In most cases, swimming into a swarm of extremely venomous jellyfish is very bad luck.

But University of Hawaii researcher Angel Yanagihara’s painful encounter with box jellyfish 16 years ago during a swim off Oahu ultimately led to a journey this week with Diana Nyad during the renowned swimmer’s historic trek across the Florida Strait.

On her fifth attempt, at age 64, Nyad on Monday became the first person to swim from Cuba to Florida without a shark cage for protection.

Yanagihara, who has pioneered research into the venom and treatment of box jellyfish stings, was one of five divers this week who continuously patrolled the waters around Nyad for sharks, jellyfish and other dangerous marine creatures during her 52-hour, 110-mile swim.

It was Yanagihara’s second stint on Nyad’s team of assistants. Nyad selected Yanagihara last year as an adviser for marine hazards after anguishing box jellyfish stings paralyzed parts of her body, slowed her breathing, and ultimately ended an attempt at the record swim in 2011.

"I was on fire. Excruciating, excruciating pain," Nyad recalled of the box jellyfish stings in a 2012 talk for the nonprofit Technology, Entertainment, Design conference series. "First, I feel like boiling hot oil I’ve been dipped in, and I’m yelling fire! fire! fire!" she said. Next came paralysis in her back and chest, and difficulty breathing, Nyad recounted. A fit 29-year emergency medical technician was also stung after he jumped in the water to help her, according to Nyad, and got back onto the boat crying in agony.

It’s a feeling Yanagihara never forgot. Her 1997 swim into Hawaiian box jellyfish off Kaimana Beach in Waikiki, weeks before she wrapped up a doctorate program at UH, led her to investigate why the stings were so painful — and what scientists knew about one of the most venomous creatures on the planet.

"After I got stung, I got really motivated by my own questions," Yanagihara, an assistant research professor affiliated with UH-Manoa’s Pacific Biosciences Research Center and the Department of Tropical Medicine, said Tuesday.

At the time of her sting, Yanagihara discovered there was still much to learn about the potentially lethal box jellyfish and its venom. Through her research at UH-Manoa, she determined the most active toxic agent in the box jelly venom was similar — but not related — to the toxic protein agent in anthrax. Her research led to a treatment for box jellyfish sting that works to inhibit a toxin in the venom.

This year, Nyad wore on her skin what Yanagihara called a "sting-stopper." Yanagihara described it as a gel-like, "slimy-goo" substance that her venom research helped develop. The substance greatly diminishes a box jellyfish’s capacity to sting, and it also inhibits any venom that does get through, Yanagihara said. Nyad applied the sting-stopper about every hour or so during the swim, Yanagihara said. It was the second year in a row that Nyad used it.

Nyad also wore a special mask to protect her face from box jellyfish. However, the mask proved to be too tight — making it difficult to breathe — so Nyad didn’t use it after the first night, Yanagihara said.

Yanagihara said she was on standby all summer while Nyad and her crew waited for the right conditions to emerge in the Florida Strait. Nyad’s team put her on alert early last week, and Yanagihara then left Wednesday and arrived in Havana at about midnight Thursday.

The trip across the strait was grueling for Yanagihara, too. The UH researcher said she got only three hours of sleep during Nyad’s 52-hour swim, and that she dove into the water every 15 to 45 minutes to check not only for jellyfish, but also sharks. Two other divers who had been assigned to shark duty couldn’t make the trip, Yanagihara said. Nyad’s team paid for Yanagihara’s travel but she wasn’t paid beyond that, she said. She participated in the record-breaking swim out of admiration for Nyad.

"I felt that she was a heroic individual with a great vision, and her love of the ocean is something that I relate to pretty strongly," Yanagihara in a phone interview from Florida on Tuesday, as Nyad and other members of the team celebrated the historic swim in the background. "On multiple levels I felt it was an important thing to try to assist."

Nyad and her team encountered many jellyfish during the swim — but there were no stings, Yanagihara added.