Cholera is a severe diarrheal sickness caused by a Vibrio cholerae bacterial infection of the intestine. People can become ill if they consume cholera-contaminated food or water. The infection is frequently minor or without symptoms, although it can occasionally be severe and life-threatening. According to scientists, regular monitoring of the cholera bug genome is critical for averting outbreaks of new varieties.
A new study explains why a highly infectious version of the cholera bug that produced huge illness outbreaks in the early 1990s did not create the feared eighth cholera pandemic but instead vanished.
The researchers examined samples of O139 Vibrio cholerae, a cholera-causing bacteria variety, and observed significant changes in its genome over time that contributed to its unexpected drop. These genetic modifications led to a gradual loss of antimicrobial resistance (AMR) and a shift in the toxin types generated by the cholera bug. These alterations, taken together, are most likely to blame for O139’s inability to spawn the eighth cholera pandemic.
The cholera bug is not currently being closely examined. Continuous monitoring of the genes underpinning AMR and toxin production, according to scientists, is critical to staying ahead of the cholera bug as it evolves. In particular, this will help to plan changes to vaccines and appropriate public health responses to prevent future cholera outbreaks.
There’s a real possibility that another cholera variant may emerge with the potential to cause large outbreaks, which could lead to the eighth cholera pandemic. Continuous surveillance of the variants in circulation is our best chance of preventing mass outbreaks.
Dr. Ankur Mutreja
In 1992, the O139 variety of Vibrio cholerae was discovered in India. It swiftly surpassed the previous O1 type, causing massive disease epidemics in India and Southern Bangladesh.
Scientists were astonished by the quick spread of O139 across Asia, as they anticipated it might cause the eighth cholera pandemic; as a result, cholera vaccines were adjusted accordingly. But, for whatever reason, the pandemic never occurred: by 2015, the variety had significantly diminished, and the O1 variant had re-established itself as the dominant strain. Scientists haven’t figured out why until now.
The study is published today in the journal Nature Communications.
“There’s a real possibility that another cholera variant may emerge with the potential to cause large outbreaks, which could lead to the eighth cholera pandemic. Continuous surveillance of the variants in circulation is our best chance of preventing mass outbreaks,” said Dr. Ankur Mutreja, in the University of Cambridge’s Institute of Therapeutic Immunology and Infectious Disease, senior author of the study.
Cholera is a potentially fatal infectious disease that is mainly contracted by eating or drinking contaminated food or water. It primarily produces big outbreaks in areas with low hygiene and sanitation, hence it is mostly found in underdeveloped countries.
Cholera can also occur when water and sewage systems are disrupted as a result of conflict or natural disaster. According to recent news sources, the Ukrainian city of Mariupol, which has been nearly decimated by weeks of Russian shelling, is now at risk of a massive cholera outbreak.
In the past 200 years, seven cholera pandemics have killed millions of people across the world; the seventh is still ongoing with large outbreaks in Yemen and Somalia. The dominant variant of Vibrio cholerae, the bacteria that causes cholera outbreaks today, is called O1 and arose in the 1960s — replacing all pre-existing variants.
The new study analysed 330 samples of the cholera variant O139, taken between 1992 and 2015, to reveal two key changes in its genome that may have been the cause of its decline over three overlapping waves of disease transmission.
Prior to the appearance of the O139 strain, cholera was resistant to a wide range of medications. However, O139 was resistant to them, which is likely why it quickly became the prevalent variant. The study discovered that O139 began with numerous genes that conferred antibiotic resistance. However, it eventually lost these genes over time. At the same time, the O1 variant developed antibiotic resistance.
“The O139 type of cholera exhibited antibiotic resistance when it initially appeared. However, this resistance wore off with time, whereas the pre-existing O1 variety gained resistance and re-established itself” Mutreja stated.
