SEOUL, KOREA - Researchers have used next generation gene sequencing to trace the source and explain the spread of the current global cholera pandemic. The study1, published in the August edition of the journal Nature, reveals that the particular cholera type responsible for the current pandemic including recent outbreaks in Zimbabwe and Haiti can be traced back to an ancestor strain that first appeared 40 years ago in the Bay of Bengal. From this ancestor, cholera has spread repeatedly to different parts of the world in multiple waves.
The team, including Dr. Dong Wook Kim, a scientist at the Seoul, Korea-based International Vaccine Institute (IVI) and Prof. Jongsik Chun at Seoul National University, co-authors of the study, tracked the spread of the organism by analysing the genomes of the causative bacterium Vibrio cholerae taken from 154 patients across the world over the last 40 years. Using the ability to track single DNA changes in the genome of this strain, they were able to map the transmission routes of the bacteria, aiding future health planning and enabling ‘backtracking’ of the disease to its origin.
These findings provide an understanding of the mechanisms behind the spread of cholera – a diarrhoeal disease that affects 3 million to 5 million people worldwide and claims more than 100,000 deaths each year, mainly in the poorest regions. Cholera claimed nearly 5,000 lives and sickened almost 300,000 people in the aftermath of the Haitian earthquake in 2010.
The analysis shows that there was not a simple single spread of a strain of Vibrio cholerae out from the Bay of Bengal. The study suggests that there have been at least three waves of intercontinental spread of cholera originating from a common strain that had emerged in the 1950s. These movements are strongly correlated with human activity, suggesting that the strain has been carried by human travel.
IVI scientist Dr. Dong Wook Kim said, “This study is among the first to link genetic information with emergence of new strains of Vibrio cholerae and uses specific changes in the genome of these strains to retrospectively track the global evolutionary spread of cholera”.
“This goes against previous beliefs that cholera always arises from local strains”, said Dr Julian Parkhill from the Wellcome Trust Sanger Institute and senior author of the study.
“These findings in due course will lead us to understand why cholera pandemics began in Southeast Asia and then spread as a wave across the world”, explained Dr Balakrish Nair, Director of the National Institute of Cholera and Enteric Diseases in Kolkata, India.
“These findings are opening up new pathways for scientists to track the migration of a communicable disease and trace it back to its roots”, added Dr Cecil Czerkinsky, Deputy Director General for Laboratory Science at the IVI.
1Mutreja A, Kim DW, Thomson N et al. (2011) Evidence for several waves of global transmission in the seventh cholera pandemic. Nature published online 24 August 2011 doi: 10.1038/nature10392
This work was supported by the Wellcome Trust, support from the Governments of Korea (Ministry of Education, Science and Technology and Ministry of Knowledge Economy) and Sweden (Sida), and support from individuals from the National Research Foundation of Korea, the Alborada Trust and Science & Technology Directorate, Department of Homeland Security, U.S.A.
The International Vaccine Institute (IVI) is the world’s only international organization devoted exclusively to developing and introducing new and improved vaccines to protect the world’s poorest people, especially children in developing countries. Established as an initiative of the United Nations Development Programme in 1997, the IVI operates as an independent international organization under a treaty signed by 40 countries and the World Health Organization. The Institute conducts research in more than 20 countries of Asia, Africa, and Latin America on vaccines against diarrheal infections, bacterial meningitis and pneumonia, as well as Japanese encephalitis and dengue fever, and develops new and improved vaccines at its headquarters in Seoul. For more information, please visit: www.ivi.int