A deadly bacterium is creeping up the US east coast. How worried should we be?
Warming ocean waters are priming beaches and raw shellfish for Vibrio even as scientists are trying to stay one step ahead
Originally published by Grist
By Zoya Teirstein
Bailey Magers and Sunil Kumar cut strange figures on Pensacola Beach. Bags of disinfectant solution surrounded them on the white sand; their gloved hands juggled test tubes while layers of rubber and plastic shielded their skin from the elements. As the two organized their seawater samples on the popular Florida shoreline last August, an older woman wearing a swimsuit walked over to ask what they were doing.
“We’re just actively monitoring water quality,” they told her, but she pressed on.
“Are you looking for that flesh-eating bacteria?”
“We’re looking into it,” they replied, hoping not to frighten her. The woman turned back toward the ocean, her curiosity satisfied. As she walked away, Kumar noticed that she had scrapes and bruises on her body. A few minutes later, he watched her step into the waves. He shook off a chill and returned to the task at hand.
Magers and Kumar study a bacterium called Vibrio, part of a lineage of ancient marine species that likely emerged sometime around the Paleozoic era. Researchers think there are more than 70 Vibrio species in the environment today, hundreds of millions of years later. The organisms float in warm, brackish water, attaching themselves to plankton and algae and accumulating in prolific water-filtering species such as clams and oysters.
A small number of Vibrio species can sicken and even kill. In worst-case scenarios, a person who has been exposed to the most dangerous of them – by swimming in brackish water with an open wound or ingesting a piece of raw shellfish that is contaminated with the toxin – may find themselves with only hours before the flesh on one or more extremities starts to bruise, swell and decay. Without the quick aid of powerful antibiotics, septic shock can set in and lead to death. Anyone can get infected, though it is much more likely in people who have liver disease or are immunocompromised, elderly people or people who are diabetic.
A first warning signal
The climate crisis is making the world’s oceans, which have absorbed more than 90% of the excess heat trapped by greenhouse gas emissions, more hospitable to Vibrio. Research shows temperature and salinity are the largest predictors of how widespread Vibrio bacteria are. As water temperatures rise, so does the concentration of Vibrio in seawater – boosting the risk of infection for beachgoers and shellfish consumers. The bacteria start getting active in water temperatures above 60F and multiply rapidly as coastal waters warm throughout the summer.
In recent years, scientists have documented Vibrio expanding into places that were once too cold to support the bacteria, pushing as far north along the US east coast as Maine and appearing with more prevalence in temperate seas around the world.
Vibriosis infections in general are the leading cause of shellfish-related illness in the US They have increased “more than any other illness caused by a pathogen in the US food supply” since the Centers for Disease Control and Prevention, or CDC, started keeping tabs on such illnesses in 1996, according to a 2019 analysis by the International Association for Food Protection. The report attributed the precipitous rise to a “perfect storm” of factors that include the climate crisis, food handling practices, expanding globalization, a patchwork of regulatory oversight and improved diagnosis.
On their conspicuous expeditions to Pensacola and other Sunshine state beaches, Magers and Kumar are trying to understand where, and when, harmful Vibrio species are present across the state. The research they’re doing is part of an ongoing effort by a laboratory at the University of Florida to create a Vibrio early warning system for the eastern US – a program that can alert public health departments to high Vibrio concentrations in any given area a month in advance.
How many limbs would be saved, Magers wonders, if doctors and nurses could be warned ahead of time that their emergency rooms would soon see an uptick in these chronically underdiagnosed infections?
The work serves more than one purpose: as Vibrio bacteria spread north into cooler waters, they serve as a first warning signal of changing marine conditions – giving researchers a heads-up that the familiar composition of marine species in their local waters may be starting to shift. In Europe’s Baltic Sea, for example, a spike in Vibrio infections in July 2014 closely mirrored a heatwave that rapidly warmed the shallow sea.
The incident showed researchers that Vibrio spikes herald unusually warm marine conditions – and they have since been utilized as barometers for ocean heatwaves and sea-surface warming patterns, not just food safety.
