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Home , Schistosomiasis

Candidate parasitic diseases K. Behbehani'

This paper discusses five parasitic diseases: American trypanosomiasis (), , lymphatic , onchocerciasts and schistosomiasis. The available technology andhealth infrastructures in developing countries permit the eradication of dracunculiasis and the elimination oflymphatic filariasis due to . Blindness due to and transmission of this disease will be prevented in eleven West African countries; transmission of Chagas disease will be interrupted. A well-coordinated international effort is required to ensure that scarce resources are not wasted, efforts are not duplicated, and planned national programmes are well supported.

Introduction tion or interruption of transmission. This rcquires The Division of Control of Tropical Diseases (CTD) that the disease has been adequately researclhed in in WHO has global responsibility for African terms of the causative organism. clinical impact. trypanosomiasis, Chagas disease, dracunculLasLs manaoement, treatment and epidemiology. The (guinea-worm discase), toodborne trematode infec- change is facilitated by a breakthrough m the form of tions. intestinal parasitic . lIishmaniasis, a new stratcgy and/or tool that can effectively and lymphatic filarnasis, . onchocerciasis and rapidly reduce the incidence of and diseasc schistosomiasis. National programmes to combat using the infrastructures in place. these diseases are supported by WHO, in many in- stances in collaboration with other international Public health strategy agencies. development aid agencies, nonigovern- mental organizations. and industry. The mission of Disease elbmination or eradication piogramnmes have CID. working closely with the WHO Regional Of- to fit wIthin the existing public health strategies The fices. is to provide support to country activities. to essential public health functionis in each counti y promote. advocate and coordinate should include major problems as control with the aim of improving the health status of an integral and coherent part of the ""Renewal of individual communities and populations, and to con- Health for All' process led by WHO tributc to social and economic development. This paper discusses five of the diseases listed Determinants of success or failure above: Chagas disease, dracunculiasis, , onchocerciasis and schistosomiasis. Four of The definitions of success and lailure are never verv these have been targeted for global eliminalion by clear and these terms tend to be used to promote the WVorld Health AssembJy, the objectives being the difterent points ot view. Perhaps the criteria lot interruption of transmission of Cbagas disease by the success or failure should be spelled out from the very year 2010; the eradication of dracunculiasis by 2008, beginniing. TIhere are, however. many factors that the elimination ot lymphatic filariasis by 2020: and determine success or failure, and the major issues ai e the elimiation of onchocerciasis as a public health discussed below. problem in 11 West Al rican countries by 2002. * A oood surveillance system and sensitive responise mechanism are essential to inoliiLor progress. detect epidemics and programme deficielncies, and Criteria for establishing elimination take remedial action. * Researclh is needed to provride I1ie scientific basis programmes upon which to make programme adjustments Technical feasibility is the critenon for chanaing operational research lo answer questionis tlat will from control of ntoction to an objective ot eliniiia- improve progiamme implemenLatioii andl imianL- agement, and basic research to evaluate new tools aincd determiniiie the conditions under which tllev will pr-ovide optinliTu results Director, Division of Control of Tropical DCseases, World Health * Both polilical will and cornmitlmlenLt atre absolltelyt Organization, 1211 Geneva 27, Switzerland essential and these should be demonstrated hby

64 Bulletin of the World Health Orgaa.zafrn, 1998, 76 (Supcl 2) 64-67 Candidate parasitic diseases provision of the necessary resources to implement Dracuncuhis which are released into water when an well-planned programmes with clear strategies infected person steps into it to relieve the pain and in-built evaluation procedures. caused by the emerging worm. The emergence of the adult worm through the skin. usually from the legs c Basic training and continuing education at all and feet, approximately one year afLer the individual levels are crucial. and supervision should be seen concerned drank unsafc water, is extremely painful. as a part of the educational process. The rigbt mix causincg , nausea and vomiting. and disabling of highly trained specialists and generalists and the person for months. systems for motivation are important There are 100 million people still at risk of infec- * Community participation and coordinated na- tion In 1997 alone. approximately 70000 cases were tional and international action are required to reported, compared to the estimated 10 million indi- avoid duplication of effort and to maximize viduals infected per annum before the inception of impact. the eradication programme This drastic reduction is the result of the eftorts made jointly by the countries with WVHO, UNICEF. CDC, Global 2000 and a mul- titude of other NGOs and industry. Althouglh there Chagas disease are no specific drugs to treat or prevent infection. the The objective is the interruption of vectorial and recommended strategy aims at case containment of transfusional transmission in the Amcricas. by the infected individuals, community-based surveillance. year 2010. of the blood-borne parasite Trypanosoma and provision of safe drinking-water through the dis- cniZi wvhicl causes Chagas disease. Natural transmis- tribution and use of cloth filters. sion occurs through the bitc of triatomine bugs and iatrogenically through blood transfusion. The strat- egy, therefore, is to elinminate botb vectorial and Lymphatic filariasis transfusional transmission by the housclold ap- plication of insecticides and through blood bank Lymphatic filariasis, often refcrred to as eleplhantia- screening. sis, causes profound lymphoedema. genital and rcnal There are 16-18 million infected persons in involvement, and secondary bacterial infections, and Central and Soutlh Anmcrica and 100 million people can result in disfigunng enlargcment of the limbs, at risk. Currently, human infectLon of young age breasts. and genitalia. It is endemic in 73 countries, groups has been reduced by 68% over the last 6 years where 120 million people are intected. Worldwide it in the Southern Cone countries (Argentina. Brazil. is estimated that there are 25 million cases of genital Bolivia. Chilc, Paraguay and Uruguay) In 1997. disease and 15 million cases of lymphoedema/el- Uruguay had eliminated tllc vector Triaotoira ephantiasis. The disease is caused by a blood-borne infestans, demonstrating that elimination of trans- infection with the parasitic worms Wu'chereria mission is a teasible goal. bancrofti. Brugia nialayi, and B. timorr, which are A similar initiative for the Andean countries transmitted by various mosquito species. Humans are the only definitive host for WV bancrofti, whiich (Colombia, Ecuador, Peru. and Venezuela) was accounts for 90% of infections. For B. nialayi and B. launclhed in February 1997 with preparation of de- titnori. which account for the remaining 10%. a tailed plans of action and budget for 1998 to 2001. It number of other animals may harbour the parasites. is foreseen that interruption of vectorial and However, the epidemiological role of this in relation transfusional transmission will be acbieved in these to transmission is tllouglht to be small. countries by 2005. Similar efforts for the Central Epidemiologically it has been shown that, where American countries were launched in October 1997; hygiene and environmental improvements predomi- it is foreseen that transmission will be interrupted by nate, there can be a reduction in parasite levels to 2010. below those necessary to sustain local transmission. Introduction of simple treatment regimens can greaLly hasten the interruption of transmission. Largely because of newly available and dramatically Dracunculiasis effectli e trcatment and diagnostic tools, the outlook The disease is caused by a parasitic Xwrorm for filariasis controlUelimination is now so positive Dracrsnculus medinenvis (guinea worm). The infec- that it has been identified as a potentially eradicable tion is acquired by humiians through drinkina water disease. WHO has therefoie embarked upon the containing infected cyclops. This minute crustacean global elimination of lvmphatic filariasis as a public becomes intected by ingestion of the larvae of health problem globally by the year 2020. To this

WHO Bullelin OMS. Vol 76, Suppl 2. 1998 65 K. Behbehanl end. SmithKline Beecham in December 1997 agreed miasis is caused by the flatwornms or blood flukes, to donate albendazole and support the programme mansoni, S. japonicum, S. mekongi and until the disease has been eliminated. S. intercalatum, while urinary schistosomiasis is caused by S. haematobium. People are infected by contact with water used in normal daily activities for personal or domestic hygiene and when Onchocerclasis swimnming, or through occupational activities such Onchocerciasis is caused by infection wvith the filarial as fishing. rice cultivation, and irrigation. The worm , which is transmitted by intermediate hosts are different species of blackflies of the genus Simulium, causing itching and which. when infected, release cercariae into the a disfiguring skin disease. serious eye lesions, and water which can penetrate the intact skin. In the blindness among persons in parts of tropical Africa, human, it is not the worm but the eggs which the Arabian peninsula, and Central and South cause damage to the intestine, bladder, and other America. Although the control of onchocerciasts by organs. the Onchocerciasis Control Programme in West The global distnbution of schistosomiasis has Africa has been highly successful, the disease re- changed significantly over the past 50 years, as a mains endemic in 34 countries. affecting over 17 mil- result of successful control in Asia, the Americas. lion people, 99% of whom are in Africa. At least 6.5 North Afria, and . This success has mlllion people suffer severe itching or dermatitis been consistently linked to both political commit- and at least 270000 are blind because of the worm ment and the implementation of a concerted control infection. strategy. However, schistosomiasis remains endemic The strategy that has been shown to be most in 74 developing countries (600 million people at effective is the annual single-dose treatment of af- risk) and infects more that 200 million people (120 fected populations with the drug ivermecLin, and million with symptoms and 20 million suffering the laniciding against the blackfly vector. In 1997, 18 severe consequences of the disease). The greatest million treatments were given, approximating to concern is in sub-Saharan Africa. where over 80% of 25% coverage. It is possible to sustain this pro- the cases occur. gramme due to a drug donation programme by The main intervention strategy is an integrated Merck & Co. approach using chemotherapy, health education, the The policy aims at prevention of blindness and installation of wells and safe water sources and elimination of onchocerciasis as a public health and latrines, and the control of . Today, the global socioeconomic problem throughout Afrnca and the objective remains control, especially in Africa, Americas, and interruption of onchocerciasis trans- where transmission continues to be intense. More- mission in selected foci. In the eleven Onchocerciasis over, recent environmental changes, closely linked Control Programme countries in . elimi- to water resources development in previously low nation is expected by 2002, and the participating or nonendemic areas and increases in population countries are expected to maintain this. In the Afri- densities, have led to the spread oC thLs disease. can Programme for Onchocerciasis Control covering the remaining endemic countries in Africa, the ob- jective is to have established - by 2005 - effective, self-sustaining, communitv-based ivermectin treat- The rationale ment programmes which will lead to the elimination It has long been realized that dracunculiasis can only of this disease from the rest of Africa. In the be contracted by drinking water that contains in- Onchocerciasis Elimination Programme of the fected Cyclops. Thus, the source of drinking-water is Americas. it is expected that - by 2000- morbidity the crucial link in the cycle. Ever since the Umted will have been reduced and blindness and other Nations launched the Intenational Drinking Water sequelae prevented, leading to the elimination of the Supply and Decade (1981-1990), the pathological manifestations of the disease and inter- possibilitv of dracunculiasis eradication became a ruption of transmission in selected foci. realitv n the Southern Cone countries of South America, the vector of Chagas disease is found in- side houses in close proximitv to humans and control Schistosomiasis of transmission has proved to be amenable by use of Schistosomiasis is a parasitic waterborne trematode insecticides, house design, and routine blood screen- infection causing chronic ill health and affecting the ing. In the Andean and Central American countries, urinary or intestinal system. Intestinal schistoso- the habits of the vector species are more ju6 WHO Bulletin OMS Vi 76, Suppl 2, 1998 Candidate parasitic diseases extradomiciliary so that vector control will be more among those diseases listed for elimination in the difficult and progress slower. next two decades. The decision to includc lymphatic filariasis as a disease for global elimination was taken, based on advances during the last decade or two in diagnosis, Conclusions clinical understanding, treatment and control of this disease, as well as the increasing political commit- The available tecbnology and health infrastructures ment by Member States. Today, interruption of in developing countries permit the eradication of transmission can be achieved by treating infected dracunculiasis and the elimination of lymphatic persons and by mass treatment of the population at filariasis due to W. bancrofti, wbich will benefit risk. The mainstay of the elimination strategy is the present and future generations. Progress in control- use of simple, safe, inexpensive and conveniently ling infections due to B. malayi and B. timori WLIIl delivered drugs that kill microfilariae and that have depend upon future studies on the impact of the some effect on the adult worms. epidemiological overlap between the animal and The very successful Onchocerciasis Control human infection Persons now suffering from el- Programme in West Africa was well funded and ephantiasis will require special case management. well managed The advent of the drug ivermectin. Blindness due to onichocerciasis will be prevented the initiation of the Mectizan Donation Programme. and disease transmission will be interrupted in the the participation of the ministries of health. eleven West African countries which were in the nongovernmental organizations, W7HO and other original Onchocerciasis Control Programme. Trans- collaborating agencies in drug distribution pro- mission of Chagas disease will also be interrupted, grammes, and rapid epidemiological assessment leaving a residue of chronic sufferers to be managed techniques and mapping methods have given nse to by the health services. well-founded optimism. Thus, mterruption of trans- The lessons learned from present attempts to mission in selected foci is feasible in these areas in a eradicate/eliminate/interrupt transmission of the relatively short space of time wvith a combination of above-mentioned four diseases and the health drug therapy and vector control. In the remaining service systems that are strengthened in the process countries ot Africa and in the Americas, the pro- should contribute to the elimination/eradication of grammes are at the early stage of development and other tropical diseases in the not too distant future. implementation. The efficiency and effectLveness ofprogrammes must Schistosomiasis remains difficult to control be strengthened so that the gains achieved can be because environmental changes which are taking sustained in the long tcrm. This will require building place favour the intermediate host Eveni though the capacity of heaIth systems, education, training of there has been a major decrease in prevalence and bealth professionals, community mobilization, and distribution of S japonicum and S. haematobiuim, the information, education, and communication (LEC) bulk of transmission remains in sub-Saharan Africa. activities. Tn Africa the disease is strongly linked with , Success calls for a well-coordinated interna- movement of populations, contamination of water. tional effort to ensure that scarce resourccs are not and agricultural practices. In this continent control wasted, efforts are not duplicated, and planned na- remains a difficult task. The poorest countries where tional programmes are well supported. Clear priori- schistosomiasis is prevalent do not have the eco- ties and a more equitable distribution of resources nomic potential (national or family level) to organize should be made by national governments and by and coordinatc cffective and sustainable disease international and development aid agencies and control. Thus. schistosomiasis is not at present nongoverniental organizations

WHO Bulletin OMS. Vol 76, Suppl 2, 1998 67