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  • Writer's pictureP.K. Peterson

Vibrio vulnificus: It Likes It Hot

“He was a bold man that first ate an oyster."

- Jonathan Swift


V. vulnificus causes more than 95% of seafood-related deaths.”

- Kristin Walter, MD, MS, pulmonary specialist



In early August, the report “Bacteria in Long Island Sound prompts warning from health officials,” in the Hartford, Connecticut Eyewitness News caught my eye. It piqued my interest because the bacterial pathogen—Vibrio vulnificus—is rarely seen that far north in U.S. seawater. (No V. vulnificus infections were recorded in Connecticut over the previous two summers.) In this Germ Gems post, I describe the nature of V. vulnificus infections and tell why they are such a scary harbinger of the impact of global warming on our oceans.

What is V. vulnificus and where is it found? V. vulnificus is a gram-negative bacillus belonging to the Vibrionaceae family. (Vibrio is derived from the Latin “to wiggle or vibrate” [a property of its flagellum], and vulnificus is from the Latin “to wound.”) This bacillus is found worldwide and causes gastrointestinal disease, wound infections, and highly lethal septicemia.


Like the two other Vibrio species (V. cholera and V. parahaemolyticus), V. vulnificus is a member of salt water marine environments, such as estuaries, deltas, shorelines as well as deeper ocean surfaces. It takes up residence in the stomachs of shellfish (mainly oysters) and the intestines of fish. V. vulnificus is both a waterborne and foodborne pathogen. The bacilli infect humans either through the ingestion of contaminated seafood or by direct wound contact with contaminated water. (I have featured V. vulnificus in several earlier Germ Gems articles, for example, my March 14, 2021 post, “Water, Water Everywhere, but Is It Safe to Drink?”)


In the U.S., V. vulnificus favors the warm coastal waters of the Gulf of Mexico and off the state of Florida. Approximately, 100 cases of V. vulnificus infection are reported each year in the U.S., a number that is steadily increasing in recent years.


Clinical presentations. The three distinctive clinical presentations of V. vulnificus infections are: primary septicemia; primary wound infections; and primary gastroenteritis. Ingestion of the bacilli contaminating raw shellfish can result in the primary septicemia syndrome, which can rapidly proceed to dramatic extremity involvement with necrotic (gangrenous) bullae or ulcers, thus its description as a “flesh-eating bacteria.” The overall death rate for this presentation is 50%.

Introduction of bacilli into cuts or other skin lesions can result in primary wound infections, which rapidly progress to necrotizing fasciitis (a form of gangrene) requiring extensive surgical removal of dead tissue. The overall mortality for primary wound infections is about 25%. Gastrointestinal disease is manifested by vomiting and diarrhea and is less fatal (about 10% of cases).


Who’s at risk of severe disease? Conditions that are known to increase the risk of severe V. vulnificus infections are: liver disease (cirrhosis), cancer, HIV infection, diabetes, and immunosuppression. Delayed diagnosis and treatment also increase the risk of dying.


Diagnosis is established by culturing blood, stool, or wounds. Broad spectrum antibiotics should be administered as soon as the index of suspicion is raised of V. vulnificus infection. (An added nasty feature of this bacillus is that 50% of isolates are resistant to multiple antibiotics.)


Prevention of infection. Food-related V. vulnificus infection can be prevented by not eating raw or undercooked seafood and by use of gloves plus handwashing after handling raw shellfish. Avoiding contact with brackish saltwater is a must for anyone with a cut or open wound.


The biggest challenge to prevention, however, is global warming. The effect of global warming has been correlated both with an increasing prevalence and virulence of V. vulnificus. As water warms, oysters increase their siphoning activity, thus enhancing their chances of picking up bacilli. (This is the basis for the recommendation to avoid eating raw oysters especially during months that don’t contain a “r.”)

What’s the impact of marine heat waves? Although support is growing for measures that limit greenhouse gas emissions, so too are the challenges growing bigger. For example, this past July was the hottest on record for our planet. And currently, we’re witnessing the catastrophic loss of lives and property on the Hawaiian island of Maui caused in part by a combination of drought-parched landscapes and strong mountain winds brought by Hurricane Dora.


In a July 14, 2023 article by the National Oceanic and Atmospheric Administration (NOAA) entitled “The ongoing marine heat waves in U.S. waters, explained,” we’re informed that NOAA scientists have tracked a steady climb in ocean temperatures since April, 2023 that are responsible for a dramatic increase in “marine heat waves” impacting marine ecosystems, especially off the coast of Southern Florida.


We have been warned about the impact of marine heat waves on marine ecosystems before. In his article “Climate Change and the Occurrence of Harmful Microorganisms in Florida’s Ocean and Coastal Waters,” the late Karl Havens, a professor at the University of Florida, summarized the diverse impacts of climate change-related ocean warming on microbial life in oceans. He wrote:


"Climate change is expected to result in increased temperatures of nearshore ocean water, and this could lead to increased growth of harmful microorganisms. These include algae that form noxious or toxic blooms, including red tides, and bacteria and other pathogens."


It appears that V. vulnificus isn’t the only pathogen that “likes it hot.”

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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