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Dr. Colwell's Remarks


"A Global Thirst for Safe Water: The Case of Cholera"

Dr. Rita R. Colwell
National Science Foundation
2002 Abel Wolman Distinguished Lecture
National Academy of Sciences
Washington, DC

January 25, 2002

See also slide presentation.

If you're interested in reproducing any of the slides, please contact
The Office of Legislative and Public Affairs: (703) 292-8070.

Good afternoon to everyone, and thank you, Dr. Luthy, for a gracious introduction. I'd like to thank everyone from the Water Science and Technology Board who helped organize this year's Abel Wolman Distinguished Lecture. A very special thank-you to Stephen Parker and Anita Hall for their dedicated work in bringing us all together for this event.

It is an honor and a pleasure to be here today at the Academy, especially since our topic--"the global thirst for safe water"-- presents a compelling challenge.

Today we commemorate Abel Wolman, and as part of that I would also like to recognize the work of his son, "Reds" Wolman, another water luminary in his own right and a friend whom I've known for many years. Reds is a fellow member of the National Academy of Sciences and one of my predecessors at this podium in giving this lecture named for his father.

I note that the first person to give this lecture was Luna Leopold, sometimes called the godfather of hydrology. However, I want reach back for a moment to his father--Aldo Leopold.

Aldo Leopold, a great environmentalist and an eloquent writer, borrowed a metaphor from one of the tall tales about the mythical lumberjack, Paul Bunyan. This was the "Round River" of early Wisconsin, the river that flowed around, ceaselessly, into itself.

Aldo Leopold extended the meaning of the Round River to the "never-ending circuit" of energy through life and the environment.

That imaginative notion is evocative today, because it neatly conveys the central thesis of how we need to view water on a planetary scale.

The cycling of water and our global interconnections mean that all of us are "living downstream"--everyone on this planet. Thus, we need to step back and take a clear, dispassionate look at the world's supply of water, using all available tools, from the nanoscale to the global scale.

Just as Abel Wolman brought new insight to developing a dependable method for treating drinking water, so in the 21st century we have to develop an integrated approach across the disciplines to understand the complexity of water issues worldwide.

I'm going to move from the broad picture to focus on one specific aspect of that complex challenge: my own life's work on water and infectious disease, highlighting the case of cholera.

I'll conclude with a survey of how we can use new ways of thinking, such as complexity, as well as new tools--from genomics to mathematics to NSF's proposed nationwide ecological observing network--to deal with the new realities of our "downstream" world community.

[graphic of where fresh water is]

I use this illustration--not because it is news to most of you--but to draw the "bigger picture." Water is indeed everywhere, but there are very few drops left for us to drink. Earth is the blue planet, but only 2.5% of our water is fresh. Of that mere 2.5%, glaciers and ice caps comprise two-thirds. Of the remaining third of this freshwater (again, a third of that 2.5% that is fresh water), 20% lies in remote, inaccessible locations.

We are left with 80%--and of that one-third of 2.5%, three-quarters is not usable, because it comes in the form of monsoons and floods. To sum up, according to the World Water Council, human beings have access to less than eight-tenths of one percent of the total water on this blue planet.

Where there is scarcity, there is contention. Bodies of water can unite and divide the nations that depend on them.

For example, approximately 260 rivers around the world flow through two or more nations, leading to dual national claims for the water. But some of these rivers no longer complete their flow to the sea.

The Yellow River did not reach the sea for more than an aggregate of seven months in 1997. Closer to home, the "mightiest river" of the American southwest, the Colorado, now terminates in a "bone-dry" delta in Mexico.

A Mexican biologist, quoted in the Washington Post this month, said flatly, "The Colorado ceases to exist here"--in Mexico. Water management has become, more than ever before, a fundamental element in national security, for every nation.

Arguably, although only one war in history was fought directly over water--this was 4500 years ago on the Tigris River--the thirst for water on our planet has never been greater, and it is growing. We can predict wars over water in the not so distant future.

[Graph: world population growth rate; three scenarios]

In the words of a recent World Water Council study, "the arithmetic of water in coming decades does not add up," in view of the expected growth in the world's population.

Global population reached 6.1 billion in mid-2000. This graph shows the estimated and projected populations of the world from 1950 to 2050, according to three different scenarios: low, medium, and high.

By 2050, world population should reach between 7.9 billion--the low scenario, and 10.9. billion--the high scenario.

[World map: population growth rates]

Where are the people now and where will they be? Populations of more developed regions, shown in lighter colors, grey and white, are expected to change little over the next half-century.

The aggregate population of the less developed regions, however--shown in red and yellow, is expected to rise from 4.9 billion in 2000 to 8.2 billion in 2050. Moreover, the fastest growth will be in the least developed nations.

[World map: where the water is]

This map looks at the world through a water lens. Blues and greens show regions with sufficient ground and surface water to sustain their populations, while red and yellow denote regions without adequate water. Most of Africa and southwest Asia have serious water deficits. Comparing the previous map--population growth--to water supplies, we see that the water equation is out of balance, and getting dramatically worse.

Already in the year 2000, 1.1 billion people lacked safe water. More than twice as many--2.4 billion--lacked adequate sanitation.

Water use is expected to increase by 40% over the next two decades. Of the new demand, 17% will be needed to grow food.

For example, it requires 1000 tons of water to produce one ton of wheat, and 2000 tons of water to produce one ton of rice. Agriculture is using more water, and industry's use of water is also increasing--at a much faster rate, in fact, than that of agriculture.

[Wastewater treated by effective treatment plants]

This graph slices the facts another way but the conclusion is the same. We see a dramatic gap between the treatment of wastewater in developing nations, compared to North America and Europe.

From these data flows a stark underlying truth--this discrepancy is related to global security. We recently lost Sir Peter Blake, world sailor and environmentalist, but his wisdom about water lingers.

As he put it, "There are more refugees escaping poor water quality today than fleeing war." His observation highlights a key issue: as serious as the gap in water quantity is, it is only one factor in the equation. Equally critical is water quality.

[Access to safe drinking water VS under age 5 mortality rate: countries compared]

We know that water quality and public health are intimately linked. This graph shows how that differs between developing and developed nations. On the left, in blue, we see the nations with best access to safe water. On the right, in yellow, we see the comparatively high mortality rates in developing nations without access to safe water.

Water security scholar Aaron T. Wolf writes, "While water quantity has been the major issue of the 20th century, water quality has been neglected to the point of catastrophe." That is particularly true in the case of waterborne infectious diseases.

[Historic collage: Chicago, circa 1900]

While we face vast and complex challenges on this front today, the history of drinking water quality in the United States holds some valuable lessons. It was only a century ago that many Americans first began having access to safe drinking water. At the end of the 19th century, one out of ten U.S. infants died of water-borne typhoid or dysentery before they turned one year of age.

Typhoid epidemics were common. In Chicago, for example, citizens died by the thousands -- victims of Lake Michigan water polluted with raw sewage.

[Schuylkill River filtration plant, Fairmount Waterworks, Philadelphia]

After the Civil War, filtration was introduced to remove offensive particles and to improve the aesthetic quality of the water. Here we see Fairmount Waterworks on the Schuylkill River in Philadelphia. At first, however, filtration was not given credit for reducing disease.

[Graph of U.S. typhoid cases, 1890-1940]

That changed after a typhoid epidemic hit the Hudson River Valley in the 1890s. It soon became clear that communities that filtered water had fewer typhoid cases than those that did not. When filtration was introduced, the number of cases plummeted.

In 1908, Chicago and the Jersey Water Works became the first utilities in the country to use chlorine for disinfection.

[Abel Wolman collage]

The precipitous decline of typhoid cases, coupled with the rise in water treatment plants, dramatically illustrates the impact of Abel Wolman.

By the 1920s and 30s, filtration and chlorination had virtually eliminated epidemics of major waterborne diseases from the American landscape.

Part of Wolman's genius was his ability to synthesize research from disparate fields to fashion a holistic solution. My own journey in science has brought me to the realization that an integrative approach is critical to scientific progress.

My research, which has helped to link cholera outbreaks to climate, has rested on findings from several disciplines--fields that at first might not appear to be at all related.

My voyage of discovery, the study of how factors combine to cause cholera, began more than 30 years ago. Our team gradually accumulated the evidence that a disease like cholera does not exist in a vacuum.

In endemic regions, cholera appears seasonally. Early studies, summarized by Pollitzer in his compendium, noted that cholera outbreaks showed several seasonal peaks, although definitive data were not yet obtained.

As we now know, environmental, seasonal and climate factors influence the populations of the larger host organism for cholera, the copepod, which we saw in the video. It peaks in abundance in spring and fall.

Add in economic and social factors of poverty, poor sanitation, and unsafe drinking water, and we begin to see how this microorganism sets off the vast societal traumas of cholera pandemics.

We explore the problem on different scales. We study the relationship among bacteria, its copepod host, and many other ecological and social factors. On a microscopic level, we look at molecular factors related to the toxin genes in vibrios.

My team now comprises collaborators working in the coastal areas of Southeast Asia; others in Central and South America, where cholera reemerged in the last decade; and researchers from the National Aeronautics and Space Administration (NASA).

All are needed to elucidate ancient questions--such as from where does cholera arise, how does it spread in a given community, and what can be done to prevent it--especially in developing countries without central water treatment?

[Cholera statistics, 2000: WHO]

It is an enormous challenge. The latest numbers of cholera cases from the World Health Organization are for the year 2000: 137,071 cases and almost 5,000 deaths.

But note that those figures don't include Bangladesh, Pakistan, both North and South Korea, and several other countries, whose aggregate numbers may equal those reported for the rest of the world, shown in this slide.

[Table: worldwide cholera, 1991]

To give an idea of possible worldwide totals, especially in years of epidemics, a representative year is 1991, when over 200,000 cases were counted in three months in Bangladesh alone.

During the epidemic from August through October, a thousand cholera victims entered the cholera hospital in Dhaka, Bangladesh every day during the peak month of that year.

[Map: Global spread of cholera, 1961-91]

The map summarizes the epidemic years of the seventh pandemic, which began in the Celebes in 1961. There is now consideration that we may be in an eighth pandemic, since a new serotype of V. cholerae--0139--has emerged as an epidemic form.

[Map of cholera spread from old medical textbook]

This map, tracing the path of cholera's spread, is taken from an 1875 medical textbook. One sees little change today in the areas where cholera is endemic. But cholera is much older than that. A disease similar to cholera was first recorded in Sanskrit writings in what is now India about 2,500 years ago. But almost everything we know about it is very recent.

[John Snow map: cholera cases in London, 1854]

By the mid-1800s, British physician John Snow plotted deaths from cholera in a London neighborhood related to water pump locations. This was the first epidemiological study ever done.

[Old cartoon: pump and death]

According to the mythology, Snow removed the handle of the water pump in the affected area of London, and the epidemic abated.

Italian scientist Filippo Pacini--then a young medical student--was the first to describe the cholera bacterium in 1854. However, he was ignored because at that time the germ theory of disease was not accepted.

German physician Robert Koch redefined the bacterium as the causative agent of cholera and isolated what he called "Vibrio comma" --because of its curved shape--in pure culture in 1883.

[intestinal chemistry diagram]

But it wasn't until 1959, more than 140 years after the beginning of the first pandemic, that an Indian scientist, Sambhunath De, discovered the Vibrio toxin.

The production of this toxin by the bacterium changes the permeability of the cell membrane, enabling secretion of massive amounts of water and electrolytes into the lumen of the intestine.

[Chesapeake Bay cholera sampling sites]

In the 1970s, my colleagues and I realized that the ocean itself is a reservoir for V. cholerae, including V. cholerae 01, when we identified the organism in water samples from the Chesapeake Bay.

Earlier detection methods for V. cholerae 01 were developed strictly for testing clinical samples. In environmental samples, V. cholerae 01 is more difficult to detect.

The organisms may be more dispersed in the water and they may be dormant--not actively metabolizing.

[copepod close-up]

Here we see a copepod close up--the minute relative of shrimp which forms part of the zooplankton populations. This microscopic animal lives in salt or brackish waters and travels with currents and tides.

Copepods harbor both dormant, nutrient-deprived, and culturable vibrio. The bacteria can survive as an inactive, spore-like form in the guts and on the surfaces of the copepods between the epidemics.

This copepod is a female whose egg case is covered with vibrios. The vibrio can be cultured somewhat more easily in the summer months.

[graph: V. cholerae numbers on copepods]

In fact, a single copepod can harbor as many as 10,000 Vibrio cholerae cells. Most recently, we have used genetic techniques--PCR and gene probes--to detect Vibrio directly from environmental samples, confirming earlier immunofluorescent detection results employing monoclonal antibodies.

[Monitoring temporal patterns of cholera]

Moving to the larger picture, our most recent studies have used remote sensing imagery to gather data on sea surface temperature and sea surface height, discovering in the process a clear correlation between sea surface temperature and the periodicity of cholera outbreaks in Bangladesh and in South America.

Heating of surface waters, especially off a tropical or subtropical coast, results in an increase in phytoplankton. Through remote sensing, we can now determine when the phytoplankton bloom is occurring. The phytoplankton, in turn, provide food for zooplankton, such as copepods, which then increase.

[cholera outbreaks, SST and SSH]

We know that cholera epidemics are seasonal. Using remote sensing imagery, we recently discovered that, in areas of Bangladesh, cholera outbreaks occur shortly after sea surface temperature and sea surface height are at their zenith. This usually occurs twice a year, in spring and fall.

You see here the annual ebb and flow of cholera cases from October 1992 to November 1995.

[SST in Bay of Bengal]

Here, we see the waters warm in spring, are denoted by green and yellow, even red colors--a higher temperature, and then the monsoon cooling. The ocean warms once again in the fall, with some red visible at the mouth of the Ganges River. This cycle repeats year after year in the Bay of Bengal.

[Cholera in Latin America]

Let's move to the Western Hemisphere. The sea surface temperature there is influenced by the El Nino-Southern Oscillation, or "ENSO" for short. El Nino is the anomalous warming of the ocean surface that occurs periodically off the west coast of South America.

After a century without a major outbreak of cholera, a massive Vibrio cholerae epidemic occurred in the Western Hemisphere in the El Nino year of 1991, starting in Peru and spreading across South America.

We'll now see two videos side-by-side, showing sea temperature off South America in two contrasting years: one with an El Nino and one without. The videos, please.

[SST off South America in contrasting years]

On the right we see sea surface temperature fluctuating over an El Nino year, 1997-98. On the left, we see a year without El Nino, 1995-96. The comparison clearly illustrates the signature of El Nino.

Look especially at the coastal waters off Peru and Mexico, near the equator, and see how that area differs between the two years, notably in July through December.

[image: ship ballast release]

Incidentally, there is yet another dimension to the spread of cholera. We recently published a brief communication in the journal Nature on how ships can transport pathogens in their ballast tanks.

It turns out that such ballast harbors significantly large numbers of copepods--nearly the entire plankton population of ballast water can be copepods. They are hardy creatures--they don't need sunlight and they survive well in the hold of a ship during a long transoceanic voyage.

Some cholera outbreaks associated with shellfish may have originated with discharged ballast water. But these cases are episodic and not responsible for the endemic, annual cholera epidemics of Bangladesh or the massive epidemic of Latin America.

[sari cloth water filtering]

Although the explanation of cholera outbreaks is global in scale and includes many factors, the solutions can be surprisingly simple--and these can be implemented on a very local scale.

Cholera transmission is easily controlled by providing people with clean, uncontaminated water for drinking and bathing. As we saw in the film excerpt from Bangladesh, even at the most basic level, we have found that filtering water through several layers of sari cloth may be enough to prevent ingestion of infectious levels of V. cholerae by removing the particulate matter, including the zooplankton (copepods).

[cholera cases: sari vs. non-sari]

A sari cloth, readily available even in the poorest household, can be folded eight to ten times. This creates a 20-micron mesh filter, as we determined by electron microscopy. Here we see the results of testing sari cloth as a filter to remove plankton, which are much larger than 20 microns. Its use reduces the number of cholera cases by half or more.

As was shown 150 years ago, filtration is effective but now we know why, at least in the case of cholera: It removes the bacteria associated with plankton and it can be applied on a household-by-household scale.

As my group's research with Vibrio cholerae has shown, what appears to be a simple tightly circumscribed biological problem-a bacterium that infects people--can have ramifications and interrelationships on a global scale.

Our work has touched upon remote sensing, biodiversity, and even genomics, since we were partners in the sequencing of the Vibrio cholerae genome.

Our most recent results underscore the absolute importance of including social scientists in a project.

In our study villages, for instance, children may drink from a tube well but bathe in a canal or pond where clothes from cholera-infected individuals are washed and where sewage is directly discharged. Or villagers using sari filters nonetheless contract cholera on visits to infected households that don't filter water.

[Small chromosome]

Moving back into the laboratory, genomics has given us a powerful new tool to learn even more about cholera, at the molecular scale. In the year 2000, the genomes of the two chromosomes possessed by V. cholerae were sequenced.

The discovery of two chromosomes was interesting, because all bacteria were presumed to have a single chromosome.

[Large chromosome]

The toxin genes reside on the large chromosome. The sequencing data indeed confirm that V. cholerae is a versatile organism, able to live in several habitats, as well as to infect the human gastrointestinal tract.

[list of worst water-borne infectious diseases]

Each of the worst water-borne diseases presumably has its own complex ecology, and each needs to be studied in its own ecological context.

Complexity science, not available to Wolman and his compatriots, gives us a wonderful tool to help us trace the interconnections of epidemiology and ecology.

[World map: infectious diseases]

We need this approach at a time when strange diseases are emerging or reemerging from unexpected quarters. This map gives a global snapshot of infectious disease outbreaks in 2001 alone. We are learning of new mechanisms of survival and transmission.

Dr. Gerba at the University of Arizona, for instance, has found that enteric, or intestinal, viruses survive for very long periods of time in the depths of the sea. We have demonstrated the same for enteric bacteria in studies carried out in the Atlantic Ocean.


The outbreak of Cryptosporidium in Milwaukee, Wisconsin in 1993 --we see the organism here--illustrated the fact that even citizens of developed countries are "downstream dwellers."

Cryptosporidium is all too familiar in developing countries. In northeastern Brazil, 90% of the children are infected.

[Helicobacter pylori]

Another story--the strange case of Helicobacter pylori: In 1984, researcher Barry Marshall suspected a bacterial link to ulcers, and identified the culprit: Helicobacter pylori, and showed a link to blood type O.

In work done with my colleague, Dr. Shahamat at the University of Maryland, we have shown that Helicobacter pylori will persist in a dormant form in fresh water for up to a year or more. Subsequent research in Peru showed water transmission of H. pylori.

[Bangladesh tube wells illustration]

Complexity science, with its ability to integrate events taking place across the scales of space and time, gives us hope that we can trace the many facets of emerging and reemerging diseases.

Many of you may be aware of another story of water and Bangladesh. This is not directly a story of my own research, but it is one that cries out for the perspective of complexity.

Bangladesh is currently "grappling with the largest mass poisoning in history," according to the World Health Organization.

Estimates range from 20 million to 77 million people subject to chronic poisoning by arsenic in their drinking water.

How could this have come about? In pursuit of safe drinking water, more than four million tubewells, deep wells, have been installed in Bangladesh over the past two decades.

The object was worthy--to supply microbiologically uncontaminated groundwater, but the result has been unwitting poisoning. Not only that; in our own work we have shown that in times of floods, the tubewells can become contaminated with cholera bacteria.

Now, new sources of drinking water must be found in Bangladesh. The population is turning back to surface water, which makes our results even more timely. Here is a clear case of a water problem in which it was critical to map all the variables and their interconnections.

[new composite biocomplexity image]

Our challenge today is to apply all our tools of vision, from genomics to computers to satellites, to embrace and understand complex systems.

I use this array of images, from the small scale to the immense, to convey the connections within this complexity, as a perspective on water today. I call this approach "biocomplexity." For several years, the U.S. National Science Foundation has supported biocomplexity studies, in which interdisciplinary teams examine a wide array of interactions.


Recently NSF proposed a network called "NEON," shown here very schematically, without pinpointing specific sites. This is the planned National Ecological Observatory Network--an array of sites across the country furnished with cutting-edge sensor technologies.

[Instrumenting the environment]

Here's an imaginative concept of a NEON site fully instrumented (with apologies to the artist Rousseau). Networks such as NEON require state-of-the-art sensors of every stripe. Such a site will measure dozens of variables in organisms and their physical surroundings. I think of this as a biological "early warning system."

All the sites would be linked by high-capacity computer lines, and the entire system would track environmental change from the microbiological to the global scales. We can imagine how a network such as NEON could also serve to monitor disruptions by an attack of bioterrorism.

[women and children at water source in Bangladesh]

Our progress in understanding environmental interactions is closely linked to new insights in the social sciences. The puzzle of cholera outbreaks in Bangladesh contains many variables that only a social scientist can elucidate.

Only by incorporating the social sciences can we ground our theories in reality, and move our solutions into implementation.

I recall our studies in Bangladesh once again--how we were solemnly told that men would never accept drinking water that had been filtered through the garment of a woman. This turned out not to be a problem--as it happened, men had already been using sari cloth routinely to strain flies from their beer.

[collage of U.S. water facilities: Hoover Dam under guard, a water treatment plant.]

Back here in the United States, September 11 has transformed our nation's complacent view of water security. Now we are paying attention once more to our neglected public health programs, and to the security of our water treatment plants and dams.

Ultimately, water security is possible only if it embraces everyone living downstream. Like the "round river" I evoked earlier, the dimensions of water security overflow our borders to include the entire planet.

[Beverly lighthouse]

It has been said that we all live "by the grace of water." I grew up, in fact, by the water, just a block from this lighthouse in Beverly Cove, Massachusetts. The lure of the sea led me to my life's work in microbiology, which I have discussed today. This attachment to the sea also led to many hours serving as crew in sailing regattas with my husband.

I recall one of those sailing yarns now. It is said that one stormy night, the captain of a warship peered through the gloom--and he spotted a light, barely visible in the fog.

With a loudspeaker on the ship, the captain bellowed, "Unknown vessel, change your course to starboard!"

A voice across the water replied, "You must tack to starboard!"

Angrily the captain shouted back, "This is the ship's captain you are speaking to. You are in our path. Tack to starboard immediately!"

Again, a voice in the mist: "This is seaman first class Jones. Change course to starboard immediately!"

The captain bellowed his ultimatum: "This is a warship of the U.S. Navy. Tack to starboard or be destroyed!"

The voice replied, "Sir, this is a lighthouse!"

Sometimes a course change is vital. In regard to global water, I would suggest that now is one such juncture.

A lighthouse is a symbol of vigilance on our shores, so let's start at home. Today we can spend hundreds of thousands of dollars testing our water for heavy metals, but we monitor microorganisms only in the most elementary way. We now have the molecular tools--PCR, gene probes, microchips--to do highly sophisticated and accurate detection of pathogens in water.

We need to move beyond the fecal coliform test to full understanding of the microbial populations and the microbial ecology of our drinking water.

Nanotechnology, along with other initiatives by the National Science Foundation, offer the promise of great progress in this area. The bioterrorism threat lends even greater urgency to protecting our drinking water nationwide using the best science and best technology available.

It's time for us to move water science into the twenty-first century.

I would like to thank my staff, postdoctoral fellows, and students in the audience here today. I acknowledge with thanks their excellent hard work. And I'd like to recognize Lynn Simarski and Curt Suplee from the National Science Foundation, and Kirk, Josh, Deena, and others from NSF who worked diligently to perfect the graphics for this talk.



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