This week microbiologist Rita Colwell received the Stockholm Water Prize, which includes $150,000 USD. Dr. Colwell was recognized for her “numerous seminal contributions towards solving the world’s water and water-related public health problems.”
I interviewed Dr. Colwell at the 2008 meeting of the American Association for the Advancement of Science. Below are excerpts from that interview, on the role of the environment and climate in cholera outbreaks.
Q: What’s the most important thing you want people today to know about the environment and infectious diseases?
Rita Colwell: Infectious diseases are closely related to the environment. In other words, it’s important for us to understand seasonality, climate, and the drivers for infectious disease, and the fact that the ecology of the environment plays a very significant role in infectious disease outbreaks and their persistent patterns.
Q: Tell us more about this connection between infectious disease and the environment.
Rita Colwell: Let me give you an example. Cholera is a devastating disease in the developing world. It was a massive epidemic disease in the United States, but that was pre-1900, before water treatment and good sanitation was introduced to the country. The organism is resident on plankton, marine zooplankton — the small, microscopic animals of the sea. The organism is a marine bacterium, but yet it can also live in fresh water associated with plankton. It shows a definite seasonality, and so the cholera epidemics in Bangladesh are intense in the spring, and then even more intense in the fall, related to the plankton blooms. So we have been able to track these interactions using satellite imagery, using chlorophyll as a marker. Chlorophyll can be observed by the sensors of satellites, and they denote phytoplankton, small, microscopic plants of the ocean, on which the zooplankton feed, or graze. So we then can have a marker that allows us a prediction of when the zooplankton will be dominant, and shortly after that, the vibrios that cause the disease, the bacteria that cause the disease, then will become abundant. Then we can use that as an early warning system, particularly for the developing countries, Bangladesh, India, the Middle East, and some of the other countries of the Far East.
Q: How are satellites used to track cholera outbreaks?
Rita Colwell: It occurred to us when we were doing our studies that these massive plankton populations that have been monitored, at least the phytoplankton, by biological oceanographers, could give us a clue as to the cholera epidemics. So the satellites pass over and take photographs of the patches of plankton in the oceans. And when these patches become huge and can be detected very easily by satellite, we then correlated that by graphing the intensity of the chlorophyll measurement and then gave a time lag for the expected increase in zooplankton populations, and then a short time lag. We then found that indeed, our calculations fit, that we could predict from the chlorophyll, to the time lag, to the zooplankton blooming, populations bloom, to the cholera epidemics that occurred in Bangladesh and in India using the Bay of Bengal as our experimental laboratory, so to speak.
Q: You talked about seasonality, what did you mean?
Rita Colwell: Seasonality is a fascinating characteristic of infectious disease. We know that the summer months tend to be the times that diarrheal diseases are more frequent, and the winter months are when influenzas are more frequent. We have assumed that in the summer months, that the ingestion of contaminated food creates the problem. Now we’re beginning to understand that it’s related to the natural cycles of the organisms that are pathogenic for humans, animals, and plants. I don’t want to imply that it’s just the pathogens that have the seasonal cycles, the other microorganisms as well. Of course, the interest is trying to prevent infectious disease. So with influenza, very recently, it’s been shown that the virus that causes the flu actually is more infective at lower temperatures, more transmissible than it is at warmer temperatures. That gives us then a very good scientific explanation for the seasonality for influenza. Similarly with dengue or hantavirus, or perhaps with Lyme disease, we’re able to monitor the host that carries those infectious organisms and we find that again, this is a seasonality when the ecology of the organism is expressed by nature of the host which it is associated. We haven’t though much about this, as medical doctors, as research scientists, but now I think it’s critical for us to understand these patterns that are so intertwined with climate. If climate is changing, if the global temperatures are warming, we will see changes in the patterns of infectious disease.
Q: These patterns of disease, how are they changing?
Rita Colwell: Several possibilities come to mind. One is with longer periods of time, when the surface water temperature remains warm, that is right now, we can predict that the temperature’s warm in late March-early April, through June, July and in Bangladesh there’s a monsoon, rains come in and then there’s another peak in September-October-November. But if we have warmer temperatures persisting for a longer period of time, it may lengthen the so-called “cholera season” for Bangladesh.
But we also have to consider the extreme weather events that have been predicted and are occurring, associated with global warming. The extreme weather events can lead to a breakdown in sanitation, sewage treatment plants, water treatment systems. And indeed, because the bacteria are part of the natural environment, we could again begin to see epidemics of cholera in the U.S. and in Europe that we haven’t see in almost a hundred years.
Q: Earlier you also spoke of influenza.
Rita Colwell: Transmission has been shown to have a genetic basis, and the temperature at which the organism is exposed will influence its transmissibility from person to person. It’s more infective at colder temperatures. It’s less transmissible at warmer temperatures, which leads us to seeing the epidemics in the winter months. We had always ascribed, as epidemiologists, that is because people were crowded, living inside during the winter months. But it turns out to be a characteristic of the virus. And that I think is highly instructive, because it tells us that we need to understand the ecology of these infective agents in the natural environment as part of the environment that we humans inhabit in order to explain, understand, and prevent infectious diseases.
Q: What take-home message would you like to leave people today, on the connection of cholera with the environment?
Rita Colwell: It’s not to strike fear in the hearts of citizens, but instead to provide an understanding of these interactions that are very important, and to point out that we can now develop a predictive capacity for infectious diseases so that we can develop a preemptive medicine, that is, to know when to expect the epidemics, and to know which public health measures to institute. And it will be very cost-effective for vaccines, because we can eventually be able to predict what parts of the world, what parts of the country that one can expect the outbreaks of a given infectious disease and to use wisely and effectively, and efficiently the public health measures, such as vaccines, and other measures that can be instituted for preventing the disease.
Dr. Rita Colwell is Distinguished Professor at the University of Maryland College Park and on the faculty of Johns Hopkins University Bloomberg School of Public Health. She is also Senior Advisor and Chairperson of Canon US Life Sciences, Inc. and a Member of the Board of Regents of the Potomac Institute for Policy Studies, as well as a Former Director of the National Science Foundation.
In his years with EarthSky, Jorge Salazar conducted thousands of in-depth interviews with scientists. He knows a lot about as diverse as nanotechnology, ecosystem-based management, climate change, global health, international environmental treaties, astrophysics and cosmology, and environmental security. Jorge currently works as a Technical Writer/Editor for the Texas Advanced Computing Center, which designs and deploys powerful advanced computing technologies and innovative software solutions for scientific researchers.