Danger beneath the surface: How climate change has expanded the geographical range of waterborne pathogens

It’s the Fourth of July in Boston, and residents seek respite from the urban heat island inferno. The commuter rail offers a great escape: the ocean. Just a short train ride away residents can cool down on the North Shore, lay on the hot sand, and settle into a favorite beach read. But a faraway memory from childhood creeps into the mind, disrupting the dreamy lull of the waves. The faint, eerie notes of the “Jaws” soundtrack begins playing, “dunnn dun duuuunnnn duun… duuunnnnnnnn dun…” Anxiously scanning the horizon, they fail to consider that the threat could be invisible to the human eye. 

Tiny, pathogenic bacteria capable of causing serious human infections drift hidden and unseen within the waves. Among these hidden threats are Vibrio bacteria, a class of bacteria found in warm coastal waters. About a dozen species and strains of Vibrio can cause a human infection known as vibriosis. 

Humans come into contact with these waterborne pathogens when consuming raw or undercooked shellfish, or when open wounds are exposed to contaminated water. The symptoms associated with exposure to Vibrio bacteria can include wound infection, body aches, fever, chills, nausea, blood poisoning, and inflammation of the stomach lining. The severity of these symptoms range from mild to severe, depending on the nature of the exposure and whether the infected person is immunocompromised.

Over the past 40 years, infection rates and the geological range in which they occur have increased. In the eastern United States, the frequency of infection increased eightfold from 1988 to 2018. These cases were identified, on average, 48 kilometers further north on the coast than in previous years. The expansion in cases and range is a result of warmer ocean temperatures in the area. 

Warming temperature isn’t the only way climate change is increasing Vibrio infections. More frequent and extreme weather events, like coastal floods and hurricanes, push seawater containing marine pathogens further inland to areas that don’t typically contain these pathogens. This expansion places more people at risk for Vibrio infections. 

Since Vibrio and other waterborne pathogens are directly related to the symptoms of climate change, some researchers have classified these bacteria as a “microbial barometer of climate change.”

Researchers are working to better understand how the effects of climate change will influence these trends. A team at the University of East Anglia conducted a study on how climate warming impacts trends in Vibrio vulnificus infections. The researchers employed different climate warming scenarios to predict the geographical range of the pathogen over time. 

The climate warming scenarios, Shared Socioeconomic Pathways (SSPs), model different outcomes for different levels of greenhouse gas emissions. They analyzed two climate warming scenarios, SSP126 and SSP370. SSP126 is the optimistic climate warming scenario, where carbon dioxide emissions are regulated below two degrees Celsius, and SSP370 represents a warming scenario on the medium–to–high end of future emissions and temperature increases. 

Within the 2081 to 2100 time period, the two models show the geographical range of Vibrio diverging from the other model. Under SSP126, V. vulnificus doesn’t extend north of the East Coast. However, under SP370, the range of the pathogen is predicted to reach all of the East Coast states. Under both scenarios, the geographical range of V. vulnificus increases, and more people will be exposed to the pathogen.

Elizabeth Archer, the lead author of the study, notes, “this is showing the interconnectedness of our health and ocean health.” There is a need to monitor and manage the risks associated with the increased presence of V. vulnificus in coastal regions.