Matt Gribble

Anisha Patel


Project: Mapping socio-political data alongside epidemiological data on onchocerciasis.




Effective control of onchocerciasis in Africa requires consideration of locally complicating factors – the co-endemicity of Loa loa or other diseases, the presence of political instability, and the absence of reliable health infrastructure.  Identification of locations with similar socioeconomic, political, and epidemiological hurdles can result in more efficient and effective control strategies.  This project proposes to provide that information in a visually accessible way, by integrating publically available data with existing maps of the disease burden.


Specific Aims

This project aims to create a better understanding of the distribution of the social, political, and epidemiological factors affecting onchocerciasis control strategies’ success. Treatment of onchocerciasis in communities must be handled on a case-by-case basis, sensitive to the epidemiological, political, and logistical conditions of the community being treated.

The World Health Organization’s Special Programme for Research and Training in Tropical Diseases (TDR) recently developed a mapping program called REMO (Rapid Epidemiological Mapping of Onchocerciasis), which is now integrated with GIS (Geographical Information Systems) to map the prevalence of onchocerciasis in Africa and facilitate strategic thinking about onchocerciasis control.

This project aims to incorporate additional layers of knowledge on the political, social, and epidemiological conditions of African communities into the existing maps of the disease burden.  Specifically, this project will improve on the REMO- GIS maps by adding layers highlighting political instability, perceived quality of health infrastructure, and epidemiological burden of closely related diseases. These improved maps will consolidate more of the data useful to the developers of onchocerciasis control strategies into visually informative tools.



Onchocerciasis, also known as river blindness, is caused by the tissue-dwelling nematode Onchocerca volvulus (Markell and Voge). It is transmitted by blackflies of the genus Simulium, which thrive in rapid-moving waters like rivers (Markell and Voge). The blackfly serves as the intermediate host and vector for O. volvulus (Markell and Voge). After being bitten by the blackfly, the deposited larvae penetrate human skin and find refuge in human subcutaneous tissue in groups of two or more (Markell and Voge).  After about a year of infection, these worms become encapsulated in nodules around the body (Markell and Voge).  Female and male worms reside in these nodules, and the microfilariae (eggs) produced by the worms break free from the nodule and migrate throughout the body in the dermis and connective tissue (Markell and Voge). When a blackfly bites the infected human, it ingests these traveling microfilariae, and the life cycle of the parasite continues (Markell and Voge).  These processes are summarized in Figure 1 (Basáñez et al. 2006).


Fig 1.  Life cycle of Onchocerca volvulus, from Basáñez et al. 2006.


In humans, symptoms of onchocerciasis include onchodermatitis, keratitis, and hanging groin (Markell and Voge). Onchodermatitis is characterized by a papular eruption in which the skin swells and darkens, and then goes on to become wrinkled and atrophic (Markell and Voge).  Perhaps the most infamous symptom of this disease, keratitis (see Figure 2), is a result of the eye lesions caused by microfilarial infection (Markell and Voge). Skin lesions from the Onchocerca infection can also cause loss of dermal elasticity and obstructive onchocercal lymphadenitis, leading to “hanging groin”, depicted in Figure 3 (Markell and Voge).  In Africa (specifically Kenya), microfilariasis endemism levels have been positively correlated to the rates of a visible condition known as “Leopard Skin”, allowing for a cheap and rapid index for assessing levels of onchocerciasis endemism (Edungbola et al. 1987). 


Fig 2.  Keratitis.  Photo Courtesy of Commonwealth Scientific and Industrial Research Organization.


Fig. 3.  Hanging groin.  Photo by the Dr. Murdoch, TDR, World Health Organization.  Image ID:  9403366

File written by Adobe Photoshop® 4.0


The damages of onchocerciasis are subtle, but important.  While onchocerciasis does not result in death, it has very high morbidity, presently affecting more than 18 million people (Basáñez et al. 2006), and life impacts, costing more than 1 million disability-adjusted life years (Boatin and Richards 2006).  The decreasing visual acuity associated with the disease has been correlated to mobility-related, occupational, and relationship difficulties, with social and financial consequences for afflicted persons (Evans 1995).   In addition to these personal losses, there are larger economic losses to society from the abandonment of fertile farmlands near Simulium habitat by persons with no desire to go blind (see Lazdins-Helds et al. 2003); where onchocerciasis endemism has been stamped out, reclamation of abandoned farmlands has yeilded significant economic gains (Kim and Benton 1995).


Onchocerciasis is present in the Americas, Yemen, and Africa, but its epidemiology varies between these areas (Eradicability Report).  In the Americas and Yemen, the disease is currently up for elimination, but in Africa there remain a number of obstacles before whole-regional elimination can be pursued, including a wide migration of infectious blackflies (Eradicability Report).  There has, however, been elimination within Africa on smaller scales (see Molyneux et al. 2003).  This project focuses on the disease in Africa, but acknowledges the existence of the disease in other locales.


The primary treatment strategy for onchocerciasis is ivermectin (Markell and Voge).  Ivermectin does not kill adult worms; instead, it targets microfilaria, preventing effective Onchocerca reproduction (Markell and Voge).  This treatment only requires a single dose each time, but must be periodically repeated until no more reproductively competent adults are present in the infected person (Markell and Voge).  Doxycycline is another treatment option, inhibiting embryogenesis in female Onchocerca worms by killing the Wolbachia bacterial endosymbionts required for Onchocerca reproduction (see Hoerauf et al. 2003).


            Onchocerciasis control efforts have been large-scale partnerships between governments, non-governmental organizations (NGOs) such as the Carter Center and the World Health Organization, drug companies (e.g. Merck & Co., Inc., the manufacturer of ivermectin), and local communities, which bear much of the responsibility for implementing onchocerciasis control programs (Straub, Eradicability Report).  The most effective programs are those which have been initiated by the groups seeking treatment (i.e. national governments), rather than programs suggested and undertaken by outside groups (i.e. aid organizations, NGOs) (Straub).  Effective coordination between all these different stakeholders, and development of regionally appropriate control strategies, requires careful planning at many levels.


            The use of geographic data has greatly facilitated onchocerciasis control efforts.   The rapid epidemiological mapping of onchocerciasis (REMO) program, developed by TDR and now managed by the African Programme for Onchocerciasis Control (APOC), uses geographic information, such as the location of river basins, to identify particularly high-risk areas for the disease (TDR Products website; Noma et al. 2002).  This data has been integrated with Geographic Information System (GIS) maps, which are capable of storing other types of information, such as population distributions, to allow for much more accurate estimates for the distribution and prevalence of the disease (TDR Products website).


However, the current maps are incomplete, and could be improved by the inclusion of additional relevant data. 


Integration of spatial data on other diseases with REMO-GIS maps allows for rapid identification of locales where ivermectin is not an appropriate control strategy.  Loa loa co-infection results in severely adverse responses to ivermectin (see Twum-Danso 2003, Boussinesq et al. 1998), necessitating alternative treatment regimes.  Some efforts to incorporate Loa loa data into GIS-REMO maps have already taken place, but at limited spatial scales and not in conjunction with other potentially useful data.  A 2000 paper by Thomson et al. mapped modeled Loa loa prevelance against REMO data (see Figure 4).  A follow-up study by this same group mapped empirical Loa loa data against the predictive model, allowing for instant recognition of what is known and what is predicted about Loa loa/Onchocerca co-endemism.  (Thomson et al. 2004; see Figure 5).  The Thomson et al. maps are an excellent start, but information about other relevant diseases, including T. solium (see Katabarwa et al. 2008) and HIV/AIDS (Alemnji et al. 2004), should be included as well.  Ideally, information like that presented in Figure 2 should be consolidated for the entire African endemic region, not just a six-country subset.


Fig 4. “Model results indicating prevalence of Loa loa in six countries covered by the African Programme for Onchocerciasis Control”, from Thomson et al 2000.  GIS map linking Loa loa endemism (modeled) to REMO data.



 Handmade Software, Inc. Image Alchemy v1.13


Fig. 5.  “Predictive model of Loa loa prevalence for Cameroon overlaid with the observed prevalence data”, from Thomson et al. 2004.  GIS map reflecting actual Loa loa endemism on top of predicted endemism.



Another useful addition to the REMO-GIS map is social science data.  Political instability and health infrastructure quality data have yet to be integrated into REMO-GIS.


            Political instability can undermine onchocerciasis control efforts.  In Guinea Bissau’s Coruba River Basin, civil unrest in 1997 led to a four month interruption of the area’s three-month-treatment programs (Eradicability Report, Borsoom et al. 2003).  This interruption in ivermectin treatment was followed by statistically significant onchocerciasis revival:  there were increases between 1997 and 2001 both in the area’s infective Simulium sirbanum populations, and in the onchocerciasis prevalence in human populations (Borsoom et al. 2003).  Information on political instability could come in many forms, but one possible free source is the World Bank’s Worldwide Governance Indicators dataset (WBI website).


            Poor health infrastructure has also been identified as a challenge for onchocerciasis control efforts in Africa (Eradicability Report).  Over the past few years Afrobarometer, a joint project between Michigan State University, the National Science Foundation, the Swedish International Development Cooperation Agency, and other groups, has collected survey data on a wide range of social topics (Emory library website, Afrobarometer website).  While the primary goal of these surveys was to measure “the social, political, and economic atmosphere” in Africa (Afrobarometer website), the geographically-coded survey results may help to identify places where health infrastructure is lacking.  Questions on the Round 3 survey, for example, inquired whether there were demands for illegal payments at local hospitals or clinics, a lack of medicines or supplies, or absent doctors (Kirwin 2007).  Identification of places where health infrastructure is lacking may foster brainstorming on alternative, more effective ways to deliver treatment in those areas.


Study Design


Existing REMO-GIS maps lack useful information on Loa loa and other disease co-endemism, political instability, and healthcare infrastructure problems.  Most of this information is publically available, but not yet integrated with the REMO-GIS maps.  Our proposal is to collect this absent information from publically available scientific literature, acquire REMO-GIS maps from the African Programme for Onchocerciasis Control, and, using the ArcGIS software which Stanford already has a site licence for (Seiffert), incorporate the data into the existing REMO-GIS files. 


One of the strengths of this proposed project is that it provides substantial benefits at very little cost.  The greatest costs are up-front, relating to the development of a map from scratch (Seiffert).  Since the REMO-GIS maps already exist, this cost has already been paid.  The other large potential expense is access rights to the data sets of interest (Seiffert).  However, since the Afrobarometer, Thomson Loa loa, and many other relevant data sets are publically available, their use incurs no cost.  Furthermore, since this data would be used for a good cause, it is feasible that groups which might ordinarily charge for their might donate this data for free, analogous to how Merck has pledged to provide free ivermectin for treatment of the disease.  Most of these data are already encoded in ArcGIS or a compatible software (i.e. Excel), and so it would be very easy to import these data into existing REMO-GIS maps (Seiffert).  The primary cost of the project would be labor for inputting data; the total budget to gather and incorporate all these data into an existing GIS map might not exceed $5,000 (Seiffert).

Another benefit to this project is that it can easily accommodate additional concerns, simply by adding additional layers to the map.  As future research identifies additional challenges, data on those challenges can be added as another layer of the modified REMO-GIS map (Seiffert).   Similarly, map layers on Loa loa and other disease co-endemicity can be expanded to broader spatial scales than are currently published, as information becomes available.  Thus, this tool can be quickly responsive to changing inputs and information needs.


This project proposal has focused on the relatively small-scale task of updating maps focusing on onchocerciasis and directly related problems using existing data.  However, much attention is currently being given to tackling the neglected tropical diseases in an integrative, holistic manner (Hotez et al. 2007).  Treatment programs for many of these diseases would benefit from an understanding of the location of other co-endemic diseases, as drugs proscribed for one condition may react negatively with another infection (see Katabarwa et al. 2008;  Kamgno et al. 2008, Thomson et al. 2004).  Data on health infrastructure and political stability are also relevant for many other conditions besides onchocerciasis.  Therefore, the map improvements suggested in this proposal could serve as the foundation for a much broader-scope tool that would help with integrated, multiple-disease targeting health initiatives in Africa.


Works Referenced

"Blind Eye." Photograph. 16 May 2006. Commonwealth Scientific and Industrial Research Organization. 23 May 2008. <>.

Afrobarometer Surveys.  Afrobarometer.  Updated January 14, 2008.  Accessed May 22, 2008. <>.


Dr. Murdoch, TDR, World Health Organization.  Hanging groin.  Phototograph.  Image ID:  9403366  Accessed May 23, 2008.  <>.


Alemnji, AG; Toukam, E; Ayong, L; Wembe, E; and T Asonganyi.  2004.  HIV prevelance and humoral immune status of patients co-infected with HIV and onchocerciasis in Cameroon.  Int Conf AIDS.  2004 July 11-16; 15:  abstract no. ThPeA6934.


Basáñez, María-Gloria; Pion, Sébastian D.S.; Churcher, Thomas S.; Breitling, Lutz, P.; Little, Mark P. and Michel Boussinesq.  (2006).  River Blindness:  A Success Story Under Threat?  PLoS Medicine.  3(9):  e371.


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Boatin, Boakye A. and Frank O. Richards, Jr.  (2006).  Control of Onchocerciasis.  Advances in Parasitology 61: 349-394.


Borsoom, Gerard JJM; Boatin, Boakye A; Nagelkerke, Nico JD; Agoua, Hyacinthe; Akpoboua, Komlan LB; Soumbey Alley, William E; Bissan, Yeriba; Renz, Alfons; Yameogo, Laurent; Remme, Jan HF; and J Dik F Hammeba.  (2003).  Impact of ivermectin on onchocerciasis transmission:  assessing the empirical evidence that repeated ivermectin mass treatments may lead to elimination/eradication in West Africa.  Filaria Journal 2:8.


Boussinesq, Michel; Gardon, Jacques; Gardon-Wendel Nathalie; Kamgno, Joseph; Ngoumou, Pierre; and Jean-Philippe Chippaux.  (1998).  Three probable cases of Loa loa encephalopathy following ivermectin treatment for onchocerciasis.  Am. J. Trop. Med. Hyg. 58(4): 461-469.


Dadzie, Y.; Niera, M.; Hopkins, D.  (2002).  Final Report of the Conference on the Eradicability of Onchocerciasis.  The Carter Center, Cecil B, Day Chapel, Atlanta, USA.  January 22-24, 2002.


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Evans TG.  (1995).  Socioeconomic consequences of blinding onchocerciasis in West Africa.  Bull World Health Organ 73(4):495-506. 


Hoerauf, A; Mand S; Volkmann L; Büttner M; Marfo-Debrekeyi Y; Taylor M; Adjei O; and Büttner DM.  (2003).  Doxycycline in the treatment of human onchocerciasis:  Kinetics of Wolbachia endobacteria reduction and inhibition of embryogenesis in female Onchocerca worms. 


Hotez, Peter J.; Molyneux, David H.; Fenwick, Alan; Kumaresan, Jacob; Sachs, Sonia Erlich; Sachs, Jeffrey D., and Lorenzo Savioli.  (2007)  Control of Neglected Tropical Diseases.  New England Journal of Medicine 357 (10): 1018-1027.


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Katabarwa, Moses; Lakwo, Tom; Habumogisha, Peace; Richards, Frank; and Mark Eberhard.  (2008).  Could Neurocysticercosis be the cause of “Onchocerciasis-Associated” Epileptic Seizures?  Am. J. Trop. Med. Hyg. 78(3): 400-401.


Kamgno, Joseph; Boussinesq, Michel; Labrousse, François; Nkegoum, Blaise; Thylefors, Björn I; and Charles D. Mackenzie.  Encephalopathy after Ivermectin Treatment in a Patient Infected with Loa Loa and Plasmodium spp.  (2008).  Am. J. Trop. Med. Hyg. 78(4):  546-551.


Kim, Aehyung and Bruce Benton.  Cost-Benefit Analysis of the Onchocerciasis Control Program – World Bank Technical Paper #282.  The World Bank.  May 1995. 


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Lazdins-Helds, J.K.; Remme, J.H.F.; and B. Boakye.  (2003).  Focus:  Onchocerciasis.  Nature Reviews Microbiology 1.  178-179.


Molyneux, David H; Bradley, Mark; Hoerauf, Achim; Kyelem, Domanique; and Mark J. Taylor.  (2003).  Mass drug treatment for lymphatic filariasis and onchocerciasis.  Trends Parasitol 19:  627-634.


Noma, M.; Nwoke B.E.B.; Nutall I.; Tambala P.A.; Enyong P.; Namsenyo A.; Remme J.; Amazigo U.V.; Kale, O.O.; Sékétéli, A.  (2002).  Rapid epidemiological mapping of onchocerciasis (REMO):  its application by the African Programme for Onchocerciasis Control (APOC).  Annals of Tropical Ecology and Parasitology vol. 96 Supplement 1:  22-29.


Seiffert, Christopher.  Personal Communication – Cost Estimates for producing GIS maps.  May 7, 2008.


Staub, Emily.  Personal Communication – The Carter Center’s Strategies for Controlling Onchocerciasis.  April 17, 2008.


TDR Products and Outcomes:  rapid mapping for onchocerciasis.  World Health Organization.  Modified January 22, 2008.  Accessed May 22, 2008.  <>.


Thomson, MC; Obsomer, V; Dunne, M; Connor, SJ and DH Molyneux.  (2000).  Satellite Mapping of Loa loa prevelance in relation to ivermectin use in west and central Africa.  The Lancet, vo. 356 no. 9235: 1077-1078.


Thomson, Madeline C; Obsomer, Valérie; Kamgno, Joseph; Gardon, Jacques; Wanji, Samuel; Takougang, Innocent; Enyong, Peter; Remme, Jan H; Molyneux, David H; and Michel Boussinesq.  (2004).  Mapping the distribution of Loa loa in Cameroon in Support of the African Programme for Onchocerciasis Control.  Filaria Journal 4:7.


Twum-Danso, Nana AY.    (2003).  Loa loa encephalopathy temporally related to ivermectin administration reported from onchocerciasis mass treatment programs from 1989 to 2001:  implications for the future.  Filaria Journal 2(Suppl1):S7.


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