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SELECTED SUCCESSES IN THE CONTROL OF NEGLECTED TROPICAL DISEASES

Thursday, 24th of May 2012

 

 

• SELECTED SUCCESSES IN THE CONTROL OF NEGLECTED TROPICAL DISEASES

Extract from a longer paper, with full text at http://www.parasitesandvectors.com/content/4/1/234

The Allen and Parker paper [10] on page 94 asks two questions; "Can they [NTDs] be so readily controlled and what has been achieved so far? Our answer to the latter two questions is that, perhaps not surprisingly, things are very much more complicated than is claimed". Below are documented accounts of the successes of NTD programmes, which refute the suggestion that NTDs cannot be readily controlled.

Lymphatic Filariasis has been successfully controlled in China in a population of 350 million people and in the Republic of Korea (South Korea); transmission has also been arrested in several countries where it is no longer a public health problem [54]. WHO [31] has reviewed the status of 9 countries originally classified as endemic but found not to require MDA (Burundi, Cape Verde, Costa Rica, Mauritius, Rwanda, Seychelles, Solomon Islands, Suriname, and Trinidad and Tobago) as there was no evidence of transmission [31]. However, Egypt [70], Togo, Yemen, Cambodia, Vietnam, Maldives, Sri Lanka and 7 Pacific Island nations who implemented MDA early in the programme have reduced transmission and met the criteria of stopping MDA. These countries require transmission assessment surveys as recommended by WHO. WHO has reported that around 500 million treatments are being distributed each year [26] with savings of US$ 24 billion between 2000-2008 [71]. Annual treatments of ivermectin and albendazole are given in Africa where onchocerciasis is co-endemic. In the rest of the world the drugs used are diethylcarbamazine (DEC) and albendazole. Ivermectin and albendazole also have a significant impact against intestinal worms. As a result of the programme up to 2008, 66 million newborns have been prevented from becoming infected, 2.2 million protected from developing clinical disease and 28.7 million who have problems of existing infection have seen their clinical symptoms diminish and not progress to further disability. The most recent data from WHO [31] reported that by the end of 2010, 53 countries had implemented drug distribution programmes of the 72 now recognised endemic countries. Country data reported to WHO for 2010 showed that 622 million people had been targeted for MDA and 466 million had been treated giving a reported coverage of 75%. However, several countries are yet to initiate MDA in Africa.

River Blindness (onchocerciasis) has been eliminated as a public health problem and as a disease of socio-economic importance in 10 West Africa countries, the original area of the Onchocerciasis Control Programme (OCP) protecting a population of some 50 million people; the benefits of the OCP have been quantified as 600,000 cases of blindness prevented, 18 million born free of the risk of blindness, 25 million hectares of arable land reclaimed for settlement and agricultural production. This programme which started in 1974 and continued with uninterrupted donor support until 2002 has been widely recognised as one of the most successful health and development programmes ever executed both in terms of health and development gains but in terms of World Bank investment [72]. Control of blindness and skin disease via the donated drug ivermectin (Mectizan; donated by Merck & Co. Inc) is now reaching over 68 million people each year in 17 countries by the APOC supported by national governments and Non Governmental Development Organisations through over 748,000 community workers trained in 120,000 communities since 1995. In Africa there is evidence that 15-17 years annual distribution of ivermectin has eliminated transmission in Mali and Senegal [73] providing strong evidence that elimination is possible with ivermectin alone. Onchocerciasis is also endemic in 6 countries in Latin America where twice yearly distribution of ivermectin has arrested transmission in 4 foci. in Colombia, Guatemala and Mexico and interrupted transmission in a further 6 other foci [74].

Domestic transmission of Chagas disease due to Trypanosoma cruzi has been controlled in five South American countries by domestic spraying of insecticide against the vector Triatoma infestans, providing economic rates of return of around 30% on the investment in vector control. In Central America, progress has been reported through control of Rhodnius prolixus. Transmission by blood transfusion has been substantially reduced throughout Latin America. Sustaining the advances made and maintaining an effective surveillance system are necessary whilst research for new and effective drugs continues to be a high priority to treat those infected.

Leprosy has been reduced as a public health problem as a result of the use of multidrug therapy of three donated drugs- rifampicin, dapsone and clofazimine. Of the 122 countries considered endemic for leprosy, WHO states that 119 have eliminated the disease as a public health problem (defined as 1 case per/10,000). The 213,000 cases reported are confined to 17 countries reporting more than a 1000 cases/year. The figures suggest a reduction of 90% in endemic countries through case finding and multidrug therapy, which have prevented disabilities in between 1 and 2 million people. Since 1985 some 14.5 million people have been cured through multidrug therapy. The numbers of new cases per year have fallen dramatically [8,41].

Guinea Worm is moving towards eradication. The numbers of cases have been dramatically reduced from over 1 million in 1988 to 1797 in 2010 [42]; countries with ongoing indigenous transmission are Chad, Ethiopia, Mali and Sudan. There are several countries, which have not reported cases during the previous year (Burkina Faso, Cote d'Ivoire, Ghana, Kenya, Niger, Nigeria, Togo) and are considered to be in the pre-certification phase awaiting formal certification as being free of transmission. Post-certification, there is a continued need for surveillance until global eradication is declared. The Weekly Epidemiological Record (WER) of WHO provides monthly reports on data from the remaining endemic countries and those yet to be certified as free of transmission - the pre-certification countries. The latest WER reporting all the country data reported to WHO from 2010 can be found in [42].

Schistosomiasis affects some 200 million people. Intensive control in Egypt has reduced prevalence from around 20% to less than 1-2% using the drug praziquantel (now 0.32 US$/treatment) over the last two decades of both S. mansoni and S. haematobium [59]. Schistosomiasis transmission in Egypt has been largely eliminated over the last five years and control focuses on hotspots of transmission and the result has been a massive reduction in incidence of bladder cancer. China has also made considerable progress and now there are less than 1 million people reported to be infected [75]. Programmes in Africa are now reaching school age children in 17 countries in Africa and initial results show that dramatic reduction in prevalence over a period of 4 years of annual treatment.

A Trachoma programme has been established to eliminate blinding trachoma by 2020 through the SAFE strategy (S = surgery; A = antibiotics; F = facial cleanliness through washing; E = environmental control). Trachoma is endemic in 57 countries and the cost of the disease in terms of lost productivity is estimated at US$ 2.9-5.3 billion/annum. The antibiotic azithromycin (Zithromax) is donated. Three countries have reported reaching their ultimate intervention goal targets (Iran, Morocco and Oman). There is a need for further upscaling in the highest burden countries such as Ethiopia, Nigeria and Sudan. There were 37 million treatments of donated zithromax in 19 countries in 2010 [62].

Human African Sleeping Sickness. Over the period 1999-2009 the numbers of reported new cases of both Trypanosoma brucei rhodesiense and T. b. gambiense sleeping sickness has declined by 65%, the numbers of new cases reported falling from over 28,481 to 9,878. However, these figures are likely to be underestimates because of the remoteness of many endemic areas that may not be covered by regular surveillance. There is evidence that the disease is no longer present in many West African countries probably due to climate change and population pressure on habitat of the tsetse fly vector, Glossina. The problem remains focussed in Central Africa. In 2009 only 2 countries reported over 1,000 cases - DRC and Central African Republic followed by Chad (510 cases), Sudan (376) and Angola (247) - of T. b. gambiense; more extensive surveillance and the availability of treatment provided through WHO of donated drugs is the likely cause of the reduced incidence reported. There remains a need to maintain effective surveillance in historic foci and provide diagnostic tests. There has also been a reported decline in cases of acute T. rhodesiense of 58% in East and Southern Africa 1999-2009, from 619 to 190, a 70% decrease http:/ / www.who.int/ gho/ neglected_diseases/ human_african_trypanosomiasis/ en/ index.html website. The adoption of a cattle treatment and insecticide spraying of cattle as a strategy to reduce the reservoir of human infective parasites in Uganda has had a major impact on transmission of T. rhodesiense to humans [76].

Soil transmitted helminth control targets three nematode worms, which inhabit the gut; hookworm (Necator and Ancylostoma), whipworm (Trichuris) and roundworm (Ascaris) and whose global prevalence is probably greater than all the other NTDs combined. Some 882 million children are estimated by WHO [77] to need preventive chemotherapy (273 million pre school age and 609 million school age). WHO reported that 109.7 million pre-school children (proportion of total 33.7%) and 204 million school age (proportion 29.9%) were treated. The overall coverage around 30% is below the global target number treated, which was 313.7 million in 2009, an increase of over 100 million since 2008. Annual mass drug distribution of the drugs mebendazole or albendazole through deworming programmes usually by school-based delivery have a significant impact on educational achievement, increased growth and weight gain, cognitive and physical performance [32,36,37]. Deworming of pregnant women in the second and third trimester of pregnancy increased child survival at the age of 6 months by over 40% in areas of hookworm endemicity. The costs of these deworming programmes in South East Asia are of the order of 2 US cents/year [63]. The onchocerciasis and lymphatic filariasis programmes also act as deworming programmes as the drugs used have powerful effects on the worms of the gut.