Reduction of cholera in Bangladeshi villages bysimple filtrationRita R. Colwell*†‡, Anwar Huq*†, M. Sirajul Islam§, K. M. A. Aziz§, M. Yunus§, N. Huda Khan§, A. Mahmud§,R. Bradley Sack¶, G. B. Nair§, J. Chakraborty§, David A. Sack§, and E. Russek-Cohen储*Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, MD 21202;†Department of Cell Biology and MolecularGenetics, University of Maryland, College Park, MD 20742;§International Centre for Diarrhoeal Disease Research, Dhaka, Bangladesh;¶Departmentof International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205; and储Biometrics Program, Department ofAnimal and Avian Sciences, University of Maryland, College Park, MD 20742Contributed by Rita R. Colwell, December 5, 2002Based on results of ecological studies demonstrating that Vibriocholerae, the etiological agent of epidemic cholera, is commensalto zooplankton, notably copepods, a simple filtration procedurewas developed whereby zooplankton, most phytoplankton, andparticulates >20␮m were removed from water before use. Effec-tive deployment of this filtration procedure, from September 1999through July 2002 in 65 villages of rural Bangladesh, of which thetotal population for the entire study comprised ⬇133,000 individ-uals, yielded a 48% reduction in cholera (P < 0.005) compared withthe control.Cholera is a disease that continues to ravage developingcountries and reemerges sporadically elsewhere throughoutthe world. According to the World Health Organization (WHO),58 countries have officially reported cholera in 2001, with a totalof 184,311 cases and 2,728 deaths (1). However, there were293,113 cases of cholera worldwide in 1998, with 10,586 deaths.These annual figures of WHO actually represent the tip of theiceberg, because the morbidity and mortality caused by Vibriocholerae is grossly underreported owing to surveillance difficul-ties and also for fear of economic and social consequences (2).In fact, several cholera endemic countries, e.g., Bangladesh, arenot included in the WHO report. In 1991, after almost 100 yearswithout cholera, outbreaks in 16 Latin American countriesresulted in ⬇400,000 reported cases of cholera and ⬎4,000reported deaths (3).That cholera is a waterborne disease has long been known(4–6). Furthermore, surface water has been linked with trans-mission of cholera since the pioneering work of Snow in 1854 (7).Demonstration of the potential for water to transmit cholera wasprovided by Koch, who, after Pacini first described the Vibrio (8),isolated and characterized the bacterium, which he named Vibriocomma, and was able to find it in pond water used by an Indiancommunity suffering a cholera epidemic (9).The association of pathogenic vibrios with zooplankton wasreported in 1973 by Kaneko and Colwell (10) and of V. choleraewith copepods by Huq et al. in 1983 (11). Commensal occurrenceof Vibrio spp. in the copepod gut was demonstrated by Sochardet al. in 1979 (12). A few years later, preferential attachment ofV. cholerae to copepod surfaces, egg cases, and the copepod oralregion was reported by Huq et al. (11). Extensive data have sincebeen accumulated showing that planktonic copepods play amajor role in the multiplication, survival, and transmission ofcholera (13–17). That environmental V. cholerae O1 can causecholera has been established by molecular genetic evidence (18).During spring and late summer in Bangladesh, phytoplanktonblooms occur, followed by zooplankton, with heaviest bloomsoccurring in September and October (13, 19). Each year, theseasonal zooplankton blooms, in turn, are followed by choleraoutbreaks (11, 13). It has been determined that a single copepod,depending on species and size, can carry up to 104cells of V.cholerae (11, 17). Thus, a copepod bloom can result in thenumber of V. cholerae per ml of water comprising an infectivedose, based on findings from human volunteer studies, showingthat ⬇104to 106V. cholerae O1 can produce clinical cholera (20).Patchiness in copepod distribution, often species specific in theaquatic environment (21), can result in significant variability inthe number of copepods in water taken directly from a pond orriver for drinking.Village populations of Bangladesh depend on untreated sur-face water for household use, especially during times of flooding(22). Surface water from ponds and rivers is used by somevillagers as a source of drinking water for reasons of taste,convenience, or a local belief that ‘‘quality’’ water is ‘‘natural,’’i.e., not chemically treated (15, 22). Furthermore, with thecurrent arsenic crisis in Bangladesh, as many as half of the wellsdrilled in the late 1960s as the answer to Bangladesh’s severesurface water pollution problem have been found to be contam-inated with arsenic in amounts that exceed 50 ppb, with someconcentrations even 10 times higher in contaminated areas(23–26). According to a recent study conducted in Araihazar inBangladesh by WHO, ⬎30 million people are exposed to unsafelevels of arsenic in their drinking water, and 20% of the arseniccontaminated tube-well water users switched back to untreatedsurface water (27). In addition, studies showed that tube wellwater contained 104to 106total bacteria by acridine orangedirect count (28) and a high incidence of zooplankton, as well ascoliforms and other bacteria (29). These findings indicate thatsurface water has again become important as a source ofhousehold water and for drinking when no other safe water isavailable.Although boiling water before drinking is effectively the betterpractice, because it will kill all waterborne pathogenic microor-ganisms, it is not used routinely in the villages because fuel woodin rural Bangladesh is both in very short supply and costly.Moreover, during severe flooding, which frequently occurs inBangladesh, there are geographical areas that experience reduc-tion in the quality of life to mere survival, when even the barestnecessities are difficult to obtain and building fires to boil wateris simply not possible.It is common practice in villages in Bangladesh to use cloth,frequently a flat, unfolded piece of an old sari, to filter home-prepared drinks. In laboratory experiments employing electronmicroscopy, we found that inexpensive sari cloth, folded four toeight times, provides a filter of ⬇20-␮m mesh size, small enoughto remove all zooplankton, most phytoplankton, and all