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Previous Article | Next Article 
Clinical Microbiology Reviews, April 2002, p. 223-246, Vol. 15, No. 2
0893-8512/02/$04.00+0 DOI: 10.1128/CMR.15.2.223-246.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom,,1 Department of Control, Prevention and Eradication of Communicable Diseases, World Health Organization, Geneva, Switzerland2
SUMMARY INTRODUCTION BIOLOGY OF THE DISEASE Morphology Life Cycle Zoonotic Aspects CLINICAL ASPECTS Clinical Manifestations and Pathogenesis Diagnosis Treatment SOCIOECONOMIC IMPACT Disability Economic Impact Nutrition, Education, and Perpetual Benefits EPIDEMIOLOGY Water Sources Villages of Endemicity Seasonality Individual Risk Factors THE ERADICATION INITIATIVE INTERVENTIONS Safe Water Supply Filtration of Drinking Water Case Management Preventing Patients' Contact with Ponds Killing or Removing Cyclops Case Containment Intervention Conclusions CURRENT ISSUES The Integration Debate Geographic Information Systems (GIS) The Certification of Dracunculiasis Eradication Concluding Remarks ACKNOWLEDGMENTS REFERENCES
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| INTRODUCTION |
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Connection of infection with water sources was recognized early, and it is probable that, if the prepatent period were not so long, the mode of infection would have been obvious many centuries earlier. As it was, this was determined in 1870 by a Russian naturalist, Alexei Fedchenko (67), who found that larvae expelled from emerging female worms in the limbs of sufferers developed in freshwater microcrustaceans (cyclops) living in ponds, which were then ingested in drinking water.
In historical times infection occurred in Algeria, Egypt (162), Gambia, Guinea Conakry, Iraq, Brazil, and the West Indies (163) but died out spontaneously in those countries and was eliminated from Uzbekistan in 1932 and from southern Iran in 1972.
| BIOLOGY OF THE DISEASE |
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The same or similar species of Dracunculus have been reported sporadically for mammals and reptiles (snakes and turtles) in many parts of the world (116); species from birds have been separated into a different genus, Avioserpens.
A mature female D. medinensis is one of the longest nematodes, measuring up to 100 cm, but is only 1 to 2 mm wide (Fig. 1). The vulva is halfway down the body. In filarial females the microfilarial prelarvae emerge from this opening throughout the life of the worm. In Dracunculus, however, it is closed with a plug, and the whole body cavity is filled with the uterus, which extends anteriorly and posteriorly and contains from 1 to 3 million first-stage larvae. The gut is also completely flattened and is nonfunctional. Bright red worms have been reported from Pakistan (56), but their significance is not known. Males have been recovered only doubtfully from humans, but those from experimental animals measure 15 to 40 by 0.4 mm; the tail has three to six preanal and four to six pairs of postanal papillae, with subequal spicules (490 to 750 µm long) and an accessory organ, the gubernaculum (about 117 µm).
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For further development, the larvae need to be ingested by suitable predatory species of copepods, measuring 1 to 2 mm. Until a few years ago, these were all included in the single genus Cyclops, but this has now been subdivided, and the most important intermediate hosts belong to the genera Mesocyclops (M. aequatorialis and M. kieferi), Metacyclops (M. margaretae), and Thermocyclops (T. crassus, T. incisus, T. inopinus, and T. oblongatus) (119). Larvae develop to the infective third stage in the body cavity in 14 days at 26°C. For further development of the larva, the host copepod needs to be ingested in drinking water obtained from ponds or open wells. Once in the human body, larvae are released in the stomach and migrate through the intestinal wall, across the peritoneal cavity, and into the wall of the abdomen and thorax by 15 days (Fig. 2). After two molts the sexually mature males and females meet and mate in about 100 days, while they are both of comparable size. The males remain in the tissues and in a few months become encapsulated and die. In experimental infections by Dracunculus insignis in ferrets, males can live for at least 330 days (19) and therefore are potentially able to fertilize females for another year. The females move down the muscle planes and by 10 months have grown greatly, with the uterus being filled with larvae. They emerge about 1 year after infection, usually from the feet and lower legs (Fig. 3) but occasionally from any other part of the body.
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Table 1 lists the species of Dracunculus which have been reported. Emerging female worms are recovered sporadically from a wide range of mammals both from parts of the world where dracunculiasis is endemic and from parts where it is not (12, 49, 69, 71, 89, 90, 103, 106, 110, 135, 140; review in reference 116). Unfortunately, in almost all cases only a portion of a female worm is recovered, usually in a flaccid state after the enclosed larvae have been ejected, and identification with regard to species is impossible. In general, worms in mammals are regarded as D. medinensis in the Old World and South America and as D. insignis in North America. Dracunculus has a very short patent period, at the most a few weeks, and an emerging worm is not easy to see in fur-bearing carnivores (Fig. 4), so it is likely that infection is much more common in many countries than is currently recognized. This is well illustrated by the situation in North America, where there are one or two reports of infection in wild carnivores and domestic dogs each year, mostly from states in the southeastern United States and from southern Ontario, Canada (e.g., see reference 14). However, in studies where large numbers of raccoons were dissected and immature worms were found, prevalence rates of 13.8% (144) to about 50% (47) were recorded.
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An isolated autochthonous human case of dracunculiasis has been reported from Japan (105), and similar older cases occurred in Korea (76) and Indonesia (157). In all of these presumably zoonotic cases, there was the possibility that infection was contracted from ingesting raw freshwater fishes as paratenic hosts (in which the immature parasites ingested in cyclops can survive but do not develop) rather than from drinking water: certainly Dracunculus in North America can be transmitted experimentally by amphibians (47, 54). Experimentally, rodents can be infected with larvae of the human parasite, which can live for months in the peritoneal cavity without development, and these could act as paratenic hosts for infections in carnivores (R. Muller, unpublished data). Infections in reptiles appear to be due to separate species (see reference 116).
The infections in domestic animals reported from areas of endemicity are possibly of human origin. This supposition is supported by the higher prevalence found by surveys of the human population than by the dissection of dogs culled during the 1920s in Bukhara, Uzbekistan (Fig. 5). However, worms are still found in dogs in the former areas of endemicity of Uzbekistan (99) and Tamil Nadu (106) and also in dogs and cats in the areas of Azerbaijan, Kazakhstan, and possibly Turkmenia where the disease is not endemic (44, 45, 71, 110, 158). It is very likely that in many parts of the world there are widespread but underreported animal cycles completely independent of human infection: for example, there was a recent report from China of infection with D. medinensis in a cat (69). It is significant that the disease has not returned to Uzbekistan in the 70 years since it was eliminated there, in spite of the fact that about 40% of the rural population still does not have piped water and only 33% in the area surrounding Bukhara, the historic focus (171), have piped water. Nor has it returned to Egypt, Iran, Gambia, or Guinea, where it disappeared decades ago.
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| CLINICAL ASPECTS |
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Dracunculiasis is unusual among parasitic infections in that there is little evidence of acquired immunity and the same individual can be reinfected many times. The response to the extrusion of larvae is indicative of an Arthus reaction followed by a delayed hypersensitivity response (117).
| SOCIOECONOMIC IMPACT |
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In the past, most cases of dracunculiasis went unreported for a number of reasons: most health centers had little to offer the patient besides palliative treatment; most patients live in poor, remote rural areas and are hindered by their disease from walking to a health facility; and most recover spontaneously after expulsion of the worm. For example, a large teaching hospital in Nigeria never saw dracunculiasis cases in the Casualty Department, although the disease was endemic in villages a few kilometers away. Because few cases were reported, the disease was often considered an exotic curiosity rather than a major public health problem. However, in areas of endemicity its social, economic, nutritional, and educational consequences, and the costs incurred by the individuals, households, and communities which suffer from it, can be substantial.
The social impact of guinea worm disease is mainly attributable to the temporary disability suffered by the patient. Two longitudinal studies in Nigeria (5, 143) found that 58 to 76% of patients were unable to leave their beds for approximately a month during and after emergence of the worm. The more severe and protracted disability is associated with secondary infection of the lesion; this occurs in roughly half the cases (124, 184).
The impact of this temporary disability is reinforced by the seasonal pattern of worm emergence, often peaking at stages of the agricultural year when labor is in maximum demand. This is illustrated in Fig. 6, where the topmost section shows the seasonal variation in agricultural activity in northern Burkina Faso, peaking with the sowing season in June. The middle section shows the corresponding variation in cases of dracunculiasis, also peaking in June. The pattern typical of the forest zone to the south is shown in the bottom section of Fig. 6; here cases peak in the dry season, but this is the time for yam and rice harvesting (143). This seasonality means that a whole community can be laid prostrate simultaneously and household members can be prevented from substituting for one another in agricultural and other tasks (13). Indeed, it has been claimed that the effect of the disease on agricultural productivity can be detected in satellite photographs (6). The Dogon people of Mali refer to the infection as "the disease of the empty granary" (172).
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It has been argued previously that this method of calculation uses an oversimplified approach and is likely to overestimate the cost (75, 128), as it does not allow for the various coping strategies by which households respond to illness (such as abandoning other tasks and using additional labor), which qualitative studies have found to be common in peasant farming (23, 38). A more sophisticated approach is to examine the impact on actual production (24) or even to include the incidence and duration of dracunculiasis-induced disability as predictive variables in an agricultural production function. Audibert (9) used this approach, in a setting in northeastern Mali where the incidence of guinea worm disease was "relatively low" (between 3 and 33% in the villages studied), to show that temporary disability accounted for a reduction of 5% in the overall production of two important subsistence crops: sorghum, mainly grown by men, and peanuts, cultivated by women.
However, there is also a cost to the coping strategies, which cannot be measured using this approach. Mutual assistance (164) simply transfers the cost of the disease to other households and is of little help to wage laborers (36). The simplistic approach used for the Nigerian study mentioned above may be more accurate than it seems.
Children also suffer in other ways from guinea worm disease in their families. Children miss school when they have guinea worm (in rural Africa, school is usually a long walk away) and also when they have to substitute for their ill parents in doing agricultural work and other household tasks. As a result, school attendance suffers during the peak season (22, 60, 62, 92, 124), and schools in areas of endemicity often have to close for 1 month in each year as a result.
Guinea worm disease is of special interest to economists not only because of its direct and measurable impact on production but also because of the singular ability of disease eradication to produce a perpetual stream of benefits at no ongoing cost. It is, therefore, surprising that a recent cost-benefit analysis of the eradication effort by the World Bank (104) considers only the benefits from incidence reduction during the campaign; their estimate of a 29% economic rate of return for the global campaign, which they estimate to have cost some $90 million to date, is certainly pessimistic.
| EPIDEMIOLOGY |
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Numerous studies have illustrated the predominant role of ponds in dracunculiasis transmission in various parts of Nigeria (57, 58, 59, 60, 61, 100, 127), Ghana (112, 138), Burkina Faso (70), Togo (129), Uganda (77), Pakistan (86), India (98), and what is now Uzbekistan (171).
Many (probably most) of the ponds involved in transmission are human-made. Table 2 shows the findings of Steib and Mayer (147) for a village in Northeast Burkina Faso, which illustrate the large number of ponds which can be found in a single village, even in a semiarid, Sahelian setting, and the degree to which relatively few human-made ponds, with specific characteristics, play a significant role in transmission.
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Outbreaks of guinea worm disease have occasionally been blamed on the construction of large dams (3, 59). However, their role in transmission has usually resulted from the use of ponds left by the receding water during drawdown of the water level.
Various types of wells and storage tanks can become sources of the disease. Rectangular masonry-lined step wells were the principal sources of infection in Rajasthan, India (142), and shallow wells have been implicated in Mali (130). Scoop wells dug in sandy riverbeds can also be a source, although if these water holes are exhausted by the drawing of water each day, no cyclops population can be sustained in them, and so transmission cannot occur (31). In Iran, the "berkeh" (traditional covered water storage cisterns with a diameter of over 10 m) were implicated (137).
Transmission has also occurred from rainwater storage reservoirs used by individual households, such as the "karkour" of the Nuba Mountains of Sudan (31) and in an isolated incident in 1993 in El Rohaibat, Libya, from a buried reservoir filled from a farm tank which an infected migrant worker had contaminated (102). Relatively few cases are caused in this way, because there must be an index case in the household to contaminate the reservoir, but when they do occur, transmission is more intense than usual because the infected cyclops are contained in a smaller volume of water, and this is reflected in a higher average number of worms per patient (32).
Two broad patterns of seasonality are found in the African areas of endemicity, depending on climatic factors. In some countries, both patterns occur, each in a different climatic zone (Table 3). To the north in the Sahelian zone, transmission of dracunculiasis is generally limited to the rainy season from May to August with a peak in June and July (73). Steib and Mayer (147) attributed this pattern to the presence of T. inopinus in the surface and shallow water used for drinking; however, others have found it more difficult to correlate occurrence of cyclopoids in the local water sources with the prevalence of infection among the people using them (185). More fundamentally, many water sources involved dry up and hand pumps are repaired in the dry season, so that the population turns to safer groundwater sources (48).
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There are local variations in these patterns. The duration and intensity of transmission in particular villages often depend on whether and when the local dams or ponds dried up the previous year (152), and some villages have very different seasonal peaks from those of the surrounding area because of local circumstances. For example, in some villages along the banks of the Niger and Volta rivers the incidence peaks when the river level falls and water is taken from holes dug in the riverbed.
For example, a significantly higher prevalence has been found in women in Ethiopia (97) and in men in India (98) and sometimes in West Africa (3, 39, 123); however, when behavioral risk factors (such as work in the fields or collection of water) are taken into account, the difference between the sexes is not significant (153).
Two possible age prevalence profiles are illustrated in Fig. 7. The graph for four high-prevalence villages, each with an infected water source, shows similar prevalences in children and in adults. The remaining 23 villages in the study area show a lower prevalence in all ages but significantly less in children than in adults. The former is characteristic of communities where the water carried home is infected, while the latter is indicative of an association with mobility, where infection is acquired from water sources outside the community.
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| THE ERADICATION INITIATIVE |
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The suggestion that dracunculiasis might be eradicable fell on fertile ground. Smallpox had been eradicated in 1977, and some of those associated with that achievement were looking for a suitable candidate to adopt for the sequel (7, 78, 141), while taking care to avoid a mistake like the targeting of malaria in 1955 (109). Another possible candidate was poliomyelitis, and indeed some of those involved in guinea worm eradication have seen it as a rehearsal for the eradication of polio, particularly in the difficult African terrain where the last cases of both diseases will probably occur. Table 4 compares the prospects of all four diseases in the eradication stakes.
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This advocacy effort needed to be replicated in each country to get a national program established (64). In 1982, India was the first to initiate a national eradication campaign. By 1990, four other countries had followed: Pakistan, Ghana, Nigeria, and Cameroon. In the following 5 years, all the other known countries of endemicity also established national eradication programs, and substantial and progressive reductions in disease incidence were recorded each year, particularly at the beginning of the campaign (Fig. 8a and b).
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An important means to this end has been the series of regional conferences and meetings of national program coordinators, together with program review meetings at which each national coordinator would give a presentation on her or his program and then answer a barrage of penetrating questions from her or his skeptical colleagues from neighboring countries. Donor involvement and coordination were also supported by regular interagency meetings, usually held in the United States or Africa and attended by representatives of the Carter Center, UNICEF, the U.S. Agency for International Development, the World Bank, WHO, and other agencies. High-level advocacy was also supported by the continuing involvement of Jimmy Carter and two African former heads of state whom he persuaded to play a similar role, A. T. Touré of Mali and Yakubu Gowon of Nigeria.
The principal international stakeholders in the program have been relatively few in number: the Carter Center, UNICEF, the World Bank, and WHO. Other major supporters, such as the Bill and Melinda Gates Foundation and the British and Japanese bilateral aid programs, have usually channeled their funding through these agencies. The major players liaise periodically to identify major gaps in the funding of national programs, and in most countries of endemicity, one or another of them has, by consensus, taken the leading role. From 1992 to 1996, when national eradication programs were being established, UNICEF and WHO maintained a joint technical team based in Ouagadougou, Burkina Faso, to provide technical support to national program coordinators in the region and to external support agencies; the Carter Center also seconded one of its staff to this team in 1994.
The outcome of all this effort has been a remarkable 98% reduction in the number of cases, from an estimated 3.3 million worldwide in 1986 (161) to only 75,223 cases reported in 2000. Only 14 countries, all in Africa, reported indigenous cases in 2000 (180).
| INTERVENTIONS |
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Given the transmission cycle of the parasite and the absence of an effective vaccine, a number of interventions would seem a priori to be worth considering: (i) provision of a safe water supply, (ii) filtration of one's drinking water to remove cyclops, (iii) searching for patients with active cases and proper management of cases, (iv) ensuring that patients avoid contact with ponds, and (v) killing or removing cyclops in ponds. These are considered in turn.
There is plenty of evidence for the impact of water supplies on dracunculiasis (15, 31, 62, 77, 98, 112, 133, 156). Table 5 provides a summary; all the impacts reported there were assessed after at least a year and in one case (62) after 3 years. India's rural water supply program gave priority to villages of endemicity and, by the time that the national eradication program was concluded, had provided a supply to every village of endemicity in the country. This was an important contribution to that country's successful elimination of the disease in 1997. However, there are also some important limitations to the effectiveness of water supply as a preventive intervention.
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In the 1970s, the Ivory Coast was in the vanguard of African countries providing rural water supplies. Between 1973 and 1985, a total of 12,500 new boreholes were installed in rural areas, at a cost of many millions of dollars. As a result, the annual number of cases of guinea worm disease fell from 67,123 in 1966 to only 1,889 in 1985 (165). In 1991, however the national case search found an estimated 12,690 cases (134). The case enumeration methods may not have been exactly comparable, but the main reason behind this recrudescence of cases became clear in 1992 when UNICEF carried out a survey of hand pumps in three of the subprefectures of highest endemicity of the country and found that more than half of them were out of order, in spite of a recently concluded hand pump rehabilitation project in the area. Since then, hand pump maintenance has much improved, and the incidence of dracunculiasis has fallen sharply, with only 467 cases reported during 1999.
The second limitation is that provision of water supply to every village and hamlet is not always feasible. In the Benin project mentioned above, the prevalence of guinea worm disease in villages of endemicity with fewer than 150 inhabitants was four times that in the largest villages (154), but they were specifically excluded from the borehole program as they were considered too small to justify the cost of drilling and to maintain a hand pump sustainably (186).
Third, a functioning water supply will still be ineffective if it is not used. The most common cause of nonuse is that the supply is not close enough to people's homes. In the countries of endemicity of the Sahel, a hand pump may be the only source of water for miles around in the dry season; however, guinea worm transmission peaks during the rains, when people are often infected from the many ephemeral ponds which are within a few hundred yards of their houses. In southern Sanmatenga Province, one of the major foci of guinea worm disease in Burkina Faso, there is a working hand pump for every 600 people, but for more than 1 household in 10 that pump is more than 1 km away.
Fourth, much of the population in the rural Sahel migrates. In addition to the movement of the nomadic pastoral population, it is common practice in countries such as Burkina Faso and Niger for a village to disperse during the growing season (which is also the peak dracunculiasis transmission season) to a number of small and seasonally occupied hamlets, some of which may be in other districts, or even to sow their crops in several different areas and tend those where the region's unpredictable rainfall turns out to be most plentiful. When a borehole can cost as much as $10,000, it is not a cost-effective option to provide one for every such hamlet.
Fifth, water supplies alone cannot eliminate dracunculiasis if they are not used exclusively. Guinea worm infection is often acquired through casual use of unprotected sources when people are away from home, especially when they are working in the fields. This is confirmed by the common finding that adults, particularly farmers, are more commonly infected than are children (13, 31) and that people traveling away from their village are at greater risk (153).
Finally, water supplies are expensive. Typical rural water supplies in sub-Saharan Africa have a median capital cost of over $40 per person served (167), with an additional recurrent maintenance cost; while the maintenance costs are probably comparable with the recurrent costs of delivering other interventions, the capital cost is an order of magnitude greater.
This does not mean that water supply has no role to play; in some cases, particularly in the few urban foci of dracunculiasis, it has been decisive. However, its impact must be assessed realistically. It can be seen as transforming a high-prevalence community where all water is contaminated (like the four villages in Fig. 7) to a low-prevalence community where only those who use unprotected sources are at risk (like the 23 villages in Fig. 7).
As the national eradication programs took shape during the early 1990s, it became clear that they would rely largely on health education to promote the use of cloth filters. The initial evidence base for this emphasis was little more than the experience of three villages in Burkina Faso (70). However, the strategies of a number of successful public health initiatives in the past have been based on debatable evidence or worked out only during implementation; for example, there were cogent arguments at the outset of the Onchocerciasis Control Program that it would fail (H. Disney, personal communication), and the "search and contain" strategy which successfully eradicated smallpox was discovered only when the campaign was already under way (68). Perhaps the decisive argument in favor of health education was the fact that this was something which ministries of health could do without having to mobilize the support of other ministries (such as water) or hefty financial resources.
Fortunately, the filtering of water builds on existing practices in the region of endemicity, as cloth or sieves are widely used in Africa to filter various liquids. Early eradication programs distributed cotton cloth, but this was sometimes used as clothing or for decoration, and homemakers also complained that it soon became clogged with the sediment in the water so that too much time was needed to do the family's filtering.
An important additional step to successfully inducing behavior change was, therefore, the introduction of the right type of filter cloth. In the early 1990s, the cotton cloth was replaced by a monofilament nylon cloth, which was donated in huge quantities by Precision Fabrics Group through the Carter Center and which is less susceptible to clogging (53). More recently, a somewhat cheaper polyester fabric has been found to be equally effective and acceptable (125). These filters have proved so popular that many households have bought them and filtered their water with them whether or not they have heard that it can prevent guinea worm disease.
Several hundred thousand square meters of this cloth were donated during the 1990s; at the sale price of the fabric, this represents a donation of over $14 million (33). A study in Pakistan (93) found the filters in satisfactory condition after 12 to 15 months of use. Unfortunately, it gradually became clear that in Africa the cloth could not be expected to last for more than a year, particularly when people washed it regularly, with the vigor that they customarily used on other items of domestic laundry. This meant that filters had to be replaced regularly. Since the ending of the fabric donation program in 1998, the national programs have had to distribute cotton cloth or to find the funding to purchase monofilament fabric at some $4 per square meter. The cost of the cloth has encouraged national programs to find more economical ways of using it, such as stitching a patch of it into a hole in a larger piece of ordinary cotton baft (35).
One particularly cost-effective use of the material is to fix it over the end of a piece of 10- to 20-mm-diameter plastic pipe, 100 to 200 mm long. This "straw" filter can then be taken on journeys or to the fields and used to drink from ponds. A hole can be drilled through the pipe so that it can hang around the neck from a string. First introduced with success by the Mauritanian program, it has also been used in Niger and in southern Sudan.
When the nylon cloth was being donated, some national programs, such as those of Burkina Faso and Togo, sold the filters for a nominal sum. This was to help pay for the cost of making up the cloth into a handy form and also seen as ensuring that those who acquired the filters would value them. During Togo's general strike in the mid-1990s, the revenue from sale of filters kept health workers motivated and active in the eradication program when no other government programs were functioning. However, not every household chose to buy a filter. An evaluation of Burkina Faso's program in 1994 found that only 59% of households in villages of endemicity had acquired filters; the constraint was not in the distribution system, as some filters had reached all but 3 of the 31 villages surveyed (S. Cairncross, unpublished data). Ironically, now that the national programs have to purchase the filter cloth, all of them have decided to distribute filters free of charge in communities of endemicity, with a view to ensuring complete coverage.
Evidence of the effectiveness of this treatment, particularly in the final stages of a local campaign to eliminate dracunculiasis, is provided in Fig. 9, showing the decline in cases in the three districts where Sharma practiced, by comparison with the other districts of endemicity of Rajasthan, India.
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A more widely used form of case management is to apply an occlusive bandage to the lesion where the worm is emerging. This does not prevent the release of larvae into the environment, but it does discourage the patient from immersing the affected part in a pond; immersion transforms a neat bandage into a soggy mass of wet cotton wool, which is likely to fall off. Coupled with other palliative treatments by the village health worker, such as "controlled immersion" of the lesion in a bucket of water, disinfection of the lesion, topical application of emollient creams, and even antibiotic ointment (166), bandaging by a village health worker has been used to promote early self-reporting of cases.
In the early stages of the worldwide eradication campaign, however, such measures were ruled out as impractical in a rural context where case detection within even a month of emergence could be considered an impressive achievement. Instead, the message that patients should not contaminate ponds was usually a secondary message in the general health education materials. As a result, people were far more aware of how one catches the disease than of how one passes it on. For example, an evaluation survey of 26 villages in Niger in 1994 showed that, while 54% of householders knew that dracunculiasis is transmitted in drinking water, only 13% could say how ponds become infected with it (26).
More recently, it has become clear that people sometimes respond so well to this message that it can have a significant effect on transmission in the complete absence of filter cloth. For example, in an area of some 160 villages in Adior District in Bahr el Ghazal Province, Sudan, in 1999, not enough cloth filters were available, so that only 44% of households had one. Nevertheless, a reduction of 88% in the number of cases was achieved, with only 515 cases reported in the first 10 months of 2000 compared with 4,177 in the same period in 1999. The prevention of pond contamination by patients was a major feature of the 4,304 health education sessions performed by village volunteers during 1999, following a training course developed by WHO and the Carter Center in collaboration with the nongovernmental organizations (NGOs) operating locally and the Sudan Ministry of Health.
In more recent times, temephos, an organophosphate insecticide safe for use in drinking water sources, has been used in many countries of endemicity, and $2 million worth has been donated to the campaign by its manufacturers (33). Cyclopicide played a prominent role in the eradication programs launched in the 1980s in India, Pakistan, and Cameroon. All these programs have successfully achieved elimination, but this took many years (Fig. 8c). Did vector control help?
In Africa, vector control has not proved as easy as initially anticipated, in spite of there being fewer ponds per person than there were step wells in India. Chemical treatment of African ponds, even by highly qualified research teams, has been found on a number of occasions to be of questionable effectiveness 74, 148; O. Doumbo, personal communication). When the treatment is not fully effective, there is an increased risk of cyclops developing resistance to the cyclopicide. Even treatment which successfully removes the cyclops from the pond does not always eliminate guinea worm disease, as other contaminated water sources are often in use (40, 113).
Transmission is most intense in ponds which are in the final stages of drying up (13, 152) and which therefore may be missed by the treatment team. This is because the infected cyclops, which tend to sink to the bottom (122, 126), are increasingly likely to be scooped up as the pond becomes a shallow puddle.
Treatment of ponds can also consume substantial resources, particularly in terms of trained staff. It is harder to calculate the volume of an irregular pond than of a rectangular Indian step well, although this is essential in order to estimate the dose of insecticide required (34). Given the difficulty, it is impressive that local health technicians have demonstrated on training courses that they can measure pond volumes to within ±10% (A. Maïiga, personal communication). However, it usually takes them the best part of half a day to do so.
Moreover, the pond volume varies with time; if rainfall after the treatment does not dilute the insecticide to harmless levels, the pond may still need to be remeasured the following month, although a solution used in India to avoid continual remeasurement of the volume is to insert a calibrated scale in the pond. Treatment has to be applied at least monthly to be effective, and there is evidence to suggest that an even shorter treatment interval is required (40). With as many as 10 ponds to treat per village (Table 2), it becomes a very labor-intensive activity. There is some evidence that it has diverted staff from other, more important activities (26).
As always, there are exceptions. In 1997, the eradication program staff in northern Ghana found that most of their cases came from only four district towns, each of which used water from a dam. The dams were nearly 10 times the maximum size recommended for treatment (34). Nevertheless, after some experimentation, they found that cyclopicide could be applied very effectively to these (28)
If this is to be effective, it requires detection of each case before or immediately after the emergence of the worm and measures to ensure that it could give rise to no subsequent case. Controlled immersion and bandaging, as described above, help to encourage self-reporting of cases, essential if the cases are to be detected in time, and also discourage patients from immersing their lesions in water. Patients and their families are urged to keep out of water sources until the worms have completely emerged and are also interviewed to ascertain whether they have already contaminated any ponds. If so, remedial measures are taken, such as alerting the community to this possibility, treatment of the affected ponds with cyclopicide, and checking that every household in the village has a cloth filter in good condition and knows how to use it. To ensure the effective implementation of case containment, each case should be reported to the supervisor of the village health worker within 7 days, and the supervisor should visit to verify the diagnosis and ensure that all necessary measures have been taken.
These measures require substantial additional resources (72): the cost per village is probably at least double the cost of the conventional approach (29). Some of the principal international agencies involved expressed concern that these resources should be deployed effectively, so in 1994 a meeting was organized in Nairobi, Kenya, at which technical standards for effective case containment were defined and agreed on (8). According to these criteria, a case is considered to have been successfully contained only if (i) it was detected before or within 24 h of worm emergence; (ii) the patient has not entered any water source since the worm emerged, or if so, the source has been treated in time to prevent transmission; (iii) the case has been properly managed by cleaning and bandaging until the worm(s) is fully removed, and the patient has been discouraged from contaminating any water source; and (iv) the diagnosis and the containment of the case have been verified by a supervisor within 7 days of worm emergence.
It followed from this that eradication programs where the resources did not permit a supervisor to visit each village of endemicity more than once a month could not be considered to be implementing case containment, even if the village health worker did carry out some containment activities; the Nairobi participants referred to this as "intensified case management." Table 6 shows the conditions required for effective implementation of eradication activities at these two levels of intensity. It has taken several years for all the countries of endemicity to adopt these standards; for example, Niger maintained that a case had been contained if the case was detected in a week, coming into line with other countries only in 2000. Even now, a number of countries do not confirm the diagnosis and containment within a week.
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