Studies on dracunculiasis in the Indian Desert

Vinod Joshi, Manju Singhi & R.C. Chaudhary

Desert Medicine Research Centre (Indian Council of Medical Research),Post Box no. 122, New Pali Road, Jodhpur — 342 005, India

(Received 1 April 1996, accepted 17 January 1997)

Dracunculiasis (infection by the guinea worm, Dracunculus medinensis) hasbeen a major rural waterborne problem in many areas of arid westernRajasthan. The presence of temporary ponds in endemic areas offers apeculiar habitat to cyclops, the vector of the disease. Cyclops can withstanddrying of the ponds and regain viability when ponds refill during rains.Cyclops shows a diurnal cycle of migratory movements under natural as wellas experimental conditions. The species of cyclops acting as intermediate hostin endemic areas is Cyclops atter. This carnivorous species is highly predatoryon the infective first stage larvae of D. medinensis in experimental infectiontrials. Survival of infective guinea worm embryos in free-living form tillingested by vectors is favoured by an alkaline pH of the water.

Measurements of water volume in ponds, removal of soil from dry ponds todiscard cyclops eggs and recording the visit history of guinea worm patientsare suggested as useful additions to an eradication programme againstdracunculiasis. Literature concerning epidemiological, vector-biological, andparasitological aspects of dracunculiasis as relevant to desert districts ofRajasthan is reviewed.

©1997 Academic Press Limited

Keywords: dracunculiasis; Cyclops spp.; Dracunculus spp.; Rajasthan

Introduction

Guinea worm disease caused by the nematode parasite Dracunculus medinensis (Muller,1971) is one of the oldest known human parasitic infections causing morbidity tothousands of people in the form of physical incapacitation. At a global level the diseasehas been known since ancient times and a reference is even found in the Bible(Numbers 21:6). ‘Fiery Serpents’ attacking Israelites while crossing the Red Sea arebelieved to be guinea worms (Joshi, 1981). To Indians also, the disease has beenknown for millenia as a reference about it is found in Susrata (Susrata c.1500 BC).Although dracunculiasis is one of the easily preventable parasitic infections it has beena leading rural waterborne problem in many states of India (Stoll, 1947).

Among the different states in India, Rajasthan has been the worst affected by guineaworm disease. According to Singh & Raghavan (1957), out of 5 million people at-riskof developing guinea worm infection in India, over 2 million resided in Rajasthan aloneduring the year of survey. In this State the disease has been confined mainly to its

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north-western and southern regions. In southern Rajasthan where the disease has beenendemic (in Dungarpur, Banswara and Udaipur districts), the major source ofdrinking water is the step-well. With the major emphasis being given to casecontainment as undertaken by the Sanitation Water and Community Health project(Anon, 1994), the simplicity of vector control measures due to the use of step-wellsreduced the incidence to less than 10 cases in these districts during 1993.

Western Rajasthan differs from the southern region in that it comprises the majorportion of the Indian Desert. Owing to water scarcity and arid ecology, the people heredepend heavily on temporary, shallow rainwater ponds for their drinking water. Theseponds form a habitat for the guinea worm vector cyclops. Owing to their irregularshape and depth it is more difficult to calculate the optimum amount of thecyclopsicide Temephos required for eradication of the vector in these ponds than it isfor step-wells. Moreover, the ponds are open on all sides to approach by persons whomay be harbouring guinea worms, and they are shallow in depth causing moresensitivity to light-induced diurnal migration of the cyclops inhabiting them.

In dracunculiasis-affected areas of western Rajasthan, (i.e. Jodhpur, Nagaur andBarmer districts), the Rajasthan Integrated Guinea-worm Eradication Programme(RIGEP) has been functioning since 1991. RIGEP is a multipronged programmeaimed at preventing dracunculiasis, including containment of patients who mightotherwise infect drinking water, extraction of worms and control of cyclops byapplication of Temephos. Although the disease has been declining since 1991,eradication has yet to be achieved, and from January to December 1995 a total of 76cases were reported. It is therefore appropriate to consolidate available knowledgeabout the course of infection in the desert situation to assist the ongoing eradicationprogramme.

The present paper reviews relevant knowledge on epidemiological, vector-biological,parasitological, sociological and preventive aspects of dracunculiasis, and also presentsoriginal work carried out by the authors on these aspects of disease as relevant to aridconditions in the desert.

Observations and discussion

Epidemiological features

There have been very few published studies reporting the incidence of guinea wormdisease in Rajasthan. In the past studies based on hospital records have been publishedfrom Barmer, Jaisalmer and Jalore districts of western Rajasthan (Chopra, 1967),highlighting maximum incidence in Barmer district. Other reports have indicated alower incidence of guinea worm in Jodhpur and Jaisalmer districts (Patnaik & Kapoor,1967). However, of all the districts surveyed by other workers, maximum prevalenceof dracunculiasis was reported from Jodhpur (Tewari, 1968).

A door-to-door survey of the incidence of dracunculiasis in seven desert districts ofRajasthan was conducted during 1979–80 (Joshi, 1981). Various epidemiologicalfeatures pertaining to age, sex, community of host and other parameters like age at firstinfection and reinfection were studied (Johnson & Joshi, 1982a,b). Unlike otherstudies, these surveys were not based on hospital records but on an on-the-spotenquiry of approx. 62,000 human subjects (Joshi, 1981). Johnson & Joshi’s results(1982a,b) concerning epidemiological features were in conformity with those reportedby other workers in different parts of the country (Chopra, 1967; Tewari, 1968;Bildhayia et al., 1969; Reddy et al., 1969; Rao et al., 1979; Ojha & Johri, 1980). Thestudies highlighted the prevalence of the disease in districts of western Rajasthan(Joshi, 1981) with maximum infection prevailing in Jodhpur, Barmer and Nagaurdistricts. It is interesting to note that the districts reported by Joshi (1981) as having

V. JOSHI ET AL. 182

74

GUJRAT

26

72

SIROHI

JALORE (0.04 %)

BARMER (6.0 %)

JAISALMER (4.2 %)

Jaisalmer

JODHPUR (4.5 %)

UDAIPUR

BHILWARA

AJMER

NAGAUR (2.0 %)Nagaur

Bikaner

BIKANER (0.02 %)

CHURU

SIKAR

INDIARajasthan

GANGANAGAR

PALI (0.01 %)Pali

Barmer

PAK

IS

TA

N

N0 40

km00–55–10

Incidence (%)

15–2020–2525–30

10–15

Jodhpur

Jalore

7272 7470

26

maximum incidence of dracunculiasis during 1979–80 (Fig. 1) are the same regions inwestern Rajasthan which still, as recently as 1995, show most patients (RIGEP,Jodhpur, pers. comm.). Thus, in order to exactly estimate the magnitude of the diseaseand to identify areas most prone to infection, a report based on a door-to-door surveywould illuminate the problem in its true sense.

Vector-biological aspects

A number of studies on the vector, cyclops, and on other aspects have described host–parasite interactions. The most important factor determining whether a particularspecies of cyclops will transmit Dracunculus is its predatory habit. It has been reportedthat larger forms of cyclops tend to be carnivorous and smaller species herbivorous(Fryer, 1957).

Of about 18 species of cyclops reported from India (Johnson, 1985) the widelydistributed Cyclops leuckarti and C. hyalinus are reported to act as vectors ofdracunculiasis. In Rajasthan C. leuckarti, C. hyalinus and C. varicans were reported assuitable vector species in an earlier report (Lindberg, 1946). Various species of cyclops

Figure 1. Dracunculiasis in western Rajasthan (1978–80).

DRACUNCULIASIS IN THE INDIAN DESERT 183

that occur in some areas of south Rajasthan and are susceptible towards infectivelarvae of Dracunculus medinensis have been reported (Bapna, 1985). However, in thedesert of western Rajasthan where cyclops inhabit rainwater ponds it has been reportedby Johnson (1985), based on an earlier report (Lindberg, 1946), that C. leuckarti actsas an intermediate host to transmit infection.

A large number of cyclops from the guinea worm-affected villages of Jodhpur andNagaur districts were collected and maintained as a colony by one author (V.J.) during1994. A careful examination of the fifth leg and other organelles of taxonomicimportance (following Edmondson, 1965) revealed that, in contrast to other reports,the species acting here as vector is Cyclops atter (Joshi, 1994). This was the only speciesencountered in this area and no collected specimen resembled the C. leuckartipreviously thought to be present. Cyclops atter is a carnivorous species and being highlypredatory seems likely to be able to transmit the infection from one subject toanother.

Under the arid conditions of western Rajasthan, water in ponds remains availableonly during the 3–4 months of the rainy season. How cyclops withstands dryconditions in the ponds in the absence of water and how they re-establish themselveswhen water returns has been investigated.

Female C. atter containing egg sacs (Fig. 2(a)) as visible to the eye were picked outfrom the laboratory-maintained colony with the help of a dropper. Egg sacs wereseparated from the sides of the cyclops with the help of fine pins under a dissectingmicroscope. Each egg sac was found to contain about 60–64 eggs. Eggs were foundsticking to each other without any common membrane binding them. An individualegg appeared as a double membrane structure showing some superficial cleavages (Fig.2(b)).

The egg sacs were dried completely on glass slides at 32°C in a Biological OxygenDemand incubator for 3 days. Dried egg sacs appeared under the microscope asopaque masses with individual eggs having developed interconnections (Fig. 3(a)).After drying for 3 days in the incubator, water drops were put on these egg sacs andthey were observed continuously under the microscope at room temperature until theeggs developed into nauplius larvae. Eggs developed normal shape and structure andindividual eggs re-developed membranes similar to those observed before drying (Fig.3(b)) about 1 h after introducing water. Some 2–3 h after introducing water naupliuslarvae emerged from these dried eggs. The eggs in dry form were preserved separatelyon glass slides in the laboratory (32°C) as well as in soil samples (at room temperature)for 2 years and the entire experiment demonstrating aestivation of cyclops and theirreactivation as described above has been performed six times.

Since ponds have a concave configuration the water contained in them recedesgradually, ultimately reducing to a central, smaller dry concavity which presumablycontains most of the aestivating cyclops. It is suggested that this portion of the pond,which in the majority of cases in the study area (UNICEF, Rajasthan, pers. comm.)does not exceed 1·5 m diameter, should be dug away. Removal of soil from the centralbottom concavity is suggested as a supplementary method in addition to application ofTemephos and provision of funnel filters to ensure removal of the majority of eggs.

Another important observation made during the course of our investigations wasthat when fresh eggs removed from the live cyclops were put into water at roomtemperature in a cavity block (to observe the time taken by eggs to transform intonauplius larvae when water is continuously present), within 18 h active, free-swimmingnauplius larvae emerged (Fig. 4). Development of nauplius in 2–3 h from dried eggsand in 18 h from water-maintained eggs bears a significance that under naturalconditions after the first rains there will be immediate development of cyclops larvaein a habitat (pond) having withstood drought or having water throughout the year.These larvae are independently capable of transmitting the infective larvae of D.medinensis (Muller, 1971). The control efforts against cyclops, therefore, should be

V. JOSHI ET AL. 184

undertaken immediately after the first rains to check the chances of transmission evenfrom a pond which remained dry before the rains.

Figure 2. (a) Cyclops atter with egg sac; (b) magnified view of eggs ( 3 10 3 40).

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Behavioural studies on cyclops

During field studies made in 1994 it was observed that samples taken from villagerainwater ponds from different zones (dark and illuminated zones) and from differentdepths yield different densities of cyclops (Table 1). These observations indicate apossible light-induced diurnal migration of cyclops in the habitats available in guinea-worm-affected and unaffected areas of Jodhpur and Nagaur districts. To confirm andevaluate such behaviour, studies in the laboratory were conducted imitating the

Figure 3. Dried eggs of Cyclops atter (a) having developed interconnections, and (b) afterrehydration.

V. JOSHI ET AL. 186

conditions of light as available in endemic areas. The following observations wererecorded: (i) When put into a transparent glass jar of 450 mm height, 300 mm lengthand 150 mm breadth containing water, and by making a zone of 225 mm height, 150mm length and 150 mm breadth in the jar darker by wrapping black paper externally,80% of the cyclops migrated towards the darker zone covering a distance of about 240mm in 20 min. The remaining 20% which were not attracted towards the darker zonewere found to dwell at the bottom.

(ii) After dawn, when observed from 0630h to 1030h, cyclops tended to distribute

Figure 4. Nauplius larvae emerging from (a) dried and (b) normal eggs of Cyclops atter.

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Table 1. Distribution of cyclops in village rainwater ponds at different depths and zones

Village Status* District Zone/station Density†

Chadi Affected Jodhpur Illuminated 150Dark 430Surface 75Bottom 1600

Kudi Unaffected Jodhpur Illuminated 69Dark 181Surface 25Bottom 429

Tantwas Affected Nagaur Illuminated 7Dark 16Surface 2Bottom 39

Tankla Unaffected Nagaur Illuminated 32Dark 129Surface 15Bottom 213

*Village affected by dracunculiasis or not.†Number of cyclops filtered from 360 l of water.

throughout all the dimensions of the glass jar and afterwards preferred to migratetowards the bottom.

(iii) When the entire glass jar was made dark, cyclops were found uniformly at allpoints.

There have been very few studies on the behaviour of cyclops, and almost none onthis aspect, that are relevant to habitats of western Rajasthan. Onabimaro (1951)reported that in some African villages cyclops infected with larvae of D. medinensis tendto migrate to the bottom of the ponds. Field observations in arid parts of Rajasthanreported in this paper reveal a light-induced diurnal migration tendency of cyclopswhich would help to locate the maximum density of cyclops at a particular point in apond during particular hours of the day. Hence in view of these observations, careshould be taken when applying Temephos. It has also been recommended (NationalInstitute of Communicable Diseases, 1983) that species of cyclops, volume of water tobe treated and local conditions should determine the frequency of application ofTemephos (Bapna, 1985). Our observations would thus specify that the controloperations against cyclops should be adapted to the local conditions affecting thevector and its habitats in arid areas.

Parasitological aspects and host–parasite interactions

Infection of cyclops by freshly emerged first stage larvae of D. medinensis would dependon density of cyclops and of larvae available in a given water volume. Our laboratorystudies revealed that when a drop of guinea worm discharge from a patient is placedinto about 500 ml of water in a beaker, infective first stage larvae are uniformlydistributed throughout the volume of water. Therefore, under natural conditions, theconcentration of these larvae at a given point would depend on the amount ofdischarge by a patient and the volume of water. Survival of infective larvae in their free-

V. JOSHI ET AL. 188

living form until ingestion by the vector cyclops has been studied by Joshi (1992) whoreported that an alkaline pH was more favourable for their independent survival for upto 72 h. However, after 72 h of free-living existence the larvae died, and their infectivity(in terms of pronounced development of cephalic structure within the cyclops)declined after only 12 h of free-living existence and very few of them could be seenalive in the cyclops’ body.

Experimental infections of cyclops with guinea worm larvae have been attempted bymany workers in India (Moorthy & Sweet, 1936; Lindberg, 1946; Rao & Reddy,1965). In Rajasthan C. leuckarti, C. hyalinus and C. varicans have been experimentallyinfected and found susceptible to infective guinea worm larvae (Lindberg, 1946).However, C. atter has not been studied so far from this aspect but we have found it avery convenient species to be infected experimentally. On average the species ingested2–3 larvae in experimental conditions and was found to be highly predatory.Development of the parasite within the cyclops was observed by inactivation at 4°Cimmediately prior to microscopic observations. After approx. 12 days at roomtemperature larvae within the cyclops were observed to develop a pronounced cephalicstructure, and to penetrate the gut wall and become active in the cyclops’haemocoel.

In agreement with the report of Onabimaro (1951), in our studies the infectedcyclops settled at the bottom of an experimental jar and became active only when thebottom was stirred. Attempts to infect other zooplankton found as co-fauna withcyclops, i.e. Daphnia and diatoms, were not successful.

Sociological aspects in communicability of the disease

In desert areas of Rajasthan, people make relatively more visits during the rainy seasonto maintain their social relationships than during the dry season. Since it is during therains that infection is most readily transmitted from infected subjects through ponds toother subjects this has an important bearing on the transmission of disease. Since 1991it has been regularly observed in Jodhpur district (RIGEP, Jodhpur, pers. comm.) thateach year a different village emerges as having the maximum number of guinea wormpatients. From 1992 to 1995 the villages having the maximum incidence were, in turn,Bapini in Osiyan tehsil, Salva kala in Jodhpur tehsil and Chadi and Jakhen in Phaloditehsil (RIGEP, Jodhpur, pers. comm.). Consequently, in the preceeding year we neverknow which village will next have the highest incidence of the disease but at the sametime one has to apply measures to control cyclops 1 year in advance.

To begin control operations on cyclops 1 year before the expected appearance of thedisease in a particular village, we have to identify which villages can possibly beaffected in the next year. It is therefore suggested that while adopting a village forcuring guinea worm patients and applying Temephos for control of cyclops we recordthe names of dracunculiasis patients and their demographic details. These patients canbe interviewed using a questionnaire which focuses mainly on the places they havevisited while harbouring active infection of D. medinensis. Places visited by the patientsshould be recorded so that control operations can be undertaken there at the same timeas in villages which had incidence of disease in the current year. It should be kept inmind that control operations against dracunculiasis undertaken during a particularperiod will have an impact on the outcome of the disease during the next year.

Suggestions relevant to desert conditions

Dracunculiasis has declined since the Rajasthan Integrated Guinea worm EradicationProgramme has intensified its efforts (Table 2) to stamp out the disease from arid areas

DRACUNCULIASIS IN THE INDIAN DESERT 189

Table 2. Dracunculiasis in western Rajasthan in 1993–95*

No. of guinea worm cases No. of affected villages

District 1993 1994 1995 1993 1994

Jodhpur 466 190 36 80 34Nagaur 141 146 28 49 40Barmer 24 13 0 8 6Bikaner 30 85 12 9 13

*Data obtained from RIGEP, Jodhpur.

of Rajasthan. However, since the disease has a long incubation period, infected waterexists as temporary shallow ponds and the population in the desert area is scattered inpockets, ongoing control operations can incorporate the desert-specific researchobservations made here to achieve the target of eradication. The following suggestionsare therefore made: (1) The area of ponds is measured by conventional methods.However, the depth of a pond varies at different points due to its concavity. Pillarsmarked at 300 mm intervals can be implanted at the centre of the pond and at twopoints nearer the margin while the ponds are dry. This will allow the volume of waterpresent to be measured with better accuracy at a particular time and the quantity ofTemephos required can be worked out accordingly.

(2) Since cyclops concentrate towards the bottom for some hours of the day and alsosince infected cyclops always prefer the bottom, Temephos should also be applied tothe bottom using a suitable pumping device.

(3) During the dry season up to 150 mm of soil can be removed from the centralconcave part of dry ponds to discard the majority of deposited eggs. Soil so removedshould be deposited at a safe place so that during rains it is not leached by waterflowing to the pond. This may be observed as an additional measure only whereapplication of Temephos and provision of funnel filters alone have not producedsuccessful control as in some affected villages of Rajasthan (RIGEP, UNICEF,Rajasthan, pers. comm.).

(4) As nauplius larvae develop within 24 h of first rains, control efforts againstvectors must be undertaken immediately after the first rains fall in the area to rule outthe chances of transmission.

(5) Movements of guinea worm patients during the transmission period should berecorded and villages visited by patients should be subjected to control operationssimultaneously with currently affected villages.

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