Researchers Uncover Cause of Argentinian Cholera Outbreak

The current cholera pandemic, which began in the 1960s, is caused by a single epidemic Vibrio cholerae strain, called 7PET. This was discovered after a team of international researchers sequenced more than 500 cholera samples gathered through the years of the cholera outbreak.

The new sequencing analysis was done to better understand how the epidemic strain spread and to investigate the local, endemic strains that were circulating in the country during the outbreak of cholera in the year 1991-1998.

Cholera is an acute diarrheal disease caused by the toxigenic bacterium Vibrio cholerae. Forty-seven countries are currently affected worldwide, and nearly a hundred thousand people die annually due to this disease. There have been seven cholera pandemics around the globe since the 1800s resulting in the death of millions. In 1991, Argentina, a country that is free from cholera epidemic for 96 years, experienced another outbreak.

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The data gathered during the outbreak greatly influenced Argentina's health policy, as the national alert surveillance system utilized whole-genome sequencing to differentiate the pandemic and non-pandemic strains of V. cholerae bacteria. The full study can be found in Nature Communications.

Genomic Sequencing

The researchers performed genome sequencing of historical V. cholerae samples at the national reference laboratory of Argentina, INEI-ANLIS "Dr. Carlos G. Malbrán." They analyzed these to understand the disease patterns better and enable alerts in the event of a new introduction of pandemic lineages.

The bacteria did not evolve much during the six years of the epidemic, which significantly differs from the diverse, endemic strains of V. cholerae also in circulation. This previous work demonstrated how even though endemic strains can still make people ill, it does not spread as rapidly, nor can it cause an epidemic. 

The findings of this study made the researchers conclude that a single clone of the epidemic 7PET strain, which likely came from Peru, was the main culprit behind the Argentinian outbreak. Aside from that, this genetically invariable strain existed alongside more changeable endemic V. cholerae strains.  

Difference between endemic and epidemic bacteria

According to Matthew Dorman, from Wellcome Sanger Institute and first author of the study, a 7PET pandemic strain entering Latin America from elsewhere can cause massive epidemics.

It is important to differentiate the differences among local, endemic V. cholerae that coexist alongside 7PET during a cholera epidemic to control cholera epidemics efficiently.

Senior author Dr. Josefina Campos said that because of the comprehensive surveillance and reporting system in the reference laboratory in Argentina, there is a snapshot of an entire epidemic that serves as a means for a better understanding of the detailed evolution of V. cholerae bacteria in the country.

This information is crucial for disease control as it can help in the monitoring and response to any future cholera outbreaks. Argentina is the first national reporting system in the world to make use of genomic data to monitor cholera in this manner.

Professor Nick Thomson, a senior author from the Wellcome Sanger Institute, said this kind of detailed study allows a better understanding of how cholera is spreading worldwide. It provides information for better planning of strategies and identifies areas that need further research.

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