A new University of Maryland-led, international study shows that over the past half century there has been a clear correlation between warming of North Atlantic waters, increasing numbers of Vibrio bacteria in those waters, and rising numbers of people along U.S. and European North Atlantic coasts who have become infected by pathogenic Vibrio bacteria – including species that can cause life-threatening infections.
In a paper published online on August 8, 2016, in the journal Proceedings of the National Academy of Sciences (PNAS), University of Maryland Distinguished University Professor Rita Colwell and co-authors from Italy, Britain, and Germany write that: “The evidence is strong that the ongoing climate change is influencing outbreaks of Vibrio infections on a worldwide scale.” However, they say that to their knowledge theirs is the first study to provide evidence linking decades of climate warming, Vibrio abundance and Vibrio-associated disease.
“It will come as a surprise to the public to know that there is this direct connection between the oceans and human health, with respect to infectious disease,” said Colwell, who has studied cholera for nearly 50 years and has written more than 750 publications. A former director of the National Science Foundation and former president of the American Association for the Advancement of Science, Colwell is currently a distinguished university professor at the University of Maryland and the Johns Hopkins University’s Bloomberg School of Public Health, a member of the National Academy of Science, and Chairman and Global Science Officer of CosmosID, Inc.
Vibrio bacteria are found in large numbers among the small and microscopic organisms that constitute marine plankton. There are more than 100 Vibrio bacteria species that can cause disease in animals, with about a dozen that are human pathogens. Cholera, an acute diarrheal infection caused by ingestion of food or water contaminated by Vibrio cholerae, is responsible for an estimated 3–5 million illnesses and more than 100,000 deaths every year, according to the World Health Organization.
In the United States, the CDC estimates that 80,000 people become sick from vibrio infections and 100 die from their infection every year. Some Vibrio species, such as Vibrio vulnificus, can get into the bloodstream. Half the people who get a Vibrio vulnificus infection die, sometimes within a day or two of becoming ill, others survive only after having limbs amputated.
Uncovering Vibrio data in 50-year-old samples
Because there was little existing data on ocean microbes covering the time and geographical scales needed for their study, the team developed a novel, technically challenging approach to studying the long term changes in the populations of Vibrio bacteria. Their approach took advantage of the Continuous Plankton Recorder, one of the most geographically extensive and longest time duration archives of marine biological samples. However, using this archive required the team to overcome the formidable challenge of recovering testable DNA from formalin-fixed samples of plankton that ranged from recently collected to more than 50 years old. Molecular analysis of these DNA samples was then conducted to find and identify types and amounts of Vibrio bacteria present.
The researchers analyzed 133 samples collected during the past half-century at nine locations: northern North Sea, southern North Sea, western English Channel, Iberian coast, Iceland coast, Irish Sea, Newfoundland, Nova Scotia, and the North Atlantic.
The team’s groundbreaking analysis is par for the course, for Colwell, a microbiologist, whose work bridges many other areas, including ecology, infectious disease, public health, computer and satellite technology and international diplomacy. She has made a career of novel approaches and outside-the-box thinking. Previous breakthroughs include her research showing that plankton comprises an environmental reservoir for human Vibrio cholerae infection via contaminated drinking water. This finding blew apart the then conventional wisdom that cholera was spread only by person to person contact. Her development of the first model to apply remote satellite imaging to track and predict outbreaks of cholera before they occur became a prototype for infectious disease monitoring and prevention around the world.
Climate influence on Vibrio and associated human diseases during the past half-century in the coastal North Atlantic, Luigi Vezzulli, Chiara Grande, and Carla Pruzzo, University of Genoa; Philip C. Reid, Pierre Hélaouët, and Martin Edwards, Sir Alister Hardy Foundation for Ocean Science; Martin Edwards, University of Plymouth; Manfred G. Höfle and Ingrid Brettar, Helmholtz Centre for Infection Research, Rita R. Colwell, University of Maryland and Johns Hopkins Bloomberg School of Public Health.