems, directing literature searches, and identifying sensitive variables. In the study design phase, models can be used to test sampling strategies, to estimate sample size and power, and to predict outcomes for studies impractical due to time or ethical considerations. Once data are collected, models can assist in the interpretation of results, the exploration of causal pathways, and the combined analysis of data from multiple sources. Finally, models are commonly used in the process of applying research findings to public health practice by estimating population risk, predicting the effects of interventions, and contributing to the evaluation of ongoing programs. Mathematical modeling has the potential to make significant contributions to the field of epidemiology by enhancing the research process, serving as a tool for communicating findings to policymakers, and fostering interdisciplinary collaboration.

Feasibility of onchocerciasis elimination with ivermectin treatment in endemic foci in Africa: first evidence from studies in Mali and Senegal

Background

Mass treatment with ivermectin is a proven strategy for controlling onchocerciasis as a public health problem, but it is not known if it can also interrupt transmission and eliminate the parasite in endemic foci in Africa where vectors are highly efficient. A longitudinal study was undertaken in three hyperendemic foci in Mali and Senegal with 15 to 17 years of annual or six-monthly ivermectin treatment in order to assess residual levels of infection and transmission and test whether ivermectin treatment could be safely stopped in the study areas.

Methodology/Principal Findings

Skin snip surveys were undertaken in 126 villages, and 17,801 people were examined. The prevalence of microfilaridermia was <1% in all three foci. A total of 157,500 blackflies were collected and analyzed for the presence of Onchocerca volvulus larvae using a specific DNA probe, and vector infectivity rates were all below 0.5 infective flies per 1,000 flies. Except for a subsection of one focus, all infection and transmission indicators were below postulated thresholds for elimination. Treatment was therefore stopped in test areas of 5 to 8 villages in each focus. Evaluations 16 to 22 months after the last treatment in the test areas involved examination of 2,283 people using the skin snip method and a DEC patch test, and analysis of 123,000 black flies. No infected persons and no infected blackflies were detected in the test areas, and vector infectivity rates in other catching points were <0.2 infective flies per 1,000.

Conclusion/Significance

This study has provided the first empirical evidence that elimination of onchocerciasis with ivermectin treatment is feasible in some endemic foci in Africa. Although further studies are needed to determine to what extent these findings can be extrapolated to other endemic areas in Africa, the principle of elimination has been established. The African Programme for Onchocerciasis Control has adopted an additional objective to assess progress towards elimination endpoints in all onchocerciasis control projects and to guide countries on cessation of treatment where feasible.

The control of onchocerciasis, or river blindness, is based on annual or six-monthly ivermectin treatment of populations at risk. This has been effective in controlling the disease as a public health problem, but it is not known whether it can also eliminate infection and transmission to the extent that treatment can be safely stopped. Many doubt that this is feasible in Africa. A study was undertaken in three hyperendemic onchocerciasis foci in Mali and Senegal where treatment has been given for 15 to 17 years. The results showed that only few infections remained in the human population and that transmission levels were everywhere below postulated thresholds for elimination. Treatment was subsequently stopped in test areas in each focus, and follow-up evaluations did not detect any recrudescence of infection or transmission. Hence, the study has provided the first evidence that onchocerciasis elimination is feasible with ivermectin treatment in some endemic foci in Africa. Although further studies are needed to determine to what extent these findings can be extrapolated to other areas in Africa, the principle of onchocerciasis elimination with ivermectin treatment has been established.

The global programme to eliminate lymphatic filariasis: health impact after 8 years

BACKGROUND

In its first 8 years, the Global Programme to Eliminate Lymphatic Filariasis (GPELF) achieved an unprecedentedly rapid scale-up: >1.9 billion treatments with anti-filarial drugs (albendazole, ivermectin, and diethylcarbamazine) were provided via yearly mass drug administration (MDA) to a minimum of 570 million individuals living in 48 of the 83 initially identified LF-endemic countries.

METHODOLOGY

To assess the health impact that this massive global effort has had, we analyzed the benefits accrued first from preventing or stopping the progression of LF disease, and then from the broader anti-parasite effects ('beyond-LF' benefits) attributable to the use of albendazole and ivermectin. Projections were based on demographic and disease prevalence data from publications of the Population Reference Bureau, The World Bank, and the World Health Organization.

RESULT

Between 2000 and 2007, the GPELF prevented LF disease in an estimated 6.6 million newborns who would otherwise have acquired LF, thus averting in their lifetimes nearly 1.4 million cases of hydrocele, 800,000 cases of lymphedema and 4.4 million cases of subclinical disease. Similarly, 9.5 million individuals--previously infected but without overt manifestations of disease--were protected from developing hydrocele (6.0 million) or lymphedema (3.5 million). These LF-related benefits, by themselves, translate into 32 million DALYs (Disability Adjusted Life Years) averted. Ancillary, 'beyond-LF' benefits from the >1.9 billion treatments delivered by the GPELF were also enormous, especially because of the >310 million treatments to the children and women of childbearing age who received albendazole with/without ivermectin (effectively treating intestinal helminths, onchocerciasis, lice, scabies, and other conditions). These benefits can be described but remain difficult to quantify, largely because of the poorly defined epidemiology of these latter infections.

CONCLUSION

The GPELF has earlier been described as a 'best buy' in global health; this present tally of attributable health benefits from its first 8 years strengthens this notion considerably.

Efficacious, effective, and embedded interventions: implementation research in infectious disease control

Background

Research in infectious disease control is heavily skewed towards high end technology; development of new drugs, vaccines and clinical interventions. Oft ignored, is the evidence to inform the best strategies that ensure the embedding of interventions into health systems and amongst populations. In this paper we undertake an analysis of the challenge in the development of research for the sustainable implementation of disease control interventions.

Results

We highlight the fundamental differences between the research paradigms associated with the development of technologies and interventions for disease control on the one hand and the research paradigms required for enhancing the sustainable uptake of those very same interventions within the communities on the other. We provide a definition for implementation research in an attempt to underscore its critical role and explore the multidisciplinary science needed to address the challenges in disease control.

Conclusion

The greatest value for money in health research lies in the sustainable and effective implementation of already proven, efficacious solutions. The development of implementation research that can help provide some solutions on how this can be achieved is sorely needed.

After a decade of annual dose mass ivermectin treatment in Cameroon and Uganda, onchocerciasis transmission continues

OBJECTIVE

To evaluate the effectiveness of 10 years' annual single dose ivermectin treatment on onchocerciasis transmission in hyperendemic areas of Cameroon and Uganda.

METHODS

Baseline nodule and microfilaria ('skin snip') prevalence data were available from 10 hyperendemic sentinel communities in Cameroon (from 1996) and hyperendemic 20 sentinel communities in Uganda (from 1993). We returned to these villages in 2005, 10 months after the last annual ivermectin distribution, to repeat the cross-sectional surveys. Each sentinel community reported a mean interval treatment coverage of eligible persons of >88% (range 37-100%). Data were analyzed for more than 6200 person examinations. In Cameroon, 719 people >or=10 years were examined at the baseline survey in 1996 and 838 at the follow-up survey in 2005. In Uganda, 1590 people >or=10 years were examined at the baseline survey in 1993 and 2122 people at the follow-up survey in 2005. We also examined children under 10 in Cameroon (1996, n = 185; 2005, n = 448) and Uganda (1993, n = 177; 2005, n = 130). In Uganda, the vitality of worms was judged using standard histological criteria in 80 nodules excised in 2005.

RESULTS

The prevalence of microfilaria carriers among older children and adults (>or=10 years) in Cameroon sentinel communities dropped from 70.1% to 7.04% (P < 0.0001) over the 10-year treatment period; that of nodule carriers from 58% to 9.55% (P < 0.0001). Similarly, in Uganda, the prevalence of microfilaria carriers fell from 71.9% to 7.49% (P < 0.0001) over the 13-year treatment period, and that of nodule carriers from 53.21% to 9.66% (P < 0.0001). The number of microfilaria carriers among children <10 years in Cameroon decreased from 29.73% to 3.8% (P < 0.0001), and in Uganda from 33.89% to 3.1% (P < 0.0001). In 2005, worms excised from nodules in Uganda, 81.4% of males remained alive, and 64% of females, with 24% of them inseminated.

CONCLUSION

A decade or more of annual single dose ivermectin treatment in hyperendemic areas has reduced onchocerciasis to 'hypoendemicity', but onchocerciasis transmission persists. For now, annual treatment with ivermectin should be continued in formerly mesoendemic and hyperendemic zones.

Progress towards the elimination of onchocerciasis as a public-health problem in Uganda: opportunities, challenges and the way forward

The national onchocerciasis-control programme in Uganda successfully eliminated Simulium neavei s.s. from the Itwara focus in 1997, by monthly ground spraying with larvicidal temophos (Abate). Since then, no vectors have been caught in the main Itwara focus or two secondary foci in the same area. After 4 years of intervention, S. neavei s.s. has also been nearly eliminated from the Mpamba-Nkusi focus, and the elimination of this vector from two more foci (West Nile and Wambabya-Rwamarongo) appears quite feasible. There are, however, four isolated foci in Uganda (Budongo, Kashoya-Kitomi, Mount Elgon and Kigezi-Bwindi) which are probably too large and inaccessible to make the elimination of S. neavei s.s. by ground spraying a realistic possibility. Encouragingly, >70% of Ugandans have received an annual dose of ivermectin for at least 10 years, and the national programme of community-directed treatment with ivermectin (CDTI) is thought to be progressing towards sustainability. Despite the good treatment coverages, however, many potential vectors are still found infected with Onchocerca volvulus and many Ugandans have O. volvulus in their skin. There is now evidence that adult O. volvulus can be eliminated, within a period of about 6 years, through semiannual treatment with ivermectin. Together, the isolated foci where vector elimination is not considered feasible have a human population of about 700,000, most of whom (595,000) are eligible to receive ivermectin treatment. The estimated cost of each treatment, via the Ugandan CDTI, is U.S.$0.78 if the salaries of the government-employed personnel and the working time lost by the volunteers who act as community-directed drug distributors (CDD) are taken into account. If these 'expenses' are ignored, however, the cost falls to just U.S.$0.17/treatment, and the total costs for the four isolated foci where vector control is not likely to be successful become about U.S.$101,150/year for annual treatment (for an indefinite period of time) or approximately U.S.$202,300/year for semi-annual treatment (for the 6 years needed to eliminate adult O. volvulus), which would be the more cost-effective option. With the necessary financial support and the continued free supply of ivermectin from Merck, the national onchocerciasis-control programme could eliminate human onchocerciasis from Uganda, through a combination of semi-annual treatment with ivermectin in the isolated foci where S. neavei s.s. elimination is not feasible, and vector elimination in all the other foci.

Performance of predictors: evaluating sustainability in community-directed treatment projects of the African programme for onchocerciasis control

The predictors of sustainability of community-directed treatment with ivermectin (CDTI) at four implementation levels were evaluated in 41 African Programme for Onchocerciasis Control (APOC) projects, encompassing 492 communities in 10 countries. A model protocol provided information on indicators corresponding to nine aspects of a project that is likely to be sustainable at community level after the cessation of external support. Six of the nine aspects had components of community ownership as predictors of project sustainability. Quantitative and qualitative assessments were used to obtain individual community scores and an overall sustainability score for each project graded on a scale of 0-4. Of the 41 projects evaluated, 70% scored "satisfactorily" to "highly sustainable" at the community level. We found variations among countries and that health system weaknesses could hamper community efforts in sustaining a project, such as when ivermectin was delivered late. Community ownership was of primary importance to the community score, and the community-level scores correlated with overall project sustainability. The therapeutic coverage achieved in each project correlated with the ratio of volunteer ivermectin distributors per population served. Surprisingly, the performance of these distributors was not affected by the direct incentives offered, and coverage appeared to be highest when cash or in-kind compensation was not given at all. Although further research is required, anecdotal evidence pointed to diverse indirect benefits for distributors-political goodwill, personal satisfaction and altruistic fulfillment. The results demonstrate that community ownership is among the important determining factors of sustainability of community-based programmes.

River blindness: a success story under threat?

The success of the Onchocerciasis Control Programme is undeniable and exemplary, say the authors, but it is too early to claim victory against river blindness.

Global socioeconomic impact of cystic echinococcosis

Because the human and economic losses of cystic echinococcosis are substantial, global prevention and control measures should be increased.

Cystic echinococcosis (CE) is an emerging zoonotic parasitic disease throughout the world. Human incidence and livestock prevalence data of CE were gathered from published literature and the Office International des Epizooties databases. Disability-adjusted life years (DALYs) and monetary losses, resulting from human and livestock CE, were calculated from recorded human and livestock cases. Alternative values, assuming substantial underreporting, are also reported. When no underreporting is assumed, the estimated human burden of disease is 285,407 (95% confidence interval [CI], 218,515–366,133) DALYs or an annual loss of US $193,529,740 (95% CI, $171,567,331–$217,773,513). When underreporting is accounted for, this amount rises to 1,009,662 (95% CI, 862,119–1,175,654) DALYs or US $763,980,979 (95% CI, $676,048,731–$857,982,275). An annual livestock production loss of at least US $141,605,195 (95% CI, $101,011,553–$183,422,465) and possibly up to US $2,190,132,464 (95% CI, $1,572,373,055–$2,951,409,989) is also estimated. This initial valuation demonstrates the necessity for increased monitoring and global control of CE.

Ecologists can enable communities to implement malaria vector control in Africa

BACKGROUND

Integrated vector management (IVM) for malaria control requires ecological skills that are very scarce and rarely applied in Africa today. Partnerships between communities and academic ecologists can address this capacity deficit, modernize the evidence base for such approaches and enable future scale up.

METHODS

Community-based IVM programmes were initiated in two contrasting settings. On Rusinga Island, Western Kenya, community outreach to a marginalized rural community was achieved by University of Nairobi through a community-based organization. In Dar es Salaam, Tanzania, Ilala Municipality established an IVM programme at grassroots level, which was subsequently upgraded and expanded into a pilot scale Urban Malaria Control Programme with support from national academic institutes.

RESULTS

Both programmes now access relevant expertise, funding and policy makers while the academic partners benefit from direct experience of community-based implementation and operational research opportunities. The communities now access up-to-date malaria-related knowledge and skills for translation into local action. Similarly, the academic partners have acquired better understanding of community needs and how to address them.

CONCLUSION

Until sufficient evidence is provided, community-based IVM remains an operational research activity. Researchers can never directly support every community in Africa so community-based IVM strategies and tactics will need to be incorporated into undergraduate teaching programmes to generate sufficient numbers of practitioners for national scale programmes. Academic ecologists at African institutions are uniquely positioned to enable the application of practical environmental and entomological skills for malaria control by communities at grassroots level and should be supported to fulfil this neglected role.

Ecologists can enable communities to implement malaria vector control in Africa

BACKGROUND

Integrated vector management (IVM) for malaria control requires ecological skills that are very scarce and rarely applied in Africa today. Partnerships between communities and academic ecologists can address this capacity deficit, modernize the evidence base for such approaches and enable future scale up.

METHODS

Community-based IVM programmes were initiated in two contrasting settings. On Rusinga Island, Western Kenya, community outreach to a marginalized rural community was achieved by University of Nairobi through a community-based organization. In Dar es Salaam, Tanzania, Ilala Municipality established an IVM programme at grassroots level, which was subsequently upgraded and expanded into a pilot scale Urban Malaria Control Programme with support from national academic institutes.

RESULTS

Both programmes now access relevant expertise, funding and policy makers while the academic partners benefit from direct experience of community-based implementation and operational research opportunities. The communities now access up-to-date malaria-related knowledge and skills for translation into local action. Similarly, the academic partners have acquired better understanding of community needs and how to address them.

CONCLUSION

Until sufficient evidence is provided, community-based IVM remains an operational research activity. Researchers can never directly support every community in Africa so community-based IVM strategies and tactics will need to be incorporated into undergraduate teaching programmes to generate sufficient numbers of practitioners for national scale programmes. Academic ecologists at African institutions are uniquely positioned to enable the application of practical environmental and entomological skills for malaria control by communities at grassroots level and should be supported to fulfil this neglected role.

Chemistry-to-gene screens in Caenorhabditis elegans

The nematode worm Caenorhabditis elegans is a genetic model organism linked to an impressive portfolio of fundamental discoveries in biology. This free-living nematode, which can be easily and inexpensively grown in the laboratory, is also a natural vehicle for screening for drugs that are active against nematode parasites. Here, we show that chemistry-to-gene screens using this animal model can define targets of antiparasitic drugs, identify novel candidate drug targets and contribute to the discovery of new drugs for treating human diseases.

Research on infectious diseases requires better coordination

This special supplement of Nature Medicine, directed at the topic of emerging infectious diseases, is very timely. Recent high-profile outbreaks have highlighted the global risk that infectious agents, both new and old, represent for society. The experience of severe acute respiratory syndrome (SARS) shows the risk posed by emerging infectious diseases, but also the power of strongly coordinated global surveillance and public health measures, coupled with scientific research, to keep infection under control^1,2. Diseases such as drug-resistant malaria continue to be threats. There is a need to enhance global resources to investigate, detect and respond to emerging infections, and to appropriately coordinate and direct research efforts to meet the challenges presented by these diseases.

Additional health and development activities for community-directed distributors of ivermectin: threat or opportunity for onchocerciasis control?

We studied the involvement of community-directed distributors (CDDs) of ivermectin for onchocerciasis control in other health and development activities in Nigeria, Togo and Cameroon. Most CDDs (82%) were involved in additional activities, especially EPI, water and sanitation and community development projects. These activities did not take up much time and were not considered an important burden. Ivermectin treatment coverage did not decline with increasing number of additional activities. Other health programmes are interested in building on the experiences and structures of community-directed treatment with ivermectin and involving CDDs in their health programmes. Some, such as EPI, provide financial incentives. Incentives by other programmes may enhance the performance of CDDs when they are selected on the basis of their CDD status. CDDs, health personnel and community members have very positive attitudes towards greater involvement of CDDs in additional health and development activities. We conclude that additional activities for CDDs do not pose a threat to but rather provide an opportunity to strengthen sustainability and effectiveness of ivermectin treatment.