ern Bangladesh in late 1992, and bythe end of March 1993 over 107 000cases of severe diarrhoea and 1473deaths had been reported.

Cholera is generally understood tobe transmitted by the faecal-oral route,that is from the faeces of an infectedindividual, then through water, food,or other means to the mouth of a new,susceptible individual. The means toprevent such transmissions are wellunderstood, yet cholera epidemics con-tinue to flourish. Why is this so? Inpart, it is because of high populationgrowth, high population density, andpoverty, and it occurs where waterservices, sanitation services, and hy-giene improvements lag far behindneed. There is new evidence, however,that suggests that the role of theenvironment in maintaining endemicand epidemic cholera is more complexthan previously thought.

Cholera seasonalityCholera is endemic in Bangladesh andmaintains a regular seasonal patternwith two peaks - one in the hotseason, from March to April, and theother in the post-monsoon season,from September to January.2 Theetiologic agent V. choferae can beisolated from patients as well as fromthe aquatic environment during epi-demics, but disappears from surfacewaters after the epidemics are over.The reservoirs or sites of survival andmultiplication of these pathogenic vi-brios during inter-epidemic periodswere unknown. Recent laboratory andfield studies, however, have demon-strated that V. choferae 0 I can surviveinside the mucilaginous sheath of ablue-green algae, Anabaena \'ariahifis,for more than a year. These blue-greenalgae are now considered to be areservoir of V. choferae in the aquaticenvironment,3 and the cholera seasonin Bangladesh is related to the seasonalalgal bloom formation.4

During algal blooms in epidemicperiods, the algae die and disintegrate.The V. cholerae 01 which survived inthe mucilaginous sheath are released,and are in favourable conditions formultiplying in surface water. They getglucose, calcium, magnesium salts, etc.from the decomposition of the muci-laginous sheaths of the blue-green algae.During algal blooms, both the pH andthe salinity of the water increases, whichalso favours the growth of V. cholerae.Under all these favourable conditions,

its kind, began in southern India andspread around the coastal areas of theBay of Bengal to Bangladesh, andsubsequently to many other countries.While the 'new' cholera organismdiffers serologically from the previousepidemic-causing V. choferae 0 I or-ganisms, early evidence suggests thatthe new organism, called V. choferaeo I39-Bengal, is similar to Classicaland EI Tor cholera in terms of theclinical disease it causes, its transmis-sion pattem, and its epidemiology, butprevious exposure to both EI Tor andClassical cholera provided no immu-nity to 0 I39-Bengal, and there were ahigh number of cases as the firstepidemic wave swept through. The0139- Bengal epidemic entered south-

The spread and control of cholera inBangladeshby M.S. Islam and O.M. BatemanWhile researchers are learning more and moreabout the cholera bacterium, improvements insanitation and hygiene behaviour are still thebest defence.CHOLERA HAS A long history ofcausing life-threatening epidemics, andit continues to do so even now. In1991, when the seventh cholera pan-demic reached Latin America, therewere 391 220 reported cholera caseswith 4002 deaths. In the same year inBangladesh, there were an estimated210 000 to 235 000 cases and over8000 deaths in the months of Septem-ber, October, and November alone. I

Historically, cholera epidemics havebeen caused by Vihrio chofeme 0 I,either the 'Classical' or 'EI Tor'biotype. The seventh pandemic and themajority of the cases reported in 1991were caused by EI Tor.

More recently, an epidemic of non-01 V. chofeme, the first described of

Cholera continues to flourish. in part because of high population growth anddensity, poverty. and a lack of water and sanitation services.

20 WATERLINES VOL.12 NO.4 APRIL 1994

Q:;0-8uiiiz

I t=Cholera may also he transmitted through the consumption of contaminated fish, oyst('J's, crahs, or other shel(fish.

the rapid multiplication of V. cho/eraeo I takes place, and the water becomesheavily contaminated.

TransmissionPrimary transmission Cholera may betransmitted from the aquatic environ-ment to humans in a number of ways.During epidemic seasons, V. choleraemultiply in the aquatic environment.This may be triggered by the multipli-cation of blue-green algae and otherfavourable conditions in the aquaticenvironment, as described earlier.When people interact with the heavilycontaminated surface water ponds,lakes, canals, or rivers to bathe, wash,and, sometimes, to drink, it is then thatthey may contract the disease. Thismay be the primary mechanism bywhich the cholera organisms are trans-mitted from the aquatic environmentto humans. The transmission may alsooccur through the consumption ofcontaminated fish, oysters, crabs, orother shellfish.

Studies have shown that the inci-dence of cholera in fishing communi-ties in Bangladesh is higher than infarming communities. It is likely thatone individual contracts the diseaseduring a fishing expedition, whichoften lasts for several days, when thesurface water is used by the fishermenfor all purposes, including drinking.The fish that are caught are left in theboat without refrigeration, where theyoften deteriorate and become contami-

nated. The fishermen often sell thebest fish in the market and take theunsold, spoiled fish back home foreating. Even though this fish may thenbe well cooked, improper handling canlead to the contamination of kitchenutensils and other foodstuffs.

There are a number of reports fromseveral cholera epidemics about thedifferent kinds of fish which act as thevehicle for introducing \I. cho/erae 01from the aquatic environment to thehuman population.5

Secondary transmission Once the or-ganisms are brought to the communityand get a foothold via an index case(the first individual to catch the dis-ease), cholera then spreads to thesurrounding population by all thecommon modes of faecal-oral trans-mission. This continued spread isusually a result of inadequate water andsanitation services and poor personaland domestic hygiene practices. It hasbeen demonstrated, for example, thatwhen a family member develops chol-era, a quarter of that family's contactsmay develop cholera within days, andat least an additional quarter may haveasymptomatic cholera infections be-cause of poor hygiene practices.

Defecation andtransmissionOne of the main means of spreadingcholera from infected people to the

surrounding population in developingcountries is through indiscriminatedefecation. In Bangladesh, as in manycountries, people who have no accessto latrines usually defecate on thebanks of ponds, canals, or rivers, wherewater is readily available for washingafterwards. Those who can afford tobuild low-cost latrines often buildhanging latrines, also on the banks ofponds, canals, or ditches. The samewater bodies that arc contaminated hyopen defecation or hanging latrines arcalso used for personal, domestic, andhousehold purposes, including bath-ing, washing, swimming, cooking and,occasionally, drinking.

The photo on page 22 illustrates atypical scene in which hanging latrinesare located on the bank of a watersource, and where people are using thesame water source for a variety ofpurposes. It is easy to see how thesesorts of water and sanitation practiceshelp to maintain a cycle of \I. cho/eraein the population and the nearby watersources.

A number of studies have shownthat contaminated surface water isimportant in the transmission of V.cho/erae in the environment. It wasfound that once cholera was introducedinto a neighbourhood (by whatevermeans), its subsequent spread wasassociated with the use of pollutedsurface water sources shared by house-holds in the neighbourhood. It wasfound that the proportion of contami-nated water sources used by the index

WATERLINES VOL.12 NO.4 APRIL 1994 21

o-0~oJ:~

The same water source is usedfor washing c/othes, hathing,fishing, defecating, and as a source of drinking-water.

case and neighbouring households dur-ing the 12-day study period were 6Xper cent of tanks, 46 per cent of canalsand rivers, 44 per cent of ditches, and() per cent of tubewells. Overall. 57 percent of all surface water sourcescontained V cho/c/"(/e. The proportionof stored water in the households thatwas contaminated included I() per centof the stored drinking-water fromsurface sources, and 13 per cent of thestored cooking water from surfacesources. It was found that intra-neigh-bourhood and intra-family choleratransmission was primarily via con-taminated surface water.

EnvironmentalinterventionsCholera can be transmitted throughcontaminated water or food and fromperson to person, though the primaryroute is water-borne transmission. Inall cases. the primary barrier to thefaecal-oral transmission of cholera isto keep the cholera organism out of theenvironment in the first place. This canonly be achieved by disposing offaeces in a sanitary way so that thecholera-containing faeces do not con-taminate water bodies or the environ-ment. What may distinguish cholerafrom other diarrhoea-causing organ-isms is the additional risk of a personbecoming infected with V. cho/e/"(/£'from the natural aquatic reservoir, as

described earlier. Figure I shows howsusceptible people in a communitymay become infected, either throughexposure to the natural aquatic reser-voir or via faecal-oral transmission(similar to many other diarrhoea-causing organisms).

The existence of two possible routesof infection. with V. cllo/erae, theaquatic reservoir and faecal-oralroutes, and the ability of V. cllO/eraeto multiply rapidly in water, addadditional dimensions to cholera con-trol efforts in areas where communitieshave access to surface water bodies.For the interruption of faecal-oraltransmission, the primary barrier isadequate sanitation to keep contami-nated faeces out of the environment.When this primary barrier is absent orimperfect, personal and domestic hy-giene behaviour must be improved toavoid or destroy contaminating organ-isms and to prevent transmission inhouseholds and in the community.This behaviour includes water-sourceselection. water storage and handlingbehaviours, food hygiene, and hand-washing.1>

A study in Bangladesh found thatlower grade government employeesliving in government quarters providedwith sanitary latrines and a piped watersupply experienced cholera frequently,whereas the upper grade employees,also living in government quarters andprovided with sanitary latrines andpiped water supply, almost never

contracted cholera. Similarly, peopleliving in upper-class residential areasof Dhaka never contracted cholera inthe midst of even the most severeepidemics. The main differences be-tween the upper and the lower-incomegroups were in the personal anddomestic hygiene practices.7 Epidemiccholera cannot be prevented by theprovision of clean water and sanitationalone; appropriate hygiene behaviourchanges must accompany the provisionof hardware.

In the case of V. cllO/e/"(/e, adcquatesanitation and improved hygiene alonemay be expected to have less effecton transmission than in the case ofdiarrhoea-causing organisms that relyexclusively on faecal-oral transmis-sion. With an aquatic reservoir. sllscep-tible individuals may continue to be atrisk of infection. even if faecal-oraltransmission is completely interrupted.The obvious means of avoiding suchtransmission, that is drinking onlywater from a clean source such as adeep tubewell or chlorinated. pipedwater, is also a cornerstone of theprevention of faecal-oral transmission.While one may speculate about addi-tional measures to avoid the transmis-sion of cholera from aquatic reservoirs,the first step is to avoid using unsafesurface water for personal and domes-tic purposes. In summary, interruptingthe spread of cholera involves severallong-ternl interventions. Priority meas-

22 WATERLINES VOL. 12 NO.4 APRIL 1994

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Figure I. The aquatic elll'ironment and transmission of V. cholerae.

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V. cholerae again releasedinto water bodies

Water bodies used bycommunity members for multiple

purposes including drinking

infonnal consultation on improved water alllisanitation hygiene behaviours for the reductionof diarrhoeal diseases. Geneva. 18-20 May1992.

7. Khan. M.W. and Shahidullah. M .. 'Role of""ateI' and sanitation in the incidelll:e of cholerain refugee camps', Trallsacl;olls 1!f'lhe RoyalSoc;ely o/"I;'opil'<ll Med;cille lIlId lIyg;elle. 76.pp.373-7. 1<)82.

M.S. Islllm ;.1 lIlI A.I'.IOC;ale Sciellli.1'I ;11 IfteLlIfJo1'lllory Sci/'III'",1 /);1';.1';011. alld O.M.RlIlel1l11l1 ;.Il11l l:i';del1liologi,1'I ;11 IIII' Commllll;lyflellllh /);1';.1;011 of III" IlIIe/'lllll;1II1II1 Cellll'e .till·/);lIl'rhOelll /)isell.\'(' Re.\'('lIl't'h - IIc/llgllllle,l'II,GPO Box 128. /)IIlIkll 1111111,Ih/llglllllesh.

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Inadequate sanitarydisposal of faeces

Secondary spread of V.cholerae to other family and

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Susceptible person contractsthe disease, probably from theaquatic reservoir, and acts as

index case

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-~ROBENS

'Long-tenn persistence of toxigenic Vihriocholel'll 01 in the mucilaginous sheath of ablue-green algae. Allahaella \'lIriahilis· • .follr-lIal of Tmpil'<ll Medicil1e al1d Hygiel1e, 93.pp.133-9. 1990.

4. Cockbum, T.A. and Cassanos. J.G .. 'Epide-miology of endemic cholera', PI/Mil' Healll,Rel'orts. 75. pp.791-803. 1960.

5. Feacham. R.G" 'Environmental a.spects ofcholera epidemiology. I. A review of selectedrepons of endemic and epidcmic situationsduring 1961-80'. Tmpil'<ll D;seases Bl/l/el;lI.78. pp.675-98. 1981.

6. Bateman. O.Moo 'Diarrhoea transmission anddomestic hygiene behaviour: Pcrsonal anddomestic hygiene'. Presented at a WHO

ures to control cholera transmissioninclude:I) The use of water from clean sources

only, for all personal and domesticpurposes. This will involve ensuringconvenient access to abundant quan-tities of protected or piped water.

() Improved water handling and stor-age to prevent the contamination ofwater between the source and thepoint of consumption. This mayinvolve improved containers orsmall-scale technologies such asputting spigots on tanks, as well aschanges in behaviour.

I) Where abundant quantities of cleanwater cannot be assured in the shortterm, specific high-risk water-re-lated behaviour should be targetedto reduce the risk of cholera trans-mission in the interim, while long-term issues of adequate access arebeing addressed.

I) Improved sanitation to interrupt theepidemic spread of V. cho/erae.This includes access to a sanitarylatrine and its use by all of thecommunity members, all of thetime, to prevent the faecal contami-nation of the environment.

:) Adequate food hygiene, includingpreparation, storage, serving, andeating.

,) Adequate personal hygiene, particu-larly handwashing.Finally, it must be re-emphasized

that in most settings the prevention ofcholera cannot be achieved by techni-calor hardware interventions alone,but changes in behaviour must alsotake place. With this in mind, choleracontrol efforts should include strong,locally appropriate hygiene educationcomponents .•

AcknowledgementsThis work was supponed by the IntemationalCel1lre for Diarrhoeal Disease Research. Bangla-desh. The ICDDR.B is supponed by countries andagcneies which share its conccm for the hcalthproblems of developing countries. Current donorsinclude: the aid agencics of the govemments ofAustralia. Bangladcsh. Belgium. Canada. Dcn-mark. Japan. The Netherlands. Norway. SaudiArabia. Swcden. Switzerland, the United Kingdom.and the United States; intemational organizationsincluding Unicef. UNDP. the UN Population Fund.WHO: and private foundations. including the FordFoundation and the Sasakawa Foundation.

We thank Mr Manzurul Haque for secretarialassistance.

ReferencesI. Siddique. A.K., Zaman. K.. Baqui. A.H ..

Akram. K .. Mutsuddy. P .. Susof. A., Haider.K., Islam. S .. and Sack R.B. 'Cholera epidem-ics in Bangladesh: 1985-91 '. }oll/'l1al ofDiarrhoeal Disease Research. 10. pp.79-86,1992.

2. Islam, M.S .. Drasar. B.S .• and Sack. R.B .. Theaquatic environmental as a reservoir of VihrioCholera: A review', }oll/'l1al of DiarrhoealDisease Res('arch. II, pp.197-206, 1993.

3. Islam, M.S., Drasar. B.S., and Bradley. D.1 .•

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