More than a cough: New study shows red tide exposure can cause neurological woes

A new study by Sarasota's Roskamp Institute shows breathing red tide toxins can  cause neurological problems.

Eating red tide-tainted seafood has long been known to make people sick, just as being near water with blooms can cause sneezing, coughing and a raw-feeling throat, but this is the first time published, peer-reviewed research has suggested toxins produced by the saltwater algae can trigger brain and nervous system illness in some people.

Red tide blooms are caused by the saltwater microorganism Karenia brevis. In high enough concentrations, they can stain the water a rusty auburn, devastating wildlife and the economy, as happened In 2018, when a bloom coupled with inland cyanobacteria lingered for months.

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Airborne red tide exposure

More than 250 volunteers from Lee, Collier, Charlotte, Sarasota and Manatee counties helped with the Roskamp study, published this month in the peer-reviewed journal Harmful Algae.

It provides new evidence that airborne red tide exposure can cause symptoms previously only associated with eating contaminated seafood: headaches, extreme fatigue and a peculiar hot and cold sensation reversal, said the paper's lead author, Roskamp research scientist Laila Abdullah

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The institute focuses on causes and potential cures for neurodegenerative and neuropsychiatric disorders such as Alzheimer’s disease, multiple sclerosis and Gulf War illness, leading to new treatments being clinically tested in Europe and the U.S. For this study, it partnered with the Gulf of Mexico Coastal Ocean Observing System, which is funded with a $400,000 federal grant.

"It's not surprising that a potent neurotoxin like brevetoxin could have neurological effects on people and that chronic inhalation exposure can lead to more symptoms similar to neurotoxic shellfish poisoning," Calusa Waterkeeper John Cassani wrote in an email. "During our 2018 study by James Metcalf and collaborators, we also detected the neurotoxin BMAA and two of its isomers in the water. Our recent study of aerosolized cyanotoxins also resulted in the detection of BMAA and two of its isomers. So it is possible to have exposure to multiple neurotoxins through inhalation during major red tide blooms."

More virulent blooms caused stronger reactions in the volunteers, researchers said, and neurological symptoms usually occurred along with respiratory symptoms. 

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The study, funded by the National Institute of Environmental Health Sciences, showed people with a previous history of migraine or chronic fatigue syndrome are more likely to have symptoms equated with neurotoxic shellfish poisoning, which can be caused by eating red tide-contaminated shellfish. Effects include nausea, vomiting, diarrhea, numbness and tingling, dizziness, headache and the switched temperature sensations. This study showed that such symptoms can appear even if people haven't consumed tainted shellfish.

Abdullah said the scientists hadn't expected the poisoning-like symptoms. Another discovery: "Repeated airborne exposures in otherwise healthy people can also make them more sensitive to red tide."

A 'good first step'

Calling it a "good first step," she and co-author Barbara Kirkpatrick, Gulf of Mexico Coastal Ocean Observing System senior advisor, acknowledged that the study raises many more questions than it answers: Why do different people react differently? How much toxin needs to be present to cause symptoms? Are there potential long-term impacts, as have been shown to occur with some toxins produced by freshwater cyanobacteria, also called blue-green algae?

Until more is known, minimizing exposure is sound practice, Kirkpatrick says. "Use the precautionary principle. If you get a terrible cough every time you go to the beach during a red tide or you get a bad headache, be careful," she said.

A great way to determine risk, Kirkpatrick says, is the Red Tide Respiratory Forecast, an online tool to help people see which beaches could have red tide impacts throughout the day and what the best time to visit a particular beach will be. "People can know what's going on out there and make good decisions," she said. "We're all supposed to do that as adults anyway."

She also points out that the scientists doing this work aren't in some distant ivory tower. "We live in this community," Kirkpatrick said. "We care about what the health impacts are, so we're going to be pretty relentless."

Learn more

For more information about this red tide clinical research study at the Roskamp Institute, please call: 941-256-8019, ext 3046.