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This Week in The Lancet

  • Volume 377 1719 (2011)
  • May 21, 2011


Emerging Threats To Controlling Neglected Tropical Diseases

Friday, January 21st, 2011

Neglected tropical diseases blight the lives of billions of people and threaten the health of millions more. For years these have evolved hand-in-hand with poverty and cripple impoverished populations, greatly impeding global development outcomes. Lisa McClenaghan has written a riveting article on the subject!

Panel 1: Neglected Tropical Diseases

Buruli ulcer
Chagas disease
Human African trypanosomiasis
Lymphatic filariasis

Introduction The Neglected Tropical Diseases (NTDs) are an ill-defined group of infections which constitute the most common group of diseases afflicting the 2.7 billion people living on less than $2 per day [1]. Not only do they cause significant morbidity, but the socioeconomic burden of these conditions is high [2]. Yet, because the majority of sufferers are poor, voiceless and represent an insignificant market share, these diseases have received little attention until recently, and existing control efforts are inefficient and inadequate [1,3]. In addition, a number of factors such as climate change, ecological change, population growth and drug resistance threaten control efforts, and are expected to increase the prevalence, and distribution, of NTDs unless strategies can be modified to cope with an increasing burden.

Climate change Over the past 100 years, the earth’s average surface temperature has increased by 0.6°C [4], while experts predict that average temperature could further increase by 2100 by between 1.4 and 5.8°C [4]. In the context of NTDs, this is significant because the physiological activity of both vector and parasite are sensitive to climatic changes [5, 6]. For example, dengue and filariasis are transmitted by mosquitoes, which require standing water and a warm ambient temperature to breed, mature and enable virus replication [7]. Global warming will be accompanied by alterations in the hydrologic cycle [6, 8], which will impact upon rainfall and water availability. This will affect the distribution and prevalence of parasites which are transmitted by water-borne vectors, such as schistosomiasis [6]. Similarly, Onchocerca volvulus is transmitted by the black fly, which breeds near bodies of water. Peak biting density is observed during the wet season [6], indicating that we should expect to see an increase in the density of transmission of certain NTDs during extreme rainfall.


Avoidable blindness in Sub-Saharan Africa

Wednesday, March 12th, 2008

Three quarters of blindness in sub-Saharan Africa is due to five treatable or preventable conditions as Justin Sherwin explains

There is a disproportionate amount of blindness in Africa, which is home to 19.8% of the world’s blind but only 11.5% of the population. (1) In 2001, it was estimated that approximately 1% of the continent was blind, defined as bilateral visual acuity <3/60 in the better eye. (2) Precise estimates of the prevalence of blindness are difficult to generate, because such research requires large sample sizes, in order to achieve sufficient statistical power, and are expensive. A novel method, the rapid assessment of avoidable blindness (RAAB), is simple to administer, cost-effective, and has been successfully used in Kenya. (3)

There are many reasons for the importance in treating avoidable blindness. Firstly, the ability to see is a human right, and no one deserves to be needlessly blind. Most of Sub-Saharan Africa is afflicted with poverty, which is an independent risk factor for blindness and is also associated with reduced access to treatment. (4) In the absence of treatment, the cycle of poverty is perpetuated, and acts as a further barrier to socio-economic development. The World Health Organization (WHO) considers the alleviation of avoidable blindness as one of the most cost-effective health interventions. Globally, it is estimated that the VISION 2020 strategy can ultimately save more than $200 US billion.(5)

Through the collaboration of the WHO and the International Association for the Prevention of Blindness (IAPB), the VISION 2020: The Right to Sight Initiative recognised that more than 75% of the blindness in Africa is due to one of 5 treatable and/or preventable conditions. (5) These five conditions comprised cataract, glaucoma, trachoma, onchocerciasis and childhood blindness. Ocular leprosy no longer constitutes a major problem in Africa, but the HIV infection has changed the ophthalmic landscape in some endemic areas, with the emergence of ocular associated manifestations of HIV/AIDS. Other target disease areas for VISION 2020 are low vision, diabetic retinopathy, refractive error and age-related macular degeneration, but a discussion on these is beyond the scope of the article. VISION 2020 is the global initiative for the elimination of avoidable blindness by the year 2020, and has an international membership of non-government organizations (NGO’s), professional organizations, eye care institutions and corporations. The overall objectives of VISION 2020 are to identify and educate individuals and organizations about the causes of preventable blindness within a particular country and to provide sufficient resources to prevention, treat and provide rehabilition to those in need. (5)

Cataract is any opacity of the lens in the eye, and is the leading cause of blindness in the developing and developed world. (1) In Sub-Saharan Africa, the prevalence of bilateral blinding cataract is estimated at 0.5%. (2) Unfortunately, the incidence of cataract in the developing world far outweighs the numbers who are being treated surgically. (6) In Sub-Saharan Africa, the cataract surgical coverage (CSC), a measure of the distribution of cataract surgery to those awaiting surgery in a given time period, is poor. (7) In order to monitor the surgical output in a given community each year, the cataract surgical rate (CSR) is calculated. This is usually quoted in the number of operations performed per year, per million persons. In 1999, it was estimated that Africa had the lowest CSR in the world at 300 operations/ million/ year, with the highest CSR’s estimated to be in developed regions. (7)

At present, nearly all surgery performed uses the insertion of an artificial plastic lens following the lens removal, using either an intracapsular or extracapsular approach. Surgery using phaecoemulsion technology is now the gold standard for most cases of cataract surgery in the developed world, however, is rarely seen in Africa due to high cost and complexity required to use it. Access to the low-cost plastic intraocular lens device has improved dramatically due to the installation of lens factories in developing settings, including India and Eritrea. Treatment of cataract blindness is a priority of many eye care NGO’s because it is cheap, quick, effective and relatively simple. Before the widespread implementation of the intraocular lens, cataract surgery consisted of removing the cataract lens and wearing thick, plus powered glasses in order to deal with the resultant high hypermetropia (long-sightedness). Uncorrected or undercorrected aphakia (state when no lens is present within eye) continues to be a problem in some communities. ‘Couching,’ the unorthodox process of manually pushing the cataract lens into the posterior chamber of the eye, is common in some African communities, and can often result in serious ocular complications.

Barriers to ensuring that persons with vision-impairing cataract receive surgical care, include economic reasons, access to healthcare services, lack of knowledge about the surgery and psychological issues. Further efforts at reducing the surgical backlog should focus on training suitable personnel, improving existing healthcare services and creating new healthcare services, and increasing the availability of surgical equipment to areas in need.

Childhood blindness
The most common aetiology avoidable childhood blindness in Malawi has been shown to be corneal pathology due to Measles/ Vitamin A deficiency. (8) Some countries in Sub-Saharan Africa do not have such a problem with Vitamin A deficiency because of diets high in Vitamin A foodstuffs such as red bean oil. Other common causes of childhood blindness in Sub-Saharan Africa include ophthalmia neonatorum (due to chlyamydia or gonorrhoea infection), trauma, uncorrected refractive error, (congential or juvenile) glaucoma, trachoma, corneal scarring, cataract, trauma and genetic eye diseases. (7)

There are several mechanisms by which the burden of childhood blindness in Africa can be reduced. These include distribution of Vitamin A capsules at health clinics, measles vaccination, avoidance of harmful traditional medicine practices to prevent corneal disease, ocular prophylaxis to prevent neonatal conjunctivitis and the ‘SAFE’ strategy for trachoma eradication (see below), in addition to providing health education to parents.

Glaucoma is a heterogeneous group of conditions characterised by a ‘cupped’ appearance of the optic nerve and a corresponding visual field deficit that is typically, but not always, associated with elevated intra-ocular pressure. It is the second most common cause of bilateral blindness worldwide of whom more than 10% of which are considered to be blind.(1) Genetic factors play an important role in the aetiology of the disease, and the prevalence of glaucoma worldwide is highest in those of African descent. (9)

Detection of disease is hampered by lack of sensitive visual field machines in poor and rural settings, and other necessary diagnostic equipment such as slit lamp biomicroscopes with tonometers to measure the intraocular prssure. Patients are often asymptomatic before significant visual loss has occurred, which constitutes a considerable problem in resource poor settings. It may be advantageous to provide opportunistic screening for glaucoma, such as during refractive testing or at the time of ocular surgery for cataract. It is preferable to diagnose glaucoma as early as possible, because early diagnosis is associated with better visual outcomes. Even so, not all persons respond to treatment. Treatment for glaucoma includes medical treatment with ocular hypotensive therapy, surgical treatment that is typically a drainage operation (trabeculectomy) or laser therapy. In Sub-Saharan Africa, the use of ocular hypotensive therapy is restricted due to economic reasons and difficulties with compliance. Surgery is restricted due to cost and lack of trained staff, and laser therapy is restricted due to lack of available facilities.

Trachoma is the world’s leading cause of infectious blindness and is caused by repeated conjunctival infection with Chlamydia trachomatis, and is still prevalent in many countries in Sub-Saharan Africa. Trachoma affects about 84 million people worldwide of whom about 8 million are visually impaired. (10) It is more common in women and children, and typically associated with poor sanitation and hygiene. The present classification of trachoma outlined by the WHO comprises five categories. These are Follicular Trachoma (TF), Intense inflammatory trachoma (TI), Trachomatous scarring (TS), Trachomatous Trichiasis (TT) and Corneal Opacity (CO). Active trachoma is defined as either TF and/or TI.

WHO and the IAPB launched the “SAFE” strategy for Trachoma elimination. This strategy involves Surgery for trichiasis (bilamellar tarsal rotation procedure), Antibiotics (single oral dose azithromycin and tetracycline eye ointment), Facial cleanliness and Environmental improvements (increasing availability/quality of water, decreasing overcrowding, reducing density of flies and improving latrine access). Environmental improvements and antibiotic coverage also assist in the reduction of other infectious diseases, such as Guinea worm. In a critical review on SAFE, the highest support for its use was found in the ‘S’ and ‘A’ components. (11)

However, only limited supplies of tetracycline ointment and azithromycin are available for trachoma eradication in some countries in Sub-Saharan Africa, and the backlog of trachoma surgery is high in some areas. Yet, even when mass antibiotic treatment is not available, environmental and sanitary improvements have led to a reduction in trachoma prevalence in Malawi. (12) Surgery for trichiasis is widely performed by auxiliary ophthalmic personnel. The success of the SAFE strategy relies on donations of Zithromax (azithromycin) from Pfizer, as well as support from government and NGO’s.

Onchocerciasis, commonly known as ‘river blindness’ is disease caused by infection with the microfilariae Onchocerca volvulus that is transmitted via the vector Simulium yahense, a black fly. Globally, there are 37 million people affected, with majority in West, Central or East Africa, and approximately 300000 are blind from disease. (13) Apart from ocular pathology, infection with the microfilariae may also cause skin conditions and other systemic illnesses. Successful treatment of onchocerciasis lies with the administration of a once-a-year dose of the drug ivermectin, which is currently being provided at no cost to all those with this infection from Merck. However, there is emerging evidence that there may be some resistance to the side-effects of this potent drug. (14) Thus, the search for a second-line drug should be key to future management strategies. Also, efforts are underway to reduce the number of blackfly breeding sites through the spraying of larvae with chemicals. Unfortunately, a significant barrier to progress in the fight against onchocerciasis in West Africa has been political and civil unrest that has led to delayed access to treatment.

Tackling the problem
Important principles inherent to VISION 2020 include cost-effective disease prevention, management and rehabilitation interventions, infrastructure (human resources, healhcare facilities, technology, equipment) and funding. (5) These principles should be integrated into existing national healthcare systems and sustainable, equitable and of a high standard. World Sight Day, occuring annually on the second Thursday in October, ensures that members of VISION 2020 raise the profile of blindness as an important international public health issue. Expatriat British ophthalmologist Nick Metcalfe, performed an African continental record of 111 cataract surgeries on World Sight Day in 2006. Such feats give a glimmer of hope for the future of blindness eradication in Sub-Saharan Africa.

Sub-Saharan Africa has a decreased ratio of specialist ophthalmic staff compared to other developing settings, and of course, the developed world. (6) Furthermore, ophthalmologists undertake many different roles including program managers, research scientists and teacher. (2) In order to deal with the gross inadequacy of specialist ophthalmologists, auxiliary ophthalmic staff are crucial team members. For example, Kenya has cataract surgeons who are trained primarily in the treatment of cataract, and who do not have formal medical school training. Ophthalmic nurses, most of whom are able to perform surgery for trachoma, are numerous in Ghana and other countries. Furthermore, in Malawi, the presence of ophthalmic medical assistants has reduced the workload of specialist ophthalmologists, by assisting with cataract surgery. Refractionists are trained specifically in reducing the burden of refractive error associated visual impairment, a role that is partly supplied by optometrists in developed settings.

More than 10 years remains before the year 2020. Whilst the framework for successful blindness eradication of avoidable blindness in Sub-Saharan Africa has been paved, the widespread successful implementation of VISION 2020: The Right to Sight is far from complete. Considerable progress needs to be made before we can live in a world in which no one is needlessly blind.

Justin C Sherwin
Faculty of Medicine, Nursing and Health Sciences
Monash University VIC 3800

(1) Resnikoff S, Pascolini D, Etya’ale D, Kocur I, Pararajasegaram R, Pokharel GP, et al. Global data on visual impairment in the year 2002. Bull World Health Organ. 2004 Nov;82(11):844-51.

(2) Lewallen S, Courtright P. Blindness in Africa: present situation and future needs. Br J Ophthalmol. 2001 Aug;85(8):897-903.

(3) Mathenge W, Kuper H, Limburg H, Polack S, Onyango O, Nyaga G, et al. Rapid assessment of avoidable blindness in Nakuru district, Kenya. Ophthalmology. 2007 Mar;114(3):599-605.

(4). Cook NJ, Rogers NK. Blindness and poverty go hand in hand. Acta Ophthalmol Scand. 1996 Apr;74(2):204-6.


(6) Foster A. Who will operate on Africa’s 3 million curably blind people? Lancet. 1991 May 25;337(8752):1267-9.

(7) Gilbert C, Foster A. Childhood blindness in the context of VISION 2020–the right to sight. Bull World Health Organ. 2001;79(3):227-32.

(8) Gilbert CE, Wood M, Waddel K, Foster A. Causes of childhood blindness in east Africa: results in 491 pupils attending 17 schools for the blind in Malawi, Kenya and Uganda. Ophthalmic Epidemiol. 1995 Jun;2(2):77-84.

(9) Wormald RP, Basauri E, Wright LA, Evans JR. The African Caribbean Eye Survey: risk factors for glaucoma in a sample of African Caribbean people living in London. Eye. 1994;8 ( Pt 3):315-20.

(10) WHO. Report of the 2nd Global Scientific Meeting on Trachoma. Geneva: WHO:2003. 2003; 2003.

(11) Ng WT, Versace P. Ocular association of HIV infection in the era of highly active antiretroviral therapy and the global perspective. Clin Experiment Ophthalmol. 2005 Jun;33(3):317-29.

(12) Hoechsmann A, Metcalfe N, Kanjaloti S, Godia H, Mtambo O, Chipeta T, et al. Reduction of trachoma in the absence of antibiotic treatment: evidence from a population-based survey in Malawi. Ophthalmic Epidemiol. 2001 Jul;8(2-3):145-53.

(13) Burnham G. Onchocerciasis. Lancet. 1998 May 2;351(9112):1341-6.

(14) Osei-Atweneboana MY, Eng JK, Boakye DA, Gyapong JO, Prichard RK. Prevalence and intensity of Onchocerca volvulus infection and efficacy of ivermectin in endemic communities in Ghana: a two-phase epidemiological study. Lancet. 2007 Jun 16;369(9578):2021-9.

37 Million and Counting

Friday, October 26th, 2007

old-man-walking-lushototanzania-pic-aimee.jpgAn old man walking in Lushoto, Tanzania

Onchocerca volvulus, the parasite that causes onchocerciasis, currently infects 37 million people worldwide as Aimée Peck explains

This summer I filmed a documentary in Tanzania to help draw attention to the burden of onchocerciasis, a parasitic disease that causes debilitating blindness and dermatitis.  In the aftermath of a highly effective control campaign initiated in the late 1980′s, the overwhelming perception of onchocerciasis today is that it is a disease of the past.  In fact, onchocerciasis continues to be a very real problem in endemic communities, accounting for the annual loss of 1 million disability-adjusted life-years. (1)  It is imperative that control programs continue to receive the support they need in order to protect the nearly 100 million people who remain at risk of infection. (2) What follows is a discussion of our main findings in Tanzania.  In the spirit of this project, I have used quotations taken from our film to introduce the main issues covered.

“You know, onchocerciasis is one of the neglected tropical diseases, and because it is not a well-publicized disease, sometimes people do not find it necessary to do anything ing about it…” 
John Kilimunana, District Onchocerciasis Coordinator, Muheza District

Onchocerciasis is grouped with schistosomiasis, leprosy, filariasis and a number of other diseases as one of the neglected tropical diseases (NTDs). An estimated one billion people, one-sixth of the world’s population, suffer from these diseases which most often strike the poorest and most vulnerable individuals in tropical and sub-tropical areas. 

Onchocerca volvulus, the parasite that causes onchocerciasis, currently infects 37 million people worldwide (3) and is transmitted from person to person via female blackflies of the genus Simulium.  Although onchocerciasis is endemic in parts of Latin America and Yemen, the African continent carries the greatest disease burden by far.  It is estimated that 300,000 people are blind from onchocerciasis, with 40,000 new cases of onchocercal blindness occurring each year. (4) There is an effective medical treatment for onchocerciasis, ivermectin (MectizanTM), which has been available for free since 1987 through the pharmaceutical company Merck & Co., Inc as part of the Mectizan Donation Program. 

“People could not work, could not sleep…they do not sleep during the night, and when they wake up in the morning, they cannot do anything…”
Harrieth Hamis, Field Coordinator for Tanga CDTI Project

Before mass treatment with ivermectin campaigns began in 1987, onchocerciasis was seen as a significant challenge to development in endemic areas areas.  Blindness and skin disease caused depopulation of fertile land near rivers and in the 1970′s onchocerciasis was presumed to be responsible for annual economic losses of US$ 30 million. 

With the commencement of control strategies in onchocerciasis-endemic areas, prevalence of onchocerciasis was drastically reduced. Populations began reclaiming fertile land and productivity increased accordingly.An estimated US$ 3.7 billion in increased labor and agricultural productivity was observed in participating countries, (5) and the decline in onchocerciasis cases was heralded as one of the greatest success stories in modern medicine.

            “…many people are sick, many others are infected, and the burden of the disease, it is big – but I do not know whether many people know this or not…”
Abdul Daffa, District Onchocerciasis Coordinator, Lushoto District

Community-Directed Treatment with Ivermectin (CDTI) is currently regarded as the most effective long-term treatment solution for onchocerciasis.  It is hoped that after 20-25 years of once-yearly treatment, ivermectin, which kills the infective stage of O. volvulus, will interrupt transmission and onchocerciasis will be eliminated – although some experts believe onchocerciasis will never be eliminated with ivermectin alone and call for research into additional pharmaceuticals. (2)

During our time in Tanzania we uncovered several challenges that threaten the sustainability of CDTI programs.  For example, the work of getting ivermectin to people in endemic villages is carried out by a small number of individuals who receive very little compensation for their essential services. At the village level, two Community Drug Distributors (CDDs) from each village travel to a district drug dispensary to pick up their village’s supply of ivermectin, most times on foot.They are then responsible for personally witnessing the ingestion of ivermectin tablets by every eligible member of their village.  In exchange for this work, the CDDs are compensated roughly what it costs to purchase one soda, per day, for seven days. 

 Many times it takes CDDs more than seven days to complete distribution to the entire village. Once their meager food stipend runs out, they either complete their distribution activities going without food all day, or depend on the generosity of people in the village to feed them. Although their services are greatly appreciated by the other members of the village, we heard many CDDs tell us that more often than not, families simply do not have food or other means of compensation to spare for the CDDs. 

Ivermectin distribution is often scheduled during harvest time to avoid the rainy season, and during distribution the CDDs are taken away from their own fields.  Every CDD we spoke to asked that the government furnish some additional support to balance the costs of distributing ivermectin. Lymphatic filariasis, another neglected tropical disease, is endemic in parts of northeastern Tanzania and the pharmaceutical company GlaxoSmithKline currently donates albendazole for its treatment.  Recently albendazole has been added to the CDTI program for distribution with ivermectin.  One CDD mentioned that a pair of rain boots would help him do his job faster because delays in the arrival of ivermectin or albendazole to the district dispensaries have caused him to have to distribute ivermectin during the rainy season. 

At the district level, the problem of inadequate support is also apparent. Essential duties of the District Onchocerciasis Coordinators (DOCs) include educating communities about onchocerciasis and the importance of taking ivermectin, training of CDDs, procurement of ivermectin, and periodical surveying of onchocerciasis disease burden in their district. When asked what would be the one thing he would ask for that would help him do his job better, a DOC in Muheza told us exasperatedly, “four wheel drive!” Currently, DOCs travel on African Programme for Onchocerciasis Control (APOC)-issued motorbikes.  A four-wheel drive vehicle would significantly improve the ability of the DOCs to reach communities and establish a good working relationship, resulting in greater efficiency of the program.

It has been recognized in the context of onchocerciasis control that involving communities in the management of CDTI is critical for establishing and maintaining program sustainability.(1) (6) These communities are highly sensitized and become extremely efficient at distributing ivermectin; they have achieved treatment coverage rates above 85% in even the most remote areas.  However, these positive outcomes come at a significant cost to the people forming the core of the program who find themselves with more responsibilities but less resources with which to carry out those responsibilities.  This problem will only get worse if a decision is made in the future to include other drugs in addition to albendazole for distribution with ivermectin.  Essential individuals at the district and community levels are not receiving the support they need to continue to distribute ivermectin, and this must change if we hope to continue with CDTI until O. volvulus is eliminated.

            “Sometimes we focus on the killing diseases because we see people being killed     instantly or the disease shows us that the people are dying.  But disease like onchocerciasis, they kill people slowly, and it leaves them more prone to malaria,  HIV, and TB…”
Dr. Grace Saguti, Program Manager, National Eye Care and Onchocerciasis Control Program

Neglected tropical diseases like onchocerciasis cannot be ignored.  Not only do they maim, disfigure, and cause significant mortality in their own right, they can also increase the likelihood that a person will succumb to one of the “faster” killers like malaria, tuberculosis, or HIV/AIDS.  By interfering with an individual’s ability to work and generate income, NTDs chip away at the social safety nets that protect community members from other acute, preventable, or treatable illnesses. If due attention is paid to diseases like onchocerciasis that slowly weaken populations, perhaps we might see an associated reduction in morbidity and mortality from the “big killers” as the ability of the population to cope increases.

Onchocerciasis can teach us much about what can happen when a disease comes close to elimination after a reportedly successful and well-publicized control campaign.  It is a common observation among epidemiologists that the last steps towards elimination of a disease that has been drastically reduced from a formerly pervasive level often becomes paradoxically difficult. With today’s burden of O. volvulus infection at 37 million people, the response to the great successes of the Mectizan Donation Program must be met with a movement to increase support for the types of grass roots drug distribution strategies that have proven to be so successful in Tanzania and elsewhere.

Aimée Peck
97 Kellogg Building
Dartmouth Medical School
Hanover, New Hampshire 03766


(1) World Development Report: Investing in Health. 1993 New York, NY: Oxford University Press.  

(2)African Programme for Onchocerciasis Control.  Final communiqué of the 11th session of the Joint Action Forum of APOC, Paris, France, 6-9 December 2005.   

(3)Basanez MG, Pion SDS, Churcher TS, Brietling LP, Little MP, Boussinesq M. River Blindness: A Success Story under Threat? 2006 PLoS Medicine, Vol 3 Issue 9.

(4)Hopkins AD.  Ivermectin and onchocerciasis: is it all solved?  2005 Eye, No 19 p1057-1066.

(5)Richards FO, Boatin B, Sauerbrey M, Seketeli Azodoga. Control of onchocerciasis today: status and challenges.  2001 Trends in Parasitology, Vol 17 No 12.

(6) Thylefors B, Alleman M.  Towards the elimination of onchocerciasis.  2006 Annals of Tropical Medicine and Parasitology, Vol 100 No 8.