You may want to think twice before you eat a raw oyster or dive into the ocean to escape a hot day. While microscopic, a collection of disease-causing bacteria known as Vibrio are becoming more and more abundant as climate change creates the ideal conditions for their spread and survival.
Vibriosis, the illness caused by Vibrio, is most commonly linked to two species—Vibrio vulnificus and Vibrio parahaemolyticus. Humans can contract an infection through an open wound or by consuming raw or undercooked seafood. The bacteria are shaped like a curved rod and are gram-negative, a characteristic that causes them to be highly resistant to antibiotics.
While reported cases of vibriosis are rare, with only V. vulnificus estimated as causing approximately 100 to 200 U.S. cases per year, the actual number is likely higher as mild infections are hardly ever tested.
“The majority of people are going to note the type of wound and the look of their infection, and they’re going to scrub it, they’re going to treat it appropriately with some sort of disinfectant, and they’re going to make sure that Vibrios do not take root in a serious infection,” University of North Carolina Chapel Hill professor and environmental microbiology researcher Dr. Rachel Noble says.
“Florida has been a hotspot for Vibrio infections for quite a while now. But there’s been sporadic cases of Vibrio infections occuring further north along the Atlantic coastline.”Elizabeth Archer, Ph.D., University of East Anglia in Norwich, U.K.
Serious V. vulnificus infections resulting in hospitalization or death are more likely in males over 50 years old, those with liver cirrhosis, diabetes, and the immunocompromised. However, scientists have identified Vibrio as a “barometer of climate change” and expect infections to become more widespread. The bacteria tend to thrive in warm brackish water, which is saltier than freshwater but less so than seawater. This environment occurs in estuaries, such as the Chesapeake Bay, where rivers and streams meet the ocean. Due to global warming and increased extreme weather events, sea temperatures are rising and salinity levels are decreasing, creating ideal conditions for Vibrio.
In March 2023, researchers from the University of East Anglia (UEA) in Norwich, U.K. published an article in the journal Scientific Reports that showed cases of V. vulnificus wound infections have already increased eightfold between 1988 and 2018, and are now regularly reported as far north as Philadelphia.
“Florida has been a hotspot for Vibrio infections for quite a while now. But there’s been sporadic cases of Vibrio infections occurring further north along the Atlantic coastline,” the leading author of the study and Vibrio researcher Elizabeth Archer claims.
The scientific team behind the Scientific Reports article developed an ecological niche model to predict an increased geographical presence of V. vulnificus infections on the Eastern U.S. coastline. The model found that the coastline where V. vulnificus infections are present will increase by over 1000 km by the mid-21st century, translating to a doubling of cases.
“We built this model based on the existing distribution of the infections and used that to project into the future where we might find these infections,” Archer explains.
In their analysis, the researchers considered changes in air temperature, which corresponds to sea surface temperature, as well as population shifts to coastal regions. The predictive model, which included scenarios of varying emissions and global warming, showed that V. vulnificus infections may be present in every state in the Eastern U.S. by the end of the century if climate change is not mitigated.
“The expansion of infections is limited under the lower emissions scenario, which is an incentive to stop climate change,” Archer explains.
Vibrio can also infect humans through consuming shellfish. Consumers risk contracting V. parahaemolyticus, which causes a gastrointestinal infection, when eating raw or undercooked oysters.
“Shellfish concentrate those Vibrios by sometimes a hundredfold to a thousandfold,” Noble says. “They’re like a little Vibrio bomb.”
New regulations, however, show promise in limiting V. parahaemolyticus exposure and infection. States including New York, Massachusetts, and Washington have enacted Vibrio Control Plans that regulate how shellfish must be handled after harvesting. For example, oysters harvested during the summer must be immediately refrigerated and cannot be left in standing water.
“The plan also gives them a mechanism to kind of track the Vibrio infections,” Noble says.
Recent news coverage, particularly in response to the March 2023 article in Scientific Reports, has drawn attention to the presence of Vibrio in oceans and shellfish.
“Our media lately has kind of taken off on the relative importance of Vibrio infections. But compared to other foodborne pathogens, Vibrio infections are extremely rare,” Noble reports. “If you do not fall into those categories of higher risk, I would say that shellfish are a fantastic food.”
According to Archer, it’s difficult to find the balance between inciting fear and educating the public on the risk of Vibrio.
“You don’t want to terrify people and make them feel like they can’t go in the sea, but you also want them to be aware of the risk,” she says. “What’s more important to me is the wider understanding that our health is connected to the planet’s health.”
- Vibrio are a collection of microscopic,disease-causing bacteria
- Vibriosis, the illness caused by Vibrio,is on the rise
- Scientist believe the rise in infections is due to warming waters as a result of climate change
Archer, E.J., Baker-Austin, C., Osborn, T.J. et al. “Climate warming and increasing Vibrio vulnificus infections in North America.” Sci Rep 13, 3893 (2023). https://doi.org/10.1038/s41598-023-28247-2.
Baker-Austin, Craig et al. “Non-Cholera Vibrios: The Microbial Barometer of Climate Change.” Trends in microbiology vol. 25,1 (2017): 76-84. doi:10.1016/j.tim.2016.09.008
Interview with Elizabeth Archer. Interview by Nora Pierce. August 7, 2023.
Interview with Dr. Rachel Noble. Interview by Nora Pierce. August 17, 2023.
Vezzulli, Luigi, et al. “Climate influence on Vibrio and associated human diseases during the past half-century in the coastal North Atlantic.” Proceedings of the National Academy of Sciences, vol. 113, no. 34. August 8, 2016.
“Vibrio Vulnificus.” Cleveland Clinic. Last modified April 8, 2023.
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Nina Lichtenberg is a Science Writer at the National Institutes of Health (NIH), where she writes press releases and news features about biomedical research discoveries.
Rachel Noble, Ph.D. is a professor of marine sciences in the Department of Earth, Marine and Environmental Sciences at the University of North Carolina at Chapel Hill. She leads the research program in the Noble Lab focused on environmental microbiology and marine microbial food webs. Dr. Noble researches water quality and pathogens in water, at the intersection of the environment and public health.
Elizabeth Archer is a Ph.D. student at the University of East Anglia in Norwich, U.K. Her research is focused on the environmental conditions that influence the geographic distribution of human Vibrio pathogens in marine ecosystems and on identifying areas of elevated future Vibrio infection risk under different climate change scenarios.