Satellite mapping of Loa loa prevalence in relation to ivermectin use in west and central Africa

A call for loiasis to be added to the WHO list of neglected tropical diseases

Loiasis, also called African eye worm, is not currently on WHO's list of priority neglected tropical diseases, even though the risk that individuals with high Loa loa microfilarial densities will develop potentially fatal encephalopathy when they take ivermectin has complicated efforts to use mass drug administration for onchocerciasis (river blindness) and lymphatic filariasis control in co-endemic areas. At least 10 million residents of central and west Africa are thought to have loiasis, which causes painful and itchy subcutaneous oedema, arthralgia, and discomfort when adult helminths that are 3-7 cm in length are present under the conjunctiva of the eye. High levels of microfilaraemia are associated with renal, cardiac, neurological, and other sequelae, and an increased risk of death. The public health burden of loiasis could be greatly reduced with expanded use of diagnostic tests, anthelmintic treatment, and control of the Chrysops spp (tabanid flies) vectors that transmit the parasite. Loiasis should be added to the next revision of the WHO neglected tropical disease priority list, not merely because its inclusion will support the elimination of other skin and subcutaneous neglected tropical diseases, but also because of the complications caused by loiasis itself.

Environmental Factors Associated With Loa loa Microfilaria Prevalence and Intensity in Diverse Bioecological Zones of Cameroon

Loiasis (African Eye Worm) is a filarial infection caused by Loa loa and transmitted by Chrysops vectors, which are confined to the tropical rainforests of Central and West Africa. Loiasis is a major impediment to control and elimination programmes that use the drug ivermectin due to the risk of serious adverse events. There is an urgent need to better refine and map high-risk communities. This study aimed to quantify and predict environmental factors associated with loiasis across five bioecological zones in Cameroon. The L. loa microfilaria (mf) prevalence (%) and intensity (mf number/ml) data from 42 villages within an Equatorial Rainforest and Savannah region were examined in relation to climate, topographic and forest-related data derived from satellite remote sensing sources. Differences between zones and regions were examined using nonparametric tests, and the relationship between L. loa mf prevalence, mf intensity, and the environmental factors using polynomial regression models. Overall, the L. loa mf prevalence was 11.6%, L. loa intensity 927.4 mf/ml, mean annual temperature 23.7°C, annual precipitation 2143.2 mm, elevation 790 m, tree canopy cover 46.7%, and canopy height 19.3m. Significant differences between the Equatorial Rainforest and Savannah region were found. Within the Equatorial Rainforest region, no significant differences were found. However, within the Savannah region, significant differences between the three bioecological zones were found, and the regression models indicated that tree canopy cover and elevation were significant predictors, explaining 85.1% of the L. loa mf prevalence (adjusted R2 = 0.851; p<0.001) and tree cover alone was significant, explaining 58.1% of the mf intensity (adjusted R2 = 0.581; p<0.001). The study highlights that environmental analysis can help delineate risk at different geographical scales, which may be practical for developing larger scale operational plans for mapping and implementing safe effective interventions.

Projected Number of People With Onchocerciasis-Loiasis Coinfection in Africa, 1995 to 2025

BACKGROUND

Onchocerciasis elimination through mass drug administration (MDA) is hampered by coendemicity of Loa loa, as people with high L. loa microfilariae (mf) density can develop serious adverse events (SAEs) after ivermectin treatment. We assessed the geographical overlap of onchocerciasis and loiasis prevalence and estimated the number of coinfected individuals at risk of post-ivermectin SAEs in West and Central Africa from 1995 to 2025.

METHODS

Focusing on regions with suspected loiasis transmission in 14 countries, we overlaid precontrol maps of loiasis and onchocerciasis prevalence to calculate precontrol prevalence of coinfection by 5 km2 × 5 km2 pixel, distinguishing different categories of L. loa mf intensity. Using statistical and mathematical models, we predicted prevalence of both infections and coinfection for 2015 and 2025, accounting for the impact of MDA with ivermectin.

RESULTS

The number of people infected with onchocerciasis was predicted to decline from almost 19 million in 1995 to 4 million in 2025. Of these, 137 000 people were estimated to also have L. loa hypermicrofilaremia (≥20 000 L. loa mf/mL) in 1995, declining to 31 000 in 2025. In 2025, 92.8% of coinfected cases with loiasis hypermicrofilaremia are predicted to live in hypoendemic areas currently not targeted for MDA.

CONCLUSIONS

Loiasis coinfection is a major concern for onchocerciasis elimination in Africa. We predict that under current strategies, at least 31 000 coinfected people still require treatment for onchocerciasis in 2025 while being at risk of SAEs, justifying continued efforts in research and development for safer drugs and control strategies.

Environmental factors associated with the distribution of Loa loa vectors Chrysops spp. in Central and West Africa: seeing the forest for the trees

BACKGROUND

Loiasis is caused by the filarial parasite Loa loa, which is widespread through Central and West Africa and largely confined the tropical equatorial rainforests. The tabanid flies Chrysops silacea and Chrysops dimidiata are the main vectors driving transmission. This study aimed to better define the spatial distribution and ecological niche of the two vectors to help define spatial-temporal risk and target appropriate, timely intervention strategies for filariasis control and elimination programmes.

METHODS

Chrysops spp. distributions were determined by collating information from the published literature into a database, detailing the year, country, locality, latitude/longitude and species collected. Environmental factors including climate, elevation and tree canopy characteristics were summarised for each vector from data obtained from satellite modelled data or imagery, which were also used to identify areas with overt landcover changes. The presence of each Chrysops vector was predicted using a maximum entropy species distribution modelling (MaxEnt) method.

RESULTS

A total of 313 location-specific data points from 59 published articles were identified across seven loiasis endemic countries. Of these, 186 sites were included in the climate and elevation analysis, and due to overt landcover changes, 83 sites included in tree canopy analysis and MaxEnt model. Overall, C. silacea and C. dimidiata were found to have similar ranges; annual mean temperature (24.6 °C and 24.1 °C, respectively), annual precipitation (1848.6 mm and 1868.8 mm), elevation (368.8 m and 400.6 m), tree canopy cover (61.4% and 66.9%) and tree canopy height (22.4 m and 25.1 m). MaxEnt models found tree canopy coverage was a significant environmental variable for both vectors.

CONCLUSIONS

The Chrysops spp. database and large-scale environmental analysis provides insights into the spatial and ecological parameters of the L. loa vectors driving transmission. These may be used to further delineate loiasis risk, which will be important for implementing filariasis control and elimination programmes in the equatorial rainforest region of Central and West Africa.

The changing global landscape of health and disease: addressing challenges and opportunities for sustaining progress towards control and elimination of neglected tropical diseases (NTDs)

The drive to control neglected tropical diseases (NTDs) has had many successes but to reach defined targets new approaches are required. Over the last decade, NTD control programmes have benefitted from increased resources, and from effective partnerships and long-term pharmaceutical donations. Although the NTD agenda is broader than those diseases of parasitic aetiology there has been a massive up-scaling of the delivery of medicines to some billion people annually. Recipients are often the poorest, with the aspiration that NTD programmes are key to universal health coverage as reflected within the 2030 United Nations sustainable development goals (SDGs). To reach elimination targets, the community will need to adapt global events and changing policy environments to ensure programmes are responsive and can sustain progress towards NTD targets. Innovative thinking embedded within regional and national health systems is needed. Policy makers, managers and frontline health workers are the mediators between challenge and change at global and local levels. This paper attempts to address the challenges to end the chronic pandemic of NTDs and achieve the SDG targets. It concludes with a conceptual framework that illustrates the interactions between these key challenges and opportunities and emphasizes the health system as a critical mediator.

Identifying co-endemic areas for major filarial infections in sub-Saharan Africa: seeking synergies and preventing severe adverse events during mass drug administration campaigns

Background

Onchocerciasis and lymphatic filariasis (LF) are major filarial infections targeted for elimination in most endemic sub-Saharan Africa (SSA) countries by 2020/2025. The current control strategies are built upon community-directed mass administration of ivermectin (CDTI) for onchocerciasis, and ivermectin plus albendazole for LF, with evidence pointing towards the potential for novel drug regimens. When distributing microfilaricides however, considerable care is needed to minimise the risk of severe adverse events (SAEs) in areas that are co-endemic for onchocerciasis or LF and loiasis. This work aims to combine previously published predictive risk maps for onchocerciasis, LF and loiasis to (i) explore the scale of spatial heterogeneity in co-distributions, (ii) delineate target populations for different treatment strategies, and (iii) quantify populations at risk of SAEs across the continent.

Methods

Geographical co-endemicity of filarial infections prior to the implementation of large-scale mass treatment interventions was analysed by combining a contemporary LF endemicity map with predictive prevalence maps of onchocerciasis and loiasis. Potential treatment strategies were geographically delineated according to the level of co-endemicity and estimated transmission intensity.

Results

In total, an estimated 251 million people live in areas of LF and/or onchocerciasis transmission in SSA, based on 2015 population estimates. Of these, 96 million live in areas co-endemic for both LF and onchocerciasis, providing opportunities for integrated control programmes, and 83 million live in LF-monoendemic areas potentially targetable for the novel ivermectin-diethylcarbamazine-albendazole (IDA) triple therapy. Only 4% of the at-risk population live in areas co-endemic with high loiasis transmission, representing up to 1.2 million individuals at high risk of experiencing SAEs if treated with ivermectin. In these areas, alternative treatment strategies should be explored, including biannual albendazole monotherapy for LF (1.4 million individuals) and ‘test-and-treat’ strategies (8.7 million individuals) for onchocerciasis.

Conclusions

These maps are intended to initiate discussion around the potential for tailored treatment strategies, and highlight populations at risk of SAEs. Further work is required to test and refine strategies in programmatic settings, providing the empirical evidence needed to guide efforts towards the 2020/2025 goals and beyond.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2655-5) contains supplementary material, which is available to authorized users.

Loa loa vectors Chrysops spp.: perspectives on research, distribution, bionomics, and implications for elimination of lymphatic filariasis and onchocerciasis

BACKGROUND

Loiasis is a filarial disease caused Loa loa. The main vectors are Chrysops silacea and C. dimidiata which are confined to the tropical rainforests of Central and West Africa. Loiasis is a mild disease, but individuals with high microfilaria loads may suffer from severe adverse events if treated with ivermectin during mass drug administration campaigns for the elimination of lymphatic filariasis and onchocerciasis. This poses significant challenges for elimination programmes and alternative interventions are required in L. loa co-endemic areas. The control of Chrysops has not been considered as a viable cost-effective intervention; we reviewed the current knowledge of Chrysops vectors to assess the potential for control as well as identified areas for future research.

RESULTS

We identified 89 primary published documents on the two main L. loa vectors C. silacea and C dimidiata. These were collated into a database summarising the publication, field and laboratory procedures, species distributions, ecology, habitats and methods of vector control. The majority of articles were from the 1950-1960s. Field studies conducted in Cameroon, Democratic Republic of Congo, Equatorial Guinea, Nigeria and Sudan highlighted that C. silacea is the most important and widespread vector. This species breeds in muddy streams or swampy areas of forests or plantations, descends from forest canopies to feed on humans during the day, is more readily adapted to human dwellings and attracted to wood fires. Main vector targeted measures proposed to impact on L. loa transmission included personal repellents, household screening, indoor residual spraying, community-based environmental management, adulticiding and larviciding.

CONCLUSIONS

This is the first comprehensive review of the major L. loa vectors for several decades. It highlights key vector transmission characteristics that may be targeted for vector control providing insights into the potential for integrated vector management, with multiple diseases being targeted simultaneously, with shared human and financial resources and multiple impact. Integrated vector management programmes for filarial infections, especially in low transmission areas of onchocerciasis, require innovative approaches and alternative strategies if the elimination targets established by the World Health Organization are to be achieved.

Model-Based Geostatistical Mapping of the Prevalence of Onchocerca volvulus in West Africa

BACKGROUND

The initial endemicity (pre-control prevalence) of onchocerciasis has been shown to be an important determinant of the feasibility of elimination by mass ivermectin distribution. We present the first geostatistical map of microfilarial prevalence in the former Onchocerciasis Control Programme in West Africa (OCP) before commencement of antivectorial and antiparasitic interventions.

METHODS AND FINDINGS

Pre-control microfilarial prevalence data from 737 villages across the 11 constituent countries in the OCP epidemiological database were used as ground-truth data. These 737 data points, plus a set of statistically selected environmental covariates, were used in a Bayesian model-based geostatistical (B-MBG) approach to generate a continuous surface (at pixel resolution of 5 km x 5km) of microfilarial prevalence in West Africa prior to the commencement of the OCP. Uncertainty in model predictions was measured using a suite of validation statistics, performed on bootstrap samples of held-out validation data. The mean Pearson's correlation between observed and estimated prevalence at validation locations was 0.693; the mean prediction error (average difference between observed and estimated values) was 0.77%, and the mean absolute prediction error (average magnitude of difference between observed and estimated values) was 12.2%. Within OCP boundaries, 17.8 million people were deemed to have been at risk, 7.55 million to have been infected, and mean microfilarial prevalence to have been 45% (range: 2-90%) in 1975.

CONCLUSIONS AND SIGNIFICANCE

This is the first map of initial onchocerciasis prevalence in West Africa using B-MBG. Important environmental predictors of infection prevalence were identified and used in a model out-performing those without spatial random effects or environmental covariates. Results may be compared with recent epidemiological mapping efforts to find areas of persisting transmission. These methods may be extended to areas where data are sparse, and may be used to help inform the feasibility of elimination with current and novel tools.

Hypo-endemic onchocerciasis hotspots: defining areas of high risk through micro-mapping and environmental delineation

Background

Onchocerciasis (river blindness) caused by the parasite Onchocercavolvulus and transmitted by riverine Simulium spp. (Black flies) is targeted for elimination in Africa. This is a significant change in strategy from the ‘control’ of meso- and hyper-endemic areas through mass drug administration (MDA) with Mectizan® (ivermectin), to the ‘elimination’ in all endemic areas where a range of interventions may be required. The most significant challenges of elimination in low transmission or hypo-endemic areas are two-fold. First, there are vast remote areas where the focality of low transmission is relatively undefined. Second, the treatment with ivermectin increases the risk of serious adverse events (SAEs) in individuals with high parasitaemias of Loa loa, a filarial parasite widespread in Central and West Africa, which causes Tropical eye worm and transmitted by Chrysops spp. (Deer flies).

Discussion

We therefore propose novel mapping approaches using remote sensing satellite and modelled environmental data to be used in combination with rapid field surveys to help resolve the problems of targeting the expansion of onchocerciasis elimination activities in L. loa co-endemic areas. First, we demonstrate that micro-stratification overlap mapping (MOM) of available onchocerciasis and loiasis prevalence maps can be used to identify 12 key high risk areas, where low O. volvulusand high L. loa transmission overlap, which we define as “hypo-endemic hotspots”. Second we show that integrated micro-mapping of prevalence data, and the use of environmental data to delineate riverine and forest risk factors associated with Simulium spp. and Chrysops spp. vector habitats can further help to define target intervention areas i.e. secondary hotspots within hotspots, to help avoid the risk of SAEs.

Summary

These mapping examples demonstrate the value of bringing prevalence, entomological and ecological information together to develop maps for planned implementation and targeted strategies. This is critical as better mapping may the reduce costs and lower the L. loa associated risks, especially if there are extensive areas of low endemicity that may require treatment with ivermectin or alternative strategies. Novel cost-effective approaches are necessary if elimination of O.volvulus transmission in Africa is to be achieved in an efficient and safe way by the goal of 2025.

Electronic supplementary material

The online version of this article (doi:10.1186/s40249-015-0069-6) contains supplementary material, which is available to authorized users.

Human Onchocerciasis: Modelling the Potential Long-term Consequences of a Vaccination Programme

Background

Currently, the predominant onchocerciasis control strategy in Africa is annual mass drug administration (MDA) with ivermectin. However, there is a consensus among the global health community, supported by mathematical modelling, that onchocerciasis in Africa will not be eliminated within proposed time frameworks in all endemic foci with only annual MDA, and novel and alternative strategies are urgently needed. Furthermore, use of MDA with ivermectin is already compromised in large areas of central Africa co-endemic with Loa loa, and there are areas where suboptimal or atypical responses to ivermectin have been documented. An onchocerciasis vaccine would be highly advantageous in these areas.

Methodology/Principal Findings

We used a previously developed onchocerciasis transmission model (EPIONCHO) to investigate the impact of vaccination in areas where loiasis and onchocerciasis are co-endemic and ivermectin is contraindicated. We also explore the potential influence of a vaccination programme on infection resurgence in areas where local elimination has been successfully achieved. Based on the age range included in the Expanded Programme on Immunization (EPI), the vaccine was assumed to target 1 to 5 year olds. Our modelling results indicate that the deployment of an onchocerciasis vaccine would have a beneficial impact in onchocerciasis–loiasis co-endemic areas, markedly reducing microfilarial load in the young (under 20 yr) age groups.

Conclusions/Significance

An onchocerciasis prophylactic vaccine would reduce the onchocerciasis disease burden in populations where ivermectin cannot be administered safely. Moreover, a vaccine could substantially decrease the chance of re-emergence of Onchocerca volvulus infection in areas where it is deemed that MDA with ivermectin can be stopped. Therefore, a vaccine would protect the substantial investments made by present and past onchocerciasis control programmes, decreasing the chance of disease recrudescence and offering an important additional tool to mitigate the potentially devastating impact of emerging ivermectin resistance.

Novel and alternative strategies are required to meet the demanding control and elimination (of infection) goals for human onchocerciasis (river blindness) in Africa. Due to the overlapping distribution of onchocerciasis and loiasis (African eye worm) in forested areas of central Africa, millions of people living in such areas are not well served by current interventions because they cannot safely receive the antiparasitic drug ivermectin that is distributed en masse to treat onchocerciasis elsewhere in Africa. The Onchocerciasis Vaccine for Africa—TOVA—Initiative has been established to develop and trial an onchocerciasis vaccine. We model the potential impact of a hypothetical childhood vaccination programme rolled out in areas where co-endemicity of onchocerciasis and African eye worm makes mass distribution of ivermectin difficult and potentially unsafe for treating, controlling and eliminating river blindness. We find that, 15 years into the programme, a vaccine would substantially reduce infection levels in children and young adults, protecting them from the morbidity and mortality associated with onchocerciasis. Most benefit would be reaped from a long-lived vaccine, even if only partially protective. We also discuss how a vaccine could substantially reduce the risk of re-emergence of onchocerciasis in areas freed from infection after years of successful intervention.

Landscape influence on spatial patterns of meningeal worm and liver fluke infection in white-tailed deer

Parasites that primarily infect white-tailed deer (Odocoileus virginianus), such as liver flukes (Fascioloides magna) and meningeal worm (Parelaphostrongylus tenuis), can cause morbidity and mortality when incidentally infecting moose (Alces alces). Ecological factors are expected to influence spatial variation in infection risk by affecting the survival of free-living life stages outside the host and the abundance of intermediate gastropod hosts. Here, we investigate how ecology influenced the fine-scale distribution of these parasites in deer in Voyageurs National Park, Minnesota. Deer pellet groups (N = 295) were sampled for the presence of P. tenuis larvae and F. magna eggs. We found that deer were significantly more likely to be infected with P. tenuis in habitats with less upland deciduous forest and more upland mixed conifer forest and shrub, a pattern that mirrored microhabitat differences in gastropod abundances. Deer were also more likely to be infected with F. magna in areas with more marshland, specifically rooted-floating aquatic marshes (RFAMs). The environment played a larger role than deer density in determining spatial patterns of infection for both parasites, highlighting the importance of considering ecological factors on all stages of a parasite's life cycle in order to understand its occurrence within the definitive host.

Neglected tropical diseases: now more than just 'other diseases'--the post-2015 agenda

Neglected tropical diseases (NTDs) have become recognised as important health problems facing at least a billion people in the low-income countries and the poorest communities in middle-income countries. WHO plays a leading role in developing strategies to address these diseases, pharmaceutical companies provide drug donations to treat or control the NTDs and many partners from different constituencies have become increasingly committed to their control or elimination. This review looks to the post-2015 agenda and emphasises that despite the progress made over recent years, if the targets established are to be achieved, then not only will additional financial resources be required to up-scale treatments and increase access, but increased applied and operational research will be necessary to address problems and human capacity in NTD skills will need to be strengthened. Continuing advocacy for the relevance of control or elimination of NTDs must be placed in the context of universal health coverage and access to donated essential medicines for the poor as a right. The evidence that investment in NTD interventions are cost-effective and impact not only on health, but also to enhance socio-economic development, must be refined and promulgated. The global burden of disease attributable to NTDs requires reassessment to appropriately define the true burden, while the potential for unexpected events, political, climatic, environmental as well as biological, have the potential to reduce future progress towards the agreed post-2015 targets. NTD progress towards the WHO Roadmap targets and the fulfilment of the World Health Assembly Resolution 66.12 of 2013 demand continued commitment from all partner constituencies when challenges emerge.

A research agenda for helminth diseases of humans: diagnostics for control and elimination programmes

Diagnostic tools appropriate for undertaking interventions to control helminth infections are key to their success. Many diagnostic tests for helminth infection have unsatisfactory performance characteristics and are not well suited for use in the parasite control programmes that are being increasingly implemented. Although the application of modern laboratory research techniques to improve diagnostics for helminth infection has resulted in some technical advances, uptake has not been uniform. Frequently, pilot or proof of concept studies of promising diagnostic technologies have not been followed by much needed product development, and in many settings diagnosis continues to rely on insensitive and unsatisfactory parasitological or serodiagnostic techniques. In contrast, PCR-based xenomonitoring of arthropod vectors, and use of parasite recombinant proteins as reagents for serodiagnostic tests, have resulted in critical advances in the control of specific helminth parasites. The Disease Reference Group on Helminths Infections (DRG4), established in 2009 by the Special Programme for Research and Training in Tropical Diseases (TDR) was given the mandate to review helminthiases research and identify research priorities and gaps. In this review, the diagnostic technologies relevant to control of helminth infections, either available or in development, are reviewed. Critical gaps are identified and opportunities to improve needed technologies are discussed.

Neglected tropical diseases and the millennium development goals: why the "other diseases" matter: reality versus rhetoric

Since 2004 there has been an increased recognition of the importance of Neglected Tropical Diseases (NTDs) as impediments to development. These diseases are caused by a variety of infectious agents - viruses, bacteria and parasites - which cause a diversity of clinical conditions throughout the tropics. The World Health Organisation (WHO) has defined seventeen of these conditions as core NTDs. The objectives for the control, elimination or eradication of these conditions have been defined in World Health Assembly resolutions whilst the strategies for the control or elimination of individual diseases have been defined in various WHO documents. Since 2005 there has been a drive for the expanded control of these diseases through an integrated approach of mass drug administration referred to as Preventive Chemotherapy via community-based distribution systems and through schools. This has been made possible by donations from major pharmaceutical companies of quality and efficacious drugs which have a proven track record of safety. As a result of the increased commitment of endemic countries, bilateral donors and non-governmental development organisations, there has been a considerable expansion of mass drug administration. In particular, programmes targeting lymphatic filariasis, onchocerciasis, schistosomiasis, trachoma and soil transmitted helminth infections have expanded to treat 887. 8 million people in 2009. There has been significant progress towards guinea worm eradication, and the control of leprosy and human African trypanosomiasis. This paper responds to what the authors believe are inappropriate criticisms of these programmes and counters accusations of the motives of partners made in recently published papers. We provide a detailed response and update the information on the numbers of global treatments undertaken for NTDs and list the success stories to date.The paper acknowledges that in undertaking any health programme in environments such as post-conflict countries, there are always challenges. It is also recognised that NTD control must always be undertaken within the health system context. However, it is important to emphasise that the availability of donated drugs, the multiple impact of those drugs, the willingness of countries to undertake their distribution, thereby committing their own resources to the programmes, and the proven beneficial results outweigh the problems which are faced in environments where communities are often beyond the reach of health services. Given the availability of these interventions, their cost effectiveness and the broader development impact we believe it would be unethical not to continue programmes of such long term benefit to the "bottom billion".

Integrated rapid mapping of onchocerciasis and loiasis in the Democratic Republic of Congo: impact on control strategies

BACKGROUND

Onchocerciasis can be effectively controlled by annual mass treatment with ivermectin in endemic communities. However, in communities that are endemic for loiasis there may be significant risk of severe adverse reactions after ivermectin treatment. Planning of control requires therefore mapping of these two infections using rapid assessment tools developed for each disease. These tools were initially implemented independently till the feasibility of combining them was demonstrated. This paper reports the results of integrated mapping in four epidemiological zones in the Democratic Republic of Congo and its implications on operational decision-making on ivermectin treatment.

METHODS

Rapid assessment surveys were conducted between 2004 and 2005 using both rapid epidemiological mapping of onchocerciasis (REMO) and rapid assessment procedure for loiasis (RAPLOA). The survey results were subjected to a spatial analysis in order to generate for each of the two diseases maps of the estimated prevalence of infection throughout the four zones.

RESULTS

Surveys were undertaken in 788 villages where 25,754 males were examined for palpable onchocercal nodules and 62,407 people were interviewed for history of eye worm. The results showed major differences in the geographic distribution of the two diseases. Loiasis was highly endemic in some areas, where special precautions were required, but not in others where routine ivermectin treatment could proceed.

CONCLUSION

Integrated rapid mapping of onchocerciasis and loiasis reduces both time and cost of surveys and greatly facilitates operational decision-making on ivermectin treatment in areas where loiasis might be co-endemic.

The geographic distribution of Loa loa in Africa: results of large-scale implementation of the Rapid Assessment Procedure for Loiasis (RAPLOA)

Background

Loiasis is a major obstacle to ivermectin treatment for onchocerciasis control and lymphatic filariasis elimination in central Africa. In communities with a high level of loiasis endemicity, there is a significant risk of severe adverse reactions to ivermectin treatment. Information on the geographic distribution of loiasis in Africa is urgently needed but available information is limited. The African Programme for Onchocerciasis Control (APOC) undertook large scale mapping of loiasis in 11 potentially endemic countries using a rapid assessment procedure for loiasis (RAPLOA) that uses a simple questionnaire on the history of eye worm.

Methodology/Principal Findings

RAPLOA surveys were done in a spatial sample of 4798 villages covering an area of 2500×3000 km centred on the heartland of loiasis in Africa. The surveys showed high risk levels of loiasis in 10 countries where an estimated 14.4 million people live in high risk areas. There was a strong spatial correlation among RAPLOA data, and kriging was used to produce spatially smoothed contour maps of the interpolated prevalence of eye worm and the predictive probability that the prevalence exceeds 40%.

Conclusion/Significance

The contour map of eye worm prevalence provides the first global map of loiasis based on actual survey data. It shows a clear distribution with two zones of hyper endemicity, large areas that are free of loiasis and several borderline or intermediate zones. The surveys detected several previously unknown hyperendemic foci, clarified the distribution of loiasis in the Central African Republic and large parts of the Republic of Congo and the Democratic Republic of Congo for which hardly any information was available, and confirmed known loiasis foci. The new maps of the prevalence of eye worm and the probability that the prevalence exceeds the risk threshold of 40% provide critical information for ivermectin treatment programs among millions of people in Africa.

Loiasis is a neglected tropical disease caused by infection with the filarial parasite Loa loa, transmitted by Chrysops vectors. Loiasis has recently emerged as a disease of public health importance when neurologic serious adverse events (SAEs) were reported in individuals with high L. loa microfilaraemia after ivermectin treatment. This had a negative impact on the control of onchocerciasis and lymphatic filariasis in areas of co-endemicity with loiasis. Microfilarial prevalence of 20% has been suggested as the threshold above which there is an unacceptable risk of SAEs with ivermectin treatment.The African Programme for Onchocerciasis Control (APOC) undertook large scale mapping of loiasis in 11 potentially endemic countries using a rapid assessment procedure for loiasis (RAPLOA) that uses a simple questionnaire on the history of eye worm. A geostatistical analysis method called kriging applied to the results in 4798 sampled villages generated a contour map of eye worm prevalence, providing the first global map of loiasis based on actual survey data. This map showed high risk levels of loiasis in 10 countries where an estimated 14.4 million people live in high risk areas.

Mapping, monitoring, and surveillance of neglected tropical diseases: towards a policy framework

As national programmes respond to the new opportunities presented for scaling up preventive chemotherapy programmes for the coadministration of drugs to target lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminthiasis, and trachoma, possible synergies between existing disease-specific policies and protocols need to be examined. In this report we compare present policies for mapping, monitoring, and surveillance for these diseases, drawing attention to both the challenges and opportunities for integration. Although full integration of all elements of mapping, monitoring, and surveillance strategies might not be feasible for the diseases targeted through the preventive chemotherapy approach, there are opportunities for integration, and we present examples of integrated strategies. Finally, if advantage is to be taken of scaled up interventions to address neglected tropical diseases, efforts to develop rapid, inexpensive, and easy-to-use methods, whether disease-specific or integrated, should be increased. We present a framework for development of an integrated monitoring and evaluation system that combines both integrated and disease-specific strategies.

Global epidemiology, ecology and control of soil-transmitted helminth infections

Soil-transmitted helminth (STH) infections are among the most prevalent of chronic human infections worldwide. Based on the demonstrable impact on child development, there is a global commitment to finance and implement control strategies with a focus on school-based chemotherapy programmes. The major obstacle to the implementation of cost-effective control is the lack of accurate descriptions of the geographical distribution of infection. In recent years, considerable progress has been made in the use of geographical information systems (GIS) and remote sensing (RS) to better understand helminth ecology and epidemiology, and to develop low-cost ways to identify target populations for treatment. This review explores how this information has been used practically to guide large-scale control programmes. The use of satellite-derived environmental data has yielded new insights into the ecology of infection at a geographical scale that has proven impossible to address using more traditional approaches, and has in turn allowed spatial distributions of infection prevalence to be predicted robustly by statistical approaches. GIS/RS have increasingly been used in the context of large-scale helminth control programmes, including not only STH infections but also those focusing on schistosomiasis, filariasis and onchocerciasis. The experience indicates that GIS/RS provides a cost-effective approach to designing and monitoring programmes at realistic scales. Importantly, the use of this approach has begun to transition from being a specialist approach of international vertical programmes to becoming a routine tool in developing public sector control programmes. GIS/RS is used here to describe the global distribution of STH infections and to estimate the number of infections in school-age children in sub-Saharan Africa (89.9 million) and the annual cost of providing a single anthelmintic treatment using a school-based approach (US$5.0-7.6 million). These are the first estimates at a continental scale to explicitly include the fine spatial distribution of infection prevalence and population, and suggest that traditional methods have overestimated the situation. The results suggest that continent-wide control of parasites is, from a financial perspective, an attainable goal.

Filaria control and elimination: diagnostic, monitoring and surveillance needs

Gold standard diagnosis using blood films or skin snips has dimished relevance as mass drug distribution programmes for control of filaria infections expand. The view of 'diagnosis' and its relevance at the individual level has changed, as it has been recognised that the spectrum of programmatic processes (mapping, mass drug interventions, monitoring and evaluation, and surveillance) require different approaches as different questions are asked at each stage. The feasibility and relevance of skin biopsy or blood film examination is challenged when mass drug distribution seeks to treat all eligibles in communities. The need to expand programmes rapidly by identifying the highest risk communities has seen the development of rapid assessment methods, such as rapid epidemiological mapping of onchocerciasis (REMO) and rapid epidemiological assessment (REA) for onchocerciasis, immunochromatographic test (ICT)-based mapping for lymphatic filariasis (LF), and Rapid Assessment Procedure for Loiasis (RAPLOA) for Loa, to reduce the risk of serious adverse events and to guide projects in high-risk communities. As programmes reduce the prevalence through mass drug distribution, more sensitive techniques are required to define endpoints, for LF in particular where the programmatic goal is elimination; for onchocerciasis, sensitive surveillance tools are required particularly in those areas where such risks of recrudescence are high. Whilst much progress has been made in the development and deployment of rapid methods, there are still specific needs for antigen detection in onchocerciasis, whilst standardisation of a panel of tools for LF will allow the definition of endpoint parameters so that countries can decide when mass drug administration (MDA) can be stopped and have a sensitive post-MDA surveillance system.

Surveillance of arthropod vector-borne infectious diseases using remote sensing techniques: a review

Epidemiologists are adopting new remote sensing techniques to study a variety of vector-borne diseases. Associations between satellite-derived environmental variables such as temperature, humidity, and land cover type and vector density are used to identify and characterize vector habitats. The convergence of factors such as the availability of multi-temporal satellite data and georeferenced epidemiological data, collaboration between remote sensing scientists and biologists, and the availability of sophisticated, statistical geographic information system and image processing algorithms in a desktop environment creates a fertile research environment. The use of remote sensing techniques to map vector-borne diseases has evolved significantly over the past 25 years. In this paper, we review the status of remote sensing studies of arthropod vector-borne diseases due to mosquitoes, ticks, blackflies, tsetse flies, and sandflies, which are responsible for the majority of vector-borne diseases in the world. Examples of simple image classification techniques that associate land use and land cover types with vector habitats, as well as complex statistical models that link satellite-derived multi-temporal meteorological observations with vector biology and abundance, are discussed here. Future improvements in remote sensing applications in epidemiology are also discussed.

Diagnostic problems in a patient with amicrofilaremic Loa loa

We report a Japanese patient with loiasis who became infected in Cameroon. Despite the clinical history and laboratory data providing adequate evidence for suspecting loiasis, microfilariae were not detected in the blood. It is important to note that most infected travelers whose home countries are in nonendemic regions are amicrofilaremic.

The Mectizan Donation Program - highlights from 2005

Through the Mectizan^® Donation Program, Merck & Co., Inc. has donated Mectizan (ivermectin, MSD) for the treatment of onchocerciasis worldwide since 1987. Mectizan has also been donated for the elimination of lymphatic filariasis (LF) since 1998 in African countries and in Yemen where onchocerciasis and LF are co-endemic; for LF elimination programs, Mectizan is co-administered with albendazole, which is donated by GlaxoSmithKline. The Mectizan Donation Program works in collaboration with the Mectizan Expert Committee/Albendazole Coordination, its scientific advisory committee. In 2005, a total of 62,201,310 treatments of Mectizan for onchocerciasis were approved for delivery via mass treatment programs in Africa, Latin America, and Yemen. Seventy-seven percent and 20% of these treatments for onchocerciasis were for countries included in the African Programme for Onchocerciasis Control (APOC) and the former-Onchocerciasis Control Programme in West Africa (OCP), respectively. The remaining 3% of treatments approved were for the six onchocerciasis endemic countries in Latin America, where mass treatment is carried out twice-yearly with the goal of completely eliminating morbidity and eventually transmission of infection, and for Yemen. All 33 onchocerciasis endemic countries where mass treatment with Mectizan is indicated have ongoing mass treatment programs. In 2005, 42,052,583 treatments of co-administered albendazole and Mectizan were approved for national Programs to Eliminate LF (PELFs) in Africa and Yemen. There are ongoing PELFs using albendazole and Mectizan in nine African countries and Yemen; these represent 35% of the total number of countries expected to require the co-administration of these two chemotherapeutic agents for LF elimination. In Africa, the expansion of existing PELFs and the initiation of new ones have been hampered by lack of resources, technical difficulties with the mapping of LF endemicity, and the co-endemicity of LF and loiasis. Included in this review are recommendations recently put forward for the co-administration of albendazole and Mectizan in areas endemic for LF, loiasis, and onchocerciasis.

Control of Onchocerciasis

Onchocerciasis is a filarial infection which causes blindness and debilitating skin lesions. The disease occurs in 37 countries, of which 30 are found in Africa (the most affected in terms of the distribution and the severity of the clinical manifestations of the disease), six in the Americas and one in the Arabian Peninsula. The latest WHO Expert Committee on Onchocerciasis estimated that in 1995 around 17.7 million persons were infected, about 270,000 of whom were blind and another 500,000 severely visually impaired. The disease is responsible for 1 million DALYs. Eye disease from onchocerciasis accounts for 40% of DALYs annually although severe skin disease is also recognized as of public health significance. Great progress has been made in the last thirty years in the control of onchocerciasis, both in Africa and the Americas, and this progress has been due largely to international public-private partnerships, sustained funding regional programmes, and new tools and technology. Landmarks in the global control of river blindness include the significant success of the Onchocerciasis Control Programme of West Africa (1975-2002), and the donation of ivermectin (Mectizan) by Merck & Co. Inc., in 1988, a medicine that is distributed to millions free of charge each year. Future major technical challenges of onchocerciasis control include ivermectin mass administration in areas co-endemic for the parasite Loa loa in the light of possible severe adverse reactions, ivermectin treatment in hypoendemic areas hitherto excluded from African control programmes, sustainability of ivermectin distribution, post-control surveillance for recrudescence detection, surveillance for emergence of resistance, and decisions of when to stop mass ivermectin treatments. There is the need to develop the appropriate information systems and diagnostic tools to help in accomplishing many of these tasks. A search for a second-line treatment or as an additional drug to ivermectin as well as a search for a macrofilaricide are issues that need to be addressed in the future.

Public–private partnerships in blindness prevention: reaching beyond the eye

The control of river blindness (onchocerciasis) has been one of the major public health achievements of recent decades. Initially, vector control was used to stop transmission of the parasite Onchocerca volvulus by blackflies (Simulium) but the introduction of ivermectin (Mectizan) as a means of morbidity control enabled new strategies of distribution to be developed based on community directed treatment. The donation of Mectizan by Merck & Co. Inc. for onchocerciasis control in 1987 'as long as needed' was a public health landmark to be followed by a donation from GlaxoSmithKline of albendazole in 1997 for lymphatic filariasis to which Merck also responded by agreeing to extend their donation to include the coadministration of Mectizan and albendazole. Both the drugs, however, have wider impacts than those specific to filarial parasites and are effective against a range of intestinal parasites, whilst ivermectin has an important effect on ectoparasites. The wider benefits of the annual public health intervention-collateral benefits--therefore include deworming, improved nutritional status, increased growth, improved school performance and attendance, and improved haemoglobin status as a result of the impact of albendazole on hookworm, a major cause of anaemia. More recently, studies suggest that worm-free children have a significantly reduced frequency of malaria specific episodes of fever and Ascaris-infected children have a two-fold higher frequency of cerebral or severe malaria than those without Ascaris. These findings suggest that programmes based on annual interventions to control river blindness and lymphatic filariasis can contribute disproportionately more to a range of public health problems than has been hitherto recognized, thereby assisting in attaining the millennium development goal targets.

Structure of the microfilarial reservoir of Loa loa in the human host and its implications for monitoring the progr,ammes of Community-Directed Treatment with Ivermectin carried out in Africa

This paper describes the structure of the microfilarial reservoir of Loa loa in an endemic population of central Cameroon. The possible effects of age and sex on the prevalence and intensity of microfilaraemia have been explored. Logistic analysis showed that the prevalence of microfilaraemia increased significantly with age, reaching 60 % in the oldest males. This result suggests that the figure commonly reported, according to which only one third of the infected individuals were microfilaraemic, should be reconsidered; in addition, as part of surveys of loiasis, crude microfilaraemia prevalence values should be replaced by adjusted ones. The intensity of infection did not show any age-specific change. As a result, even if the oldest members of the male population are clearly the most at risk of developing post-ivermectin serious adverse reactions, especially Loa-encephalopathy, the other members of the population are not risk-free. Therefore, in those areas where the African Programme for Onchocerciasis Control is undertaking regular mass distributions of ivermectin for onchocerciasis control, and where loiasis is co-endemic, no subpopulation should be excluded from surveillance and monitoring during community directed treatments with ivermectin.

Mapping the distribution of Loa loa in Cameroon in support of the African Programme for Onchocerciasis Control

Background

Loa loa has recently emerged as a filarial worm of significant public health importance as a consequence of its impact on the African Programme for Onchocerciasis Control (APOC). Severe, sometimes fatal, encephalopathic reactions to ivermectin (the drug of choice for onchocerciasis control) have occurred in some individuals with high Loa loa microfilarial counts. Since high density of Loa loa microfilariae is known to be associated with high prevalence rates, a distribution map of the latter may determine areas where severe reactions might occur. The aim of the study was to identify variables which were significantly associated with the presence of a Loa microfilaraemia in the subjects examined, and to develop a spatial model predicting the prevalence of the Loa microfilaraemia.

Methods

Epidemiological data were collected from 14,225 individuals living in 94 villages in Cameroon, and analysed in conjunction with environmental data. A series of logistic regression models (multivariate analysis) was developed to describe variation in the prevalence of Loa loa microfilaraemia using individual level co-variates (age, sex, μl of blood taken for examination) and village level environmental co-variates (including altitude and satellite-derived vegetation indices).

Results

A spatial model of Loa loa prevalence was created within a geographical information system. The model was then validated using an independent data set on Loa loa distribution. When considering both data sets as a whole, and a prevalence threshold of 20%, the sensitivity and the specificity of the model were 81.7 and 69.4%, respectively.

Conclusions

The model developed has proven very useful in defining the areas at risk of post-ivermectin Loa-related severe adverse events. It is now routinely used by APOC when projects of community-directed treatment with ivermectin are examined.

Spatial analysis for epidemiology

Remote sensing, geographical information systems (GIS) and spatial analysis provide important tools that are as yet under-exploited in the fight against disease. As the use of such tools becomes more accepted and prevalent in epidemiological studies, so our understanding of the mechanisms of disease systems has the potential to increase. This paper introduces a range of techniques used in remote sensing, GIS and spatial analysis that are relevant to epidemiology. Possible future directions for the application of remote sensing, GIS and spatial analysis are also suggested.

Research for control: the onchocerciasis experience

Onchocerciasis control has been very successful in Africa and research has played a critical role. An overview of the main epidemiological and implementation research activities undertaken over the last 20 years in collaboration with the African onchocerciasis control programmes and of the impact this research had on control is given. The research included the development of epidemiological modelling and its application in programme evaluation and operational planning, research on disease patterns and disease burden in different bioclimatic zones to justify and guide control operations, community trials of ivermectin to determine its safety for large-scale use and its impact on transmission, rapid assessment methods to identify target communities for treatment and community-directed treatment for sustained drug delivery. Lessons learned during this unique collaboration between research and control are discussed.

Impact of ivermectin on illness and disability associated with onchocerciasis

The Onchocerciasis Control Program (OCP), one of the most successful vertical disease control programs in the history of public health, came to an end in 2003 with devolvement of responsibilities for control program activities passed to the countries affected. Fortunately, 15 years ago the Mectizan Distribution Program (MDP) was founded to provide a complementary approach to controlling the disabling consequences of this parasitic infection. With over 250 million doses of ivermectin distributed over the past 15 years, the MDP is well on its way to both solidifying the progress made by the OCP and extending program reach well beyond the boundaries of the OCP. Through the extensive clinical testing protocols implemented in a variety of countries in Aftica, ivermectin has been proven to be a safe and highly effective treatment for onchocerciasis. Regular distribution to populations living in endemic areas has demonstrated significant reductions in blinding ocular complications, transmission, and disability caused by onchocercal skin disease. As yet undocumented, are the likely significant impact regular population dosing with ivermectin has on intestinal helminth infections, lymphatic filariasis, and human scabies infection. While there are significant barriers to continued program success, focussed attention on expanding and improving community-directed ivermectin distribution is likely to lead to further progress against this resilient infection.

Heterogeneity in the prevalence and intensity of loiasis in five contrasting bioecological zones in Cameroon

The prevalence and intensity of loiasis were studied in 4532 individuals selected from 42 villages from 5 contrasting bioecological zones in Cameroon from February to July 2001. The individuals were examined for Loa loa microfilaraemia using the thick blood film method. Loiasis was heterogeneously distributed from one bioecological zone to another. The occurrence of the infection was largely related to environmental factors favouring the breeding of Chrysops vectors. The mean prevalence of infection varied from 0% in the grassland savannah, 6.6% in the deciduous equatorial rainforest, 9.7% in the dense-humid equatorial rainforest, to 33.3% in the forested savannah. Loiasis was totally absent in the grassland savannah. The intensity of loiasis infection (L. loa microfilariae per millilitre [mf/mL] of blood) increased with an increase in prevalence, varying from 0 mf/mL in the grassland savannah, 325 mf/mL in the deciduous equatorial rainforest, 433 mf/mL in the dense-humid equatorial rainforest, to 3125 mf/mL in the forested savannah. The proportion of individuals with high (> 8000 mf/mL) and very high (> 30,000 mf/mL) L. loa microfilaraemia was greater in bioecological zones with a higher prevalence of L. loa. These results will be valuable for the prediction of loiasis endemicity in different ecological zones of Central Africa and for the refinement of the existing geographical model for the mapping of loiasis.

Survenue d’hémorragies rétiniennes lors du traitement de l’onchocercose par l’ivermectine chez une patiente co-infectée par la loase

A case of retinal hemorrhages with special features and degradation of the general condition is reported in a 27-year-old female patient, following the ingestion of ivermectin for the treatment of onchocerciasis. The patient was infested by both Onchocerca volvulus and Loa loa. A bilateral peripheral temporal location of the retinal lesions was observed. The role of L. loa microfilarial load in the occurrence of the retinal lesions as well as the transient character of the lesions are discussed, based on the clinical observation and with reference to the literature. The authors call for setting up a rapid therapeutic system to take care of serious adverse reactions following treatment with ivermectin in areas with a high prevalence of L. loa infestation.

Serious adverse events following treatment with ivermectin for onchocerciasis control: a review of reported cases

This paper presents a summary of reported cases of Serious Adverse Events (SAEs) following treatment with Mectizan(R) (ivermectin, Merck, Sharpe & Dohme) in onchocerciasis mass treatment programs from January 1, 1989 to December 31, 2001 through a passive surveillance system. A total of 207 SAE cases were reported out of approximately 165 million reported treatments delivered during the period under review, giving rise to a cumulative incidence of 1 reported SAE per 800,000 reported treatments. The mean age was 40 years and 70% of the cases were males. The mean time between ivermectin intake and onset of illness was 1 day. For 57% of the cases (n = 118), that was their first exposure to ivermectin. The majority of cases were reported from Cameroon (n = 176; 85%) with peaks in the incidence of SAE reporting in 1989-1991 and 1994-1995 when the program expanded to ivermectin-naïve populations. Fifty-five percent of the cases from Cameroon (i.e. 97 out of 176 cases) were encephalopathic and were reported from the central-southern region of the country; two-thirds of these cases were 'probable' or 'possible' cases of Loa loa encephalopathy temporally related to ivermectin treatment. Reporting bias may explain some but not all of the differences in SAE reporting between the 34 onchocerciasis-endemic countries that have, or have had, mass treatment programs. Further research is needed to understand the apparent clustering of encephalopathy cases in central-southern Cameroon since L. loa infection alone probably does not explain the increased incidence of this type of SAE from this region.

A Framework for Decision-Making for Mass Distribution of Mectizan(R) in Areas Endemic for Loa loa

BACKGROUND: The occurrence of Loa loa encephalopathy following mass treatment of onchocerciasis with Mectizan(R) has adversely affected onchocerciasis control efforts in central Africa. Persons with very high densities of L. loa microfilaremia are at increased risk of encephalopathy, but little is known about the geographic distribution of these persons within central Africa. RAPLOA, a new technique that correlates the proportion of community members reporting a history of eyeworm with the prevalence of high-intensity L. loa microfilaremia in that community, may be useful for rapid assessment of areas at potential risk of treatment-related L. loa encephalopathy. Validation of RAPLOA is ongoing. The operational and risk-reduction advantages of RAPLOA over the current technique of village-by-village rapid epidemiologic assessment for onchocerciasis (REA) are unknown. METHODS: We developed a decision model to compare four strategies for minimizing sequelae of L. loa encephalopathy following mass treatment with Mectizan(R) in areas co-endemic for onchocerciasis and loiasis: REA; RAPLOA with threshold eyeworm prevalences of 40% and 20% (RAPLOA-40 and RAPLOA-20, respectively); and combined REA/RAPLOA-40. RESULTS: In the model, all four strategies significantly reduced risk of death and neurologic complications from L. loa encephalopathy, but RAPLOA-20 and REA resulted in half as many such cases as did RAPLOA-40 or combined REA/RAPLOA-40. CONCLUSION: RAPLOA is likely to be useful programmatically in reducing risk of L. loa encephalopathy following mass treatment with Mectizan(R). It also may be cost-saving. Before full-scale implementation, additional data are needed on geographic clustering of high-density L. loa microfilaremia and on RAPLOA's reliability and cost.

Variation in incidence of serious adverse events after onchocerciasis treatment with ivermectin in areas of Cameroon co-endemic for loiasis

OBJECTIVE

To determine the incidence of serious adverse events (SAEs) after mass treatment with ivermectin in areas co-endemic for loiasis and onchocerciasis, and to identify potential risk factors associated with the development of these SAEs, in particular encephalopathic SAEs.

METHODS

We retrospectively analysed SAEs reported to have occurred between 1 December 1998 and 30 November 1999 in central-southern Cameroon by chart review, interview and examination of a subset of patients.

RESULTS

The overall incidence of SAEs for the three provinces studied was 6 per 100,000. However, for Central Province alone the incidence of SAEs was 2.7 per 10,000 overall, and 1.9 per 10,000 for encephalopathic SAEs associated with Loa loa microfilaremia (PLERM). The corresponding rates for the most severely affected district within Central Province (Okola) were 10.5 per 10,000 and 9.2 per 10,000 respectively. Symptoms began within the first 24-48 h of ivermectin administration but there was a delay of approximately 48-84 h in seeking help after the onset of symptoms. First-time exposure to ivermectin was associated with development of PLERM.

CONCLUSION

In Cameroon, the incidence of SAEs following ivermectin administration in general, and PLERM cases in particular, varies substantially by district within the areas co-endemic for loiasis and onchocerciasis. More intense surveillance and monitoring in the first 2 days after mass distribution in ivermectin-naïve populations would assist in early recognition, referral and management of these cases. The increased reporting of SAEs from Okola is unexpected and warrants further investigation. Research is urgently needed to find a reliable screening tool to exclude individuals (rather than communities) at risk of PLERM from the mass treatment program.

Potential vectors of loiasis and other tabanids on the island of Bioko, Equatorial Guinea

The biting flies Chrysops dimidiatus Wulp and C.silaceus Austen (Diptera: Tabanidae), vectors of Loa loa (Cobbold) (Nematoda: Onchocercidae) on the African mainland, were found to be widespread on the island of Bioko (Equatorial Guinea) during 1996-2001. These tabanids were particularly prevalent in the southern part of Bioko, indicating potential transmission of loiasis on the island. The only other tabanids previously recorded on Bioko, Tabanus argenteus Surcouf (from 1915) and Haematopota near heptagramma Speiser (from 1933), were also collected. The possibility of loiasis being endemic on Bioko contra-indicates ivermectin treatment of onchocerciasis cases, due to risks of adverse side-effects.

Deforestation and the spatio-temporal distribution of savannah and forest members of the Simulium damnosum complex in southern Ghana and south-western Togo

Spatio-temporal data on cytotaxonomic identifications of larvae of different members of the Simulium damnosum complex collected from rivers in southern Ghana and south-western Togo from 1975 until 1997 were analysed. When the data were combined, the percentages of savannah blackflies (S. damnosum sensu stricto and S. sirbanum) in the samples were shown to have been progressively increasing since 1975. The increases were statistically significant (P < 0.001), but the rates of increase were not linear. Further analyses were conducted according to the collection seasons and locations of the samples, to account for possible biases such as savannah flies occurring further south in the dry season or a preponderance of later samples from northern rivers having more savannah flies. These analyses showed that the increasing trend was statistically significant (P < 0.0001) only during the periods April to June and October to December. The presence of adult savannah flies carrying infective larvae (L3) indistinguishable from those of Onchocerca volvulus in the study zone was confirmed by examinations of captured flies. The percentages of savannah flies amongst the human-biting populations and the percentages with L3s in the head were higher during dry seasons than wet seasons and the savannah species were found furthest south (5 degrees 25'N) in the dry season. Comparisons of satellite images taken in 1973 and 1990 over a study area in south-western Ghana encompassing stretches of the Tano and Bia rivers demonstrated that there have been substantial increases in urban and savannah areas, at the expense of forest. This was so not only for the whole images but also for subsamples of the images taken at 1, 2, 4, 8 and 16 km distant from sites alongside the River Tano. At every distance from the river, the percentages of pixels classified as urban or savannah have increased in 1990 compared with 1973, while those classified as degraded or dense forest have decreased. The possibility that the proportionate increases in savannah forms of the vectors of onchocerciasis, and hence in the likelihood of the transmission of savannah strains of the disease in formerly forested areas, were related to the decreases in forest cover is discussed.

A case of loiasis in Rome

BACKGROUND

Owing to the increase of an immigrant population and of Italian citizens travelling for tourism or on business, it is nowadays possible to observe clinical pictures characteristic of tropical regions, often with indistinct symptoms. One of these is Loa loa infestation, or loiasis, a form of filariasis caused by Loa loa and transmitted by the Chrysops fly. We present the case of a male immigrant from Cameroon. Characteristic symptoms were intense xerosis, mostly of the third inferior part of the legs, intensely pruritic, with numerous lesions from scratching. No benefit was obtained by emollient topics, anti-acarus and systemic antihistamines.

METHOD

Serum samples and Giemsa, haematoxylin, haematoxylin + Giemsa concentration-on-membrane stains, have evidenced the presence of Loa loa microfilariae.

RESULTS

A diagnosis for L. loa (loiasis) infestation was made.

CONCLUSIONS

At the beginning of the migration phenomenon, particularly from Africa, Italian physicians, especially dermatologists, were eagerly looking for 'tropical' diseases; this approach can be defined as 'Salgari's syndrome' from the name of the Italian novelist who, though never travelling out of Italy, had perfectly described environments and habits typical of far away countries. Now, conversely, we have to avoid the opposite approach of considering real tropical diseases as related to social or psychological difficult conditions.

Current status and future prospects of the Global Lymphatic Filariasis Programme

Lymphatic filariasis is recognized as one of the world's most disabling diseases. Adult lymphatic filarial nematodes live for several years; they infest the lymphatic and blood systems, and are transmitted via mosquito vectors. Acute and chronic disease can develop, manifesting as acute inflammation, hydrocoele, lymphoedema and elephantiasis. The development of a global programme for the elimination of lymphatic filariasis (focusing on disease caused by Wuchereria bancrofti) followed a resolution by the World Health Assembly in 1997 that endemic countries should develop programmes to eliminate lymphatic filariasis as a public health problem. This developed from an earlier recommendation by the International Task Force for Disease Eradication in 1993 that lymphatic filariasis was one of six diseases that could, in theory, be eradicated. Herein we review the current status and future prospects of the Global Lymphatic Filariasis Programme, which was launched in 2000.