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Rising temperatures in UK waters are leading to a boom in a bacteria linked to gastroenteritis in humans, new research has found.
There has been an increase in various strains of the potentially harmful Vibrio bacteria.
Researchers led by academics from the University of Exeter also found two strains, Vibrio rotiferianus and Vibrio jasicida, which have never been recorded in the UK’s shallow waters before.
Because shellfish are filter feeders, levels of the pathogen can build to significantly higher concentrations in their tissues compared with the surrounding water.
Vibrio bacteria have been linked to mass die-offs in wild and farmed oysters, and can cause gastroenteritis in humans if raw or undercooked shellfish is ingested.
Vibrio can also cause skin infections if the bacteria enter the body through cuts and abrasions.
There has been a surge in Vibriosis infections in humans and aquatic animals in recent years, the researchers found.
Dr Sariqa Wagley, of the University of Exeter, said: “Vibrio species can often be found in UK waters in summer, when temperatures are more favourable for them.
“With sea-surface temperatures rising due to climate change, Vibrio activity in the waters is more common, and the diversity of Vibrio species is now increasing.”
The research team used Met Office data to find locations where sea-surface temperatures were reaching between 13C and 22C, which is favourable to the growth of the various Vibrio species.
They then analysed samples from four shellfish farms located in these areas, namely Chichester Harbour, Osea Island, Whitstable Bay and Lyme Bay.
Vibrio parahaemolyticus, the most common cause of seafood-borne gastroenteritis worldwide, was found at Chichester Harbour.
The strain Vibrio alginolyticus, which causes wound infection and the ear infection otitis, were found at Chichester Harbour, Osea Island and Whitstable Bay.
These three sites had sea-surface temperatures of above 18C for a number of weeks each year.
“It is important to note that thorough cooking kills harmful Vibrio bacteria in seafood,” Dr Wagley said.
“However, increasing abundance and diversity of Vibrio bacteria creates health risks not only for people eating seafood, but for those using the sea for recreation purposes – either due to swallowing infected seawater or from the bacteria entering exposed wounds or cuts.”
She continued: “Vibrio bacteria are also a threat to a variety of marine species including shellfish themselves.
“Disease costs the global aquaculture industry £6 billion a year, and this burden of disease can be devastating.
“We have not seen mass mortality of shellfish due to Vibrio bacteria here in the UK yet, but this has occurred elsewhere – including in France and Australia.”
Vibrio rotiferianus was found in four samples gathered from Chichester Harbour and Osea Island, while Vibrio jasicida was found in eight samples taken from Chichester Harbour and Whitstable Bay.
It is the first time these two strains of the Vibrio bacteria have been detected in the UK.
Dr Wagley added: “Our findings support the hypothesis that Vibrio-associated diseases are increasing and are influenced by the rise in sea-surface temperature.
“We need to monitor this situation closely, to protect human health, marine biodiversity and the seafood industry.”
Dr Luke Helmer, from Blue Marine Foundation and the University of Portsmouth added: “The impacts of climate change on the marine environment are likely to be widespread.
“Understanding how these changes will affect ecologically and commercially important species and the people that rely on them will be crucial moving forward, in order to mitigate against them.”
The UK shellfish industry was worth £350 million in 2019, according to Government data, but almost 95% of native oyster reefs have been lost.
In Chichester Harbour, the population of native wild oysters fell 96% between 1998 and 2017.
While it cannot be proven that Vibrio bacteria are behind the decline, the report’s authors emphasised that it was important to take a “one health” view of marine ecosystems.
The approach considers all environmental stressors, including sewage leaks, high concentrations of harmful chemicals and increasing numbers and strains of animal and human pathogens.
The study, The increased prevalence of Vibrio species and the first reporting of Vibrio jasicida and Vibrio rotiferianus at UK shellfish sites, is published in the journal Water Research.
The research was funded by Biotechnology and Biological Sciences Research Council (BBSRC), and was supported by Chichester and Havant Council and Sussex Inshore Fisheries and Conservation Authority.