Maladies Tropicales Négligées
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Neglected tropical diseases are, in the main, parasitic diseases that thrive in conditions of poverty and low environmental standards. These diseases impose a heavy burden on populations in the WHO African Region, not only because they are neglected, but also due to the high levels of disability and hence lost productivity they represent to already vulnerable communities. In addition, the chronic nature of neglected tropical diseases places a perpetual burden on weak and overstretched health systems.
Neglected tropical diseases account for 25% of all disability-adjusted life years attributable to infectious and parasitic diseases, and for 10% of mortality. While these diseases constitute a significant public health problem in the communities where they are endemic, their restriction to particular geographic areas and/or environmental conditions often prevents them from acquiring priority status at national level.
The most effective treatment for five commonly occurring neglected tropical diseases is mass-administered preventive chemotherapy over a number of years. Although the cost of such treatment is low, it is still beyond the reach of many governments and individuals, and coverage levels remain too low.
In addition to drugs and health education, other containment measures consist of environmental health improvements, particularly in respect of safe water supply and improved sanitation.
The neglected tropical diseases of most concern in African countries – many of which have received attention through World Health Assembly Resolutions – are Buruli ulcer, guinea-worm disease (dracunculiasis), human African trypanosomiasis, leishmaniasis, leprosy, lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminthiasis and trachoma (including blinding trachoma).
The role played by these and other neglected tropical diseases in perpetuating poverty and stigmatization in poor and vulnerable communities should provide strong impetus to WHO's Global Plan to Combat Neglected Tropical Diseases, 2008–2015.
More than 50% of the estimated global burden of Neglected Tropical Diseases (NTDs) occurs in African countries, and approximately 1 billion people suffer from one or more NTDs worldwide. The heavy and disproportionate burden of NTDs in the African Region affects many communities, resulting not only in heavy morbidity but also in high levels of deformity and disability. In addition, the chronic nature of many NTDs perpetuates the cycle of poverty and imposes a heavy burden on already weak and over-stretched health systems.
The major NTDs occurring in the Africa region include Guinea worm disease, leprosy, lymphatic filariasis, loasis, onchocerciasis, human African trypanosomiasis, and schistosomiasis. Others are soil-transmitted helminthiasis (STH), Buruli ulcer, yaws and other endemic treponematoses, leishmaniasis, trachoma, and endemic zoonoses. These diseases are most prevalent among poor and under-served communities, causing approximately 534 000 deaths annually. Although NTDs may be of public health significance in the communities in which they are endemic, they are often not considered priorities and hence are neglected at all levels – community, national and international.
The incapacitation of NTD patients, as well as the impact on agricultural productivity, grossly contributes to poverty over generations. In terms of Disability Adjusted Life Years (DALYs) and deaths, of the 29% of the global burden attributable to infectious and parasitic diseases, NTDs account for 25% of DALYs and 10% of the deaths. Lymphatic filariasis alone was estimated to result in 4.7 million DALYS annually, according to 2001 data. In economic terms, the price of neglect is too high, as NTDs continue to fuel, in part, the current cycle of poverty, ill health and under-development in the African Region.
Neglected tropical diseases are, largely, long-standing infectious diseases that thrive in impoverished settings, especially in the heat and humidity of tropical climates. Most are parasitic diseases, spread by insects ranging from mosquitoes, blackfly, and snails, to sand flies, tsetse flies, the “assassin bug”, and so-called flies of filth. Others are spread by contaminated water and soil infested with the eggs of worms. NTDs almost exclusively affect poor and powerless people living in rural parts of low-income countries, that is to say those with low literacy and little political voice. These diseases therefore contribute to maintaining the cycle of poverty and stigmatization.
In 2006, WHO launched an Integrated Strategy for Preventive Chemotherapy, based on available, safe and effective drugs that can be administered preemptively to all populations at risk. A preventive chemotherapy strategy employs mass drug administration and is already being rolled out using a variety of methods such as school health days, child health days, vaccination campaigns, community directed treatment initiatives, and other proven mass drug administration activities.
The integrated preventive chemotherapy treatment against five major NTDs (onchocerciasis, lymphatic filariasis, schistosomiasis, soil-transmitted helminthiasis, and trachoma) costs less than 1 US dollar per person per year – a cost-effective intervention. However, even this modest cost is beyond the reach of most resource-constrained nations. Success will depend on uninterrupted access to low-cost medicines and rapid national scaling-up to cover populations at risk.
This strategy is being implemented in countries of the African Region. However, national coverage levels are very low. Ten years after the adoption of Resolution WHA50.29 on the elimination of lymphatic filariasis, the Mass Drug Administration (MDA) coverage in the African Region is low, standing at 16%. The minimum recommended coverage is 65%. Similarly, less than 10% of school age children receive antihelminthic (anthelmintic) drugs.
Buruli ulcer (BU), a debilitating disease caused by Mycobacterium ulcerans, is the third most common mycobacterial disease in healthy humans after M. tuberculosisand M. leprosy. Cases have been identified in at least 22 countries of the African Region since the early 1940s.
In January 1998, WHO established a Global Buruli Ulcer Initiative (GBUI), aimed at developing a global strategy to support affected countries throughout the world in controlling the disease. In May 2004, the World Health Assembly adopted Resolution WHA 57.1 on BU control and surveillance.
By the end of 2005, it was clear that BU, with an estimated 43 000 cases, had become a major endemic disease and a public health problem in WHO African Region.
BU control is based on early diagnosis of cases and treatment with the WHO recommended regimen combining rifampicin and streptomycin, administered daily for 4 or 8 weeks. Late diagnosed cases with large ulcers or bone involvement require further case management through surgery and physiotherapy.
In terms of endemicity, 15 countries are confirmed as BU endemic. Cote Ivoire has reported approximately 22,000 cases. Eleven countries are potentially endemic; these neighbour the previous group and possess similar characteristics that favour BU, such as inter-tropical areas, marshy areas, and forest areas near slow-flowing rivers.
Most affected countries are integrating BU control measures with those for tuberculosis and leprosy, using the same laboratory facilities and supervising staff and logistics at intermediate and district level.
Guinea worm disease
Dracunculiasis (Guinea worm disease) eradication is based on measures recommended in Resolutions WHA39.21 and WHA57.9, and the 2004 Geneva Declaration on Dracunculiasis Eradication.
Dracunculiasis is now close to eradication: the disease is now endemic in only three African countries. Significant progress has been made in the African Region toward the eradication of dracunculiasis, a disease caused by worms of the species Dracunculus medinensis, mainly transmitted through the skin as larval forms while bathing in infested waters. The annual incidence of the disease decreased from 11 882 cases in 2003 to 457 cases in 2009, representing a 91.6% reduction. At the end of 2009, 32 countries were certified free of Guinea worm disease, and seven countries are in the pre-certification stage. Ethiopia, Ghana and Mali are currently the only countries still endemic for Guinea worm disease.
Human African trypanosomiasis
Human African Trypanosomiasis (HAT or sleeping sickness) occurs in 36 countries of sub-Saharan Africa, where over 36 million people are at risk of the disease. The annual incidence is estimated at 450 000, but less than 5% of the population at risk is under surveillance. HAT is caused by a flagellate protozoan parasite – Trypanosoma brucei rhodesiense (especially in east Africa) and T. b. gambiense (in west Africa). Uganda is the only country in the African Region where both species exist. The parasite is transmitted by tsetse flies (Glossina species).
HAT constitutes an important public health problem in 10 of the 36 countries concerned . The disease occurs mostly in remote areas, affecting populations with little or no access to health services. Poor surveillance systems exacerbate the problem.
Leishmaniasis affects more than 300 million people worldwide. It is caused by 20 species pathogenic to humans belonging to the genus Leishmania, protozoa transmitted by the bite of a tiny 2–3 millimetre long insect vector, the phlebotomine sand fly. There are two basic clinical presentations: visceral leishmaniasis (VL), also known as kala azar, and cutaneous leishmaniasis (CL). Cutaneous leishmaniasis tends to resolve spontaneously but causes significant social and psychological stigma. VL is characterized by irregular bouts of fever, substantial weight loss, swelling of the spleen and liver, and anaemia – occasionally serious. If left untreated, the fatality rate in developing countries can be as high as 100% within two years. The African Region is the second largest repository of leishmaniasis, accounting for 17% of the global disease burden.
Leprosy, an infectious and disabling disease, is caused by the Mycobacterium leprae. Transmission of M. leprae is aerial, and takes place directly between persons. It is associated with heavy and negative social stigma due to the physical damage that accompanies complications. The isolation and the social rejection of those infected tend to transform it into a disease of poverty. Promiscuity and poor housing hygiene conditions favour the spread of the disease.
Following Resolution WHA44.9, leprosy has been a major issue among health programmes for the last 10 years, with greatly increased political commitment. Most national leprosy elimination programmes have reached their targets, with the result that there has been a significant overall reduction of the number of leprosy cases in the African Region. All 46 countries have achieved the elimination of leprosy at national level. The number of new leprosy cases has decreased from 52 751 in 2000 to 31 097 in 2008, while the prevalence rate at the end of 2008 was 0.43 cases per 10 000 inhabitants. However, the proportion of children and the proportion of leprosy cases with disability degree 2 have remained at approximately 10% for many years. The disability and stigma attached to the disease are factors that aggravate poverty.
To sustain present achievements and strengthen the quality of leprosy services to further reduce the burden of the disease in Member States, the WHO African Region is developing a new strategy to target the elimination of leprosy at health district level.
Lymphatic Filariasis (LF) is caused by several filarial species dwelling within lymphatic vessels. Found in warm, humid, tropical countries, these filarial parasites are transmitted by mosquitoes. In some regions, they share the same vectors as malaria parasites. In Africa, only one species – Wuchereria bancrofti – is responsible for LF. Of the 120 million infected people in 80 countries worldwide, the African Region accounts for about 38%. In African countries, the main chronic manifestations are hydroceles and lymphoedema/elephantiasis. LF is now recognized as the second major cause of permanent and long-term disability (WHO, 1995).
In recognition of the burden and impact of LF, the World Health Assembly resolved in 1997 to eliminate the disease as a global public health problem within a period of 20 years. As a consequence, a Global Programme for Elimination of Lymphatic Filariasis (GPELF) was launched, and each endemic member country was expected to set up a Programme for Elimination of Lymphatic Filariasis (PELF).
Significant progress has been made towards LF elimination. By 2008, the number of people treated through mass drug administration (MDA) for LF elimination had increased from less than 0.5 million in four countries in 2000 to 57.8 million in 17 countries. Approximately 216.4 million cumulative treatments have been given through mass drug administration schemes (MDA) over the same period, covering 50% of targeted endemic countries. These interventions have led to the reduction of microfilaria prevalence to thresholds of interrupting transmission in Zanzibar, Togo, Comoros, and some districts in Ghana, Burkina Faso and Kenya. However, these efforts represent coverage of only 14% of the total population at risk in Africa.
Onchocerciasis, characterized by skin and eye lesions, is a parasitic disease caused by Onchocerca volvulus. It is transmitted by small black flies of the Genus Simulium that breed in rapidly flowing rivers and streams. The adult parasites have a life span of 8–15 years, during which time they release thousands of microfilariae every year. These microfilariae enter the skin and eyes, causing inflammation and disease. WHO estimates that at least 17.7 million people are infected, 500 000 are visually impaired, and 270 000 blinded from onchocerciasis in 37 endemic countries, of which over 95% are found in Africa.
The main strategy used to control onchocerciasis is Community Directed Treatment with Ivermectin (CDTI) in meso-endemic and hyper-endemic communities. The aim of the treatment strategy is to achieve 100% geographic coverage of endemic areas, in which at least 65% is in meso and hyper-endemic areas.
Figure 4: Community-directed tretment with Ivermectin areas in APOC countries
Ivermectin is a microfilaricidal drug, and in the absence of macrofilaricides, it should be administered over a long period (13–20 years) in order to eliminate onchocerciasis as a public health problem. Therefore, long-term compliance with ivermectin treatment by all eligible communities in both meso-endemic and hyper-endemic areas is crucial in achieving sustainable disease control.
Schistosomiasis, a parasitic disease of man and other mammals, is caused by infections with trematodes of genus Schistosoma. There are five schistosome species that infect humans, and three occur either mainly in Africa (S. haematobium and S. mansoni) or are restricted to the continent (S. intercalatum). Sub-Saharan Africa carries 85% of the global burden of about 200 million infected people; at least 160 million people in 43 African countries suffer from schistosomiasis, and the majority of these are children.
The schistosomiasis control strategy comprises morbidity control through annual mass de-worming exercises to reach all persons residing in the endemic areas, using WHO guidelines. Supportive control measures include intensive health education to the affected communities, and provision of sanitary facilities and safe water especially in schools.
WHO has set a target to treat at least 75% of all school-age children at risk of schistosomiasis and soil-transmitted helminthic infections by 2010. By the end of 2009, eight countries had undertaken mass treatment of whole target populations, while 12 more countries have partially covered populations at risk through mass treatment with Praziquantel.
Almost all Member States in the African Region are endemic for soil transmitted Helminthiasis (STH) to varying degrees. Ascaris lumbricoides, hookworms, and Trichuris trichuria are the most common causative agents. The control of STH is also being revived in the light of new data citing the negative impact on child development and school performance. Resolution WHA 54.19, passed in 2001, called for joint implementation of control of schistosomiasis and STH, with a target of reaching 75% morbidity-control coverage of school-age children by 2010.
The adopted strategy comprises periodic administration of anti-helminthic drugs through school-based, health facility-based, and community-based approaches. The drugs of choice are albendazole or mebendazole. Supporting strategies, as for schistosomiasis control, are health education, and improvements in water supply and sanitation.
Trachoma is one of the oldest known infectious diseases of the eye, with references dating back to ancient Egypt. Trachoma continues to plague the developing world, remaining endemic in the poorest regions. WHO has endorsed a strategy based on surgery for those who already have complications (trachoma trichiasis). Antibiotics (Zithromax, given as a community directly observed treatment to endemic communities), and face washing, improved personal hygiene and environment improvements, are among the most important measures necessary to eliminate blinding trachoma.
State of surveillance
The overall goal of the WHO Joint Strategic Plan for Control of NTDs in the African Region (2010–2015), is to establish strong, sustainable, country-owned programmes capable of achieving the regional and national goals agreed for the control, elimination and eradication of targeted NTDs.
In order to achieve this goal, this Strategic Plan defines four Strategic Areas:
- Strategic Area 1: Strengthen Advocacy, Coordination and Partnerships
- Strategic Area 2: Enhance resource mobilization and Planning for Results
- Strategic Area 3: Scale-up access to interventions, treatment and system capacity building
- Strategic Area 4: Enhance monitoring, surveillance and operations research.
Endnotes: sources, methods, abbreviations, etc.
1. Neglected Diseases : A human rights analysis, WHO, TDR/SDR/SEB/ST/07.2 (2007)
2. Hotez PJ, Molyneux DH, Fenwick A, Ottesen E, Ehrlich Sachs S, Sachs JD. Incorporating a rapid-impact package for neglected tropical diseases with programs for HIV/AIDS, tuberculosis, malaria. PLoS Med 2006;3:e102-e102
3. Engels D & Savioli L (2006) Reconsidering the underestimation of burden caused by neglected tropical diseases. TRENDS in Parasitology, Vol. 22, No. 8.
4. Disease Control Priorities Project (DCCP, World Bank, WHO) 2006.
5. Angola, Republic of Congo, Cameroon, Central African Republic, Chad, Democratic Republic of Congo, Equatorial Guinea, Gabon, Republic of Guinea, Ivory Coast 6WHA Resolution 54.19 (2001)
Tables and figures
Figure 1: HAT Case Reports in AFRO Region (WHO, 2008)
Figure 2: Leprosy prevalence rate in AFRO Region in 2008
Figure 3: Mass Drug Administration for LF (2000-2008)
Figure 4: Community-directed tretment with Ivermectin areas in APOC countries
- ↑ Global Plan to Combat Neglected Tropical Diseases (pdf 291.11kb). Geneva, World Health Organization, 2007
- ↑ Neglected Diseases : A human rights analysis, WHO, TDR/SDR/SEB/ST/07.2 (2007)
- ↑ Hotez PJ, Molyneux DH, Fenwick A, Ottesen E, Ehrlich Sachs S, Sachs JD. Incorporating a rapid-impact package for neglected tropical diseases with programs for HIV/AIDS, tuberculosis, malaria. PLoS Med 2006;3:e102-e102
- ↑ Engels D & Savioli L (2006) Reconsidering the underestimation of burden caused by neglected tropical diseases. TRENDS in Parasitology, Vol. 22, No. 8.
- ↑ Disease Control Priorities Project (DCCP, World Bank, WHO) 2006.
- ↑ Angola, Republic of Congo, Cameroon, Central African Republic, Chad, Democratic Republic of Congo, Equatorial Guinea, Gabon, Republic of Guinea, Ivory Coast
- ↑ WHA Resolution 54.19(2001)