The men had ingested a potent fish toxin, a team of doctors wrote at the time in the journal Clinical Toxicology. And they had passed the poison along to their wives through their sperm, the doctors hypothesized. For several weeks, the women had terrible pain and burning in their pelvis.

With fish now imported to U.S. from all over the world, the toxin has since appeared outside its endemic tropical regions — in Vermont, North Carolina and New York. Some researchers are now worrying that warming seas could make the poison even more common.

The toxin, called ciguatera, is one of the most potent poisons on Earth. The molecule pokes little holes in nerves, triggering crazy symptoms: reversal of how you experience temperature, vertigo and the sensation that your teeth are falling out.

"Patients find the symptoms of ciguatera so strange," says neuropsychologist Melissa Friedman, who treats patients for the toxin at Mount Sinai Medical Center in Miami. "I have heard people say they wake up and step on a cold floor and have a burning or uncomfortable sensation."

And then there's dyspareunia, otherwise known as painful sex.

This symptom isn't as common as others, because "it's information people don't normally volunteer to their doctors," Friedman tells The Salt.

But since the two men in the Bahamas first reported a link between dyspareunia and ciguatera in 1989, a few others have also had the unfortunate symptom. For instance, six of nine people who got the fish poisoning from eating amberjack in North Carolina in 2007 complained of painful intercourse, the Centers for Disease Control and Prevention reported. (The Bahamas cases, so far, have been the only ones in which sexual transmission was suspected.)

The toxin can also cause hallucinations or "giddiness," Friedman says, if the fish came from the Pacific or Indian Oceans.

Although ciguatera is new to most people, poisonings are fairly common in tropical and subtropical regions, Friedman says. "In South Florida, ciguatera is considered endemic. It's not foreign to our emergency rooms here." (The CDC says it gets reports of about 30 cases of of poisoning by marine toxins, including ciguatera, each year in the U.S.)

Ciguatera is produced by a single-celled protozoan that sticks to algae on tropical reefs. It then moves up the food chain and eventually accumulates in large, predator fish, such as red snapper, grouper, amberjack and barracuda — species that also happen to be quite tasty.

There's no cure for the poisoning, and treatments only offer minimum relief. Just a few bites from an infected filet, and you may be stuck with the strange neurological problems — and a restrained sex life — for a few weeks, Friedman says.

So what can you do avoid this nasty toxin?

Don't order the red snapper or grouper in tropical places where outbreaks have occurred, she recommends. "You can't detect the toxin by smell or sight. So you really don't know when you're eating it."

Plus, you can't cook, clean or freeze the toxin away from the fish. "That's what so frustrating about the illness," she says. "It doesn't occur because of improper cooking, storing or fish handling."

And when you do eat fin fish that hang around coral reefs, Friedman says, go for the smaller ones, less than about 6 pounds. Or eat a limited portion.

"If you think you have ciguatera fish poisoning, try to save a piece of the fish," she adds. "Then you can send it into the Food and Drug Administration for testing."

At least then you might have a better chance of finding out if your dinner is to blame for an unwelcome interruption of your sex life.

Copyright 2014 NPR.

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