Seafood harvested from warm waters is popular around the world, whether as an essential part of a daily diet or a special treat. But eating such dishes can lead to tingling and numbness in fingers and toes, nausea, abdominal pain, a burning sensation upon touching something cold and even poisoning.
Each year, some 500,000 consumers around the world are affected by ciguatera poisoning from large fish such as barracuda, moray eel, snapper and grouper. The culprit—ciguatoxin—lurks in algae that the fish eat. It's a hidden threat, though, because it does not harm fish but is toxic to humans who eat them.
While the toxins responsible for ciguatera poisoning are known to occur in the Caribbean Sea, the Indian Ocean and the Pacific Ocean, they have more recently been found in the Canary Islands, the eastern Mediterranean Sea and the western Gulf of Mexico. The algal source of ciguatoxins in the Pacific region was identified years ago, but the source in the Caribbean was not, despite nearly 30 years of research on the topic.
In 2023, the hunt for the Caribbean producer of ciguatoxin ended when scientists from the National Research Council of Canada (NRC) and collaborators from the United States and Norway found the needle in the haystack. After years of painstaking algal collection and analysis, they focused their efforts on species collected in waters surrounding the US Virgin Islands. NRC researchers finally identified the novel algal ciguatoxin and then worked with collaborators to demonstrate metabolism in fish species associated with ciguatera poisoning.
According to Pearse McCarron, who leads the team at the NRC's Biotoxin Metrology Group, this is groundbreaking research in the field. "The findings will make it possible to develop methods and standards to help food safety laboratories monitor and manage ciguatera," he says. "And that will go a long way toward dealing with the problem and hopefully preventing the illness in humans."
A sea of research
"We have an extensive history of successful research on toxins produced by algae but, until recently, have not tackled certain compound classes, including ciguatoxins," adds Pearse. In 2018, fortunately, the NRC was able to launch a concerted effort to conduct research to address this huge global problem.
An important first step in the project was getting involved in a collaborative project on ciguatoxins with experts at the University of South Alabama, the University of Texas at Austin, the University of the US Virgin Islands and the Norwegian Veterinary Institute.
The US teams collected algae samples from coral reefs in the Caribbean, established cultures to grow algae and then screened them for toxicity. The NRC performed the chemical profiling and identification that determined the structure of the toxin. Norwegian researchers conducted enzyme incubation experiments to confirm that the algal toxin transforms into the toxin found in fish.
Research Officer Elizabeth Mudge, a specialist in food science and chemistry, joined the NRC at the outset of the project and, along with the NRC's Chris Miles, took the lead in applying advanced measurement science approaches to the investigation. When the toxic strains were received from collaborators, the researchers used high-resolution mass spectrometry along with innovative chemistry techniques to characterize the algae's chemical profile. And from that came the "aha" moment when the unknown ciguatoxin was identified.
"Our varied approach and multidisciplinary team led to this breakthrough," says Elizabeth. "The findings, published in an article in the journal Chemosphere, will make it possible to develop methods to understand the distribution of these toxins in the food web and ultimately help establish monitoring programs to protect consumers." And this will contribute greatly to food safety.
Better food safety tomorrow
Pearse says the NRC will continue working collaboratively to develop next-generation metrological tools for managing the issue. It will also work with collaborators to create certified reference materials that testing and research labs in Canada and around the world can use to measure for these toxins.
"This multidisciplinary team approach brought together the skill sets and capabilities of the Biotoxin Metrology team and collaborators to solve a problem that had eluded researchers for decades," Pearse concludes. A good formula for success!