Hurricanes, heat waves, floods, and fires – the incidence of these natural disasters have risen alongside the global temperature. But flesh-eating bacteria? That might have been missing from our climate change bingo sheet.
Vibrio, the bacteria being used as a “barometer of climate change”.
A lesser-known consequence of global warming is the rise of Vibrio species and the life-threatening illness they can cause. Vibrio are Gram-negative, rod-shaped bacteria that live in saltwater. They are found on the coasts of North America, where they thrive during warmer months (May to October). Multiple species can cause human illness through entering open wounds and the consumption of raw or undercooked seafood like oysters. Most notably, Vibrio cholerae is remembered as the cause of the cholera pandemics throughout the 19th century. Now, foodborne illnesses like cholera are rare in the US and other industrialized parts of the world. They are also easily preventable and treatable with common antibiotics like doxycycline.
Other vibrio species pose a greater public health threat and cause more severe illness. The most pathogenic species, Vibrio vulnificus, can cause necrotizing wound infections that result in amputations in 10% of all cases. Thus, it is often referred to as a flesh-eating microbe. Therefore, it is worrisome that a recent study mapping historic V.vulnificus infections has demonstrated that these infections have been increasing over time and spreading.
The study, “Climate warming and increasing Vibrio vulnificus infections in North America”, published in Scientific Reports, examines the impact of climate change on V.vulnificus infections across the Atlantic coastline over the past 30 years. Vibrio was once contained to more subtropical regions of the US like the southeast. However, now bacteria have been found inhabiting regions in the north like the Philadelphia coast.
The expansion of this harmful bacteria has had grave repercussions for human health.
Currently, V.vulnificus illnesses are rare but they have high mortality rates. According to the CDC, one in five people with a wound infection die within 48hrs of contracting the bacteria. V. vulnificus infections have increased from 10 cases per year in 1988 to 80 in 2018. The indigence of these infections has also spread up the coast during these 3 decades. The study estimates that this will continue to increase, with 200 cases per year by the end of the century. The majority of this change is attributed to climate change. Using multiple climate models, they also predict that should temperatures continue to rise, the bacteria would be able to colonize the coast lines of New York. Ultimately, how far the bacteria will spread will largely depend on how effective our climate change mitigation efforts are.
Not only has Vibrio survived during this era of climate change, but it has thrived.
Vibrio species were also identified on seaweed blooms. As the ocean gets warmer, seaweed rapidly grows, forming seaweed blooms. Since 2011, a large abundance of brown seaweed, known as sargassum, has grown from every spring to summer. As of March 2023, it is the largest it’s ever been. At roughly 5,000 miles wide and twice the width of the US, the floating mat of seaweed is known as the Sargasso Sea and can be seen from space.
Dispersed, sargassum is not harmful. The seaweed serves as a source of oxygen and a habitat for local marine life like sea turtles, but in large masses they endanger ecosystems by blocking sunlight for crucial for coral and vegetation on the sea floor. These large seaweed islands can also wash up on shore. Rotting Sargasso releases sulfide gases which smell like rotten eggs. Tourism concerns aside, a recent study identified multiple vibrio species on Sargasso seaweed. These findings were shared in “Sargasso Sea Vibrio bacteria: Underexplored potential pathovars in a perturbed habitat”, published in Water Research.
Furthermore, the Sargasso Sea is contaminated with plastic. This plastic is also home to vibrio. Multiple vibrio species were identified on samples collected from the Caribbean and Sargasso Sea. In the past, it was suggested that this occurs based on research examining microplastic, but this is the first study to provide evidence that this phenomenon occurs in the wild.
Vibrio is normally known to adhere to shellfish and other seafood. Researchers of the study demonstrated that the bacteria readily adhere to plastic debris. This ability to attach is important when it comes to establishing disease. Genomic analysis also revealed the presence of genes to produce toxins. Altogether, this suggests that Vibrio bacteria have adapted to ocean pollution and rising temperatures in ways that can have harmful consequences for human health.
How real is the threat of Vibrio?
Multiple articles from the past week have announced that patches of the Sargasso Sea have washed up on Florida’s shores. Hitchhiking upon that seaweed? Unsurprisingly, no vibrio. Despite headlines suggesting otherwise, V. vulnificus has not been detected on these sargassum samples. A “pathogen storm” or vibrio “pandemic” is also not imminent. Vibrio infections are still rare and not contagious. While Florida officials do not regularly test the seaweed, it is recommended that beach-goers be cautious and keep their distance. Seaweed blooms host other dangers, including toxins that get released as the vegetation rots on shores. Therefore, read news of “flesh-eating bacteria” with a grain of salt.