Math in the Time of Cholera

The renowned microbiologist Dr. Rita Colwell delivered a scintillating public lecture at BIRS’ September 2010 gala event, giving listeners a surprisingly digestible overview of her voluminous and complex research projects over the past four decades, and illustrating how mathematics, microbiology and sociology have managed to unite to save lives in the fight against cholera.

In introducing Dr. Colwell, Tom Brzustowski valiantly attempted to summarise her rather astounding curriculum vitae in a simple illustration: If he were to make a New Year’s resolution for 2011, to study two of Dr. Colwell’s research publications every day, then by New Year’s Day in 2012 he would have a month’s supply still to go. He carried on in a similar vein when it came to Dr. Colwell’s rather comparably impressive collection of 55 honorary degrees.

Dr. Brzustowski particularly stressed the point in his introduction that not only has Dr. Colwell achieved excellence in the sciences throughout her remarkable career, but that she has gone a step above: she has achieved influence. As Director of the US National Science Foundation from 1998-2004, she was, in Mr. Brzustowski’s estimation, one of the most influential scientists in the world. Many worthy initiatives currently underway are the fruits of her early labours at the Foundation. Brzustowski labeled the major theme throughout her career as being “elegant science that saves lives”. Her lecture at the Banff Centre was a perfect introduction to her elegant yet powerful research.

Climate, Oceans, and Infectious Disease: The Cholera Paradigm

As early as the fourth century BC, Hippocrates alerted students that “whoever wishes to pursue the science of medicine must first investigate the seasons of the year and what occurs in them”. Since her graduate school days, Dr. Colwell has been doing just that with relation to epidemics of cholera, although she has added to the study of seasons such other factors as chlorophyll measurements and ion concentrations in water.

Cholera has long been a menace to public health, but its destructiveness has increased in recent centuries as population density, and the continued reliance on single sources of water, has increased. The link between water contamination and cholera outbreaks was first pinpointed by the English doctor Sir John Snow in 1849, Dr. Colwell explains, when he plotted the instances of cholera during an epidemic in London, and found a strong concentration of people affected by the illness around the Broad Street pump. The introduction of chlorination into the running water supply in wealthier states has largely eradicated the disease in the more economically developed world; however, cholera remains a persistent problem in many countries, notably in southern Asia and in Africa.

Dr. Colwell has thus dedicated a large part of her career to better understanding the bacterium which causes it, as well as what forms of appropriate technology can be used by individuals in less developed states to protect themselves and their families from the severe diarrhoea and dehydration that it causes.

She highlighted for us several important findings that she has made:

  • The cholera bacterium can become dormant. This makes it particularly difficult to detect without the use of a special staining agent, and also means that it never fully disappears from many water supplies.
  • Like influenza, cholera is extremely genetically diverse. Different strains emerge in different environments; hence, there is little viable hope for a universally-effective vaccine. Still, genetic research can help to track fierce pathogenicity in certain strains which would cause worse epidemics, and appropriate precautions can be taken.
  • Crucially, Dr. Colwell and her colleagues have found that cholera is very frequently associated with plankton. A single plankton can carry up to 100 000 bacteria. She has found this to have very promising implications for the methods that can be used to protect people from illness.

Throughout her career, Dr. Colwell has mixed the academic with the pragmatic. Her work has been both international and interdisciplinary throughout. She has worked with biologists, meteorologists and statisticians in charting sea surface temperatures (SST) in the Bay of Bengal, relying upon satellite data to help predict likely times and locations of cholera outbreaks. Likewise she has been involved in developing more complex predictive models based on environmental parameters such as temperature, chlorophyll measurements, ion concentrations, and salinity. Not least she says that over the years she has forged a “love affair with mathematicians” who have managed to carry on modeling when the data is scarce, significantly furthering hypotheses and research.

Based on all of this research, Dr. Colwell has played an active role in helping to prevent outbreaks in local Bangladeshi communities. While in places like Latin America, instances of cholera illnesses can be prevented by simply instructing people to boil their water, in Bangladesh fuel is scarce, and such an approach would be impossible. Recalling her findings relating to the linking of cholera with plankton, Dr. Colwell instructed women in Bangladesh to fold their sari cloth in four and to filter the water they drew through the cloth before use. Plankton is too large an organism to slip through four layers of mesh. Subsequent investigations showed that this practice reduced the instances of cholera in the towns where women were employing it by at least 50%, and it transpired that many of those who did fall ill did so after having been to visit friends or relatives in neighbouring communities where the practice had not been introduced. For this work, Dr. Colwell was recently awarded the Stockholm Water Prize by the Stockholm International Water Institute and His Majesty King Carl XVI Gustaf of Sweden.

In this presentation which she described as “kaleidoscopic”, with the corresponding slides nearing “subliminal”, Dr. Colwell demonstrated how mathematical modeling can lead to a better understanding of epidemiological processes and can focus responses. Pairing up with other academic disciplines, it can save lives. Such a high-profile scientist, Dr. Colwell and her lecture will be a reminder to BIRS participants and to the world of just the kind of impact that good research can have.