On August 12, 2014, a man arrived at a hospital in Anchorage, Alaska, with peculiar symptoms and an even stranger story. He was suffering from fever, cough, nausea, pain, and a bitter metallic taste in his mouth, but he already had an idea of who the culprit might be, and it was a doozy: a zoanthid coral.

There are few places that seem less likely for a zoanthid coral attack than Anchorage, Alaska. And yet such a coral managed to poison around a dozen people and animals in their homes and places of work in Anchorage over the last few years, according to a report last month in the CDC's Morbidity and Mortality Weekly from scientists at Alaska's Division of Health and the U.S. Food and Drug Administration.

What attacked the people and animals was not the corals per se, but a substance called palytoxin. This molecule binds to the sodium-potassium ATPase, a protein crucial to normal cell functioning that uses the fuel ATP to pump sodium ions out of cells and potassium ions in.

The resulting chemical gradient (lots of sodium outside wanting to get in, lots of potassium inside wanting to get out, per the rules of diffusion) powers many other important cellular functions, among them importing food and nutrients into the cell. Palytoxin silences the pump, destroying the ion gradient and killing the cell. In large enough doses, entire animals and humans die too. But how does this toxin get into people?

Zoanthid corals are popular aquarium denizens often recommended to newbie aquarists because they are attractive and are considered easy to grow.

"Zoanthus-dragon-eye" by Kazvorpal - Own work. Licensed under CC BY-SA 3.0 via Commons.

Most aquarium hobbyists have assumed that you must touch the coral in order to be poisoned. That contact can occur because the corals, like many garden plants, must be thinned from time to time, and it is not an easy task. They cling tightly to the rocks on which they live. Removing them involves cutting, scraping, attacking with chemicals, or even scalding with hot water. Physical contact with the coral while engaging in these destructive methods is an obvious means by which toxin and human may meet.

But evidence is growing that there may be more insidious routes of exposure, and the Anchorage cases seem to support this.

The man who showed up in the ER on August 12 had not worked with or handled a zoanthid coral. But one of his relatives had. Just 7-8 hours earlier, this relative had transferred 70 pounds of live zoanthid coral from a plastic container into the patient's 200 gallon aquarium inside his 1,600-square-foot mobile home.

A fuzzy photo of the perpetrator. The coral -- or a part of it -- collected from the 200-gallon home aquarium in the mobile home in Anchorage. Figure from Hamade et al. 2015. Click here for source.

While this was being done, some pieces of the coral fell on the floor, and some live polyps broke off.

Two people were sleeping in a room next door. The man who later showed up in the ER got home later and slept for seven hours in the same room as the aquarium.

All through the night -- and let me emphasize that you just can't make this stuff up -- the coral seems to have exuded some sort of creeping death mist. According to the CDC's venerable Morbidity and Mortality Weekly, “Patients A and C noted a visible mist and sensed humidity in the mobile home on the morning after coral introduction, leading them to suspect a possible problem with the aquarium.”


The other two people recovered on their own by about 7 pm the day of the poisoning. A dog and cat in the same mobile home appeared “lethargic” the day of the hospitalization, the patients, said, and the dog had also vomited the morning after the coral arrived. Yet none of them – people or animals -- had touched or handled the coral. But the person who'd transferred the coral into the aquarium had no apparent symptoms.

The shop owner where the coral was procured also reported numerous previous poisonings among his staff, the most recent of which occurred in July 2014 during the disassembly of a customer's aquarium and involved at least five people including himself. All recovered.

The owner also knew of two probable poisonings in 2012. A man cut zoanthid polyps from their rock base under hot water in a garage. During the process, his wife and dog passed through the garage several times. The woman was pregnant. Within hours, husband and wife suffered fever, tremors, and weakness. Their dog vomited and acted lethargic. The pair were hospitalized in the ICU for several days, where the wife spontaneously delivered her baby three months prematurely. The infant survived and apparently suffered no long-term ill effects. However, the husband suffered respiratory problems for at least two years.

Together, these stories strongly imply the toxin can go airborne to sicken people. But that begs another question – how did the toxin get from the water to the air in sufficient concentrations to wreak all this havoc? And if the air was laced with poison, what was the situation in the water for any hapless fish who might have been there? Did they all go belly up? The article does not say.

When samples of coral from the shop and home aquarium were analyzed, the scientists found the shop sample contained 6.2 milligrams crude palytoxin per gram of wet weight coral and the home sample contained 7.3 mg/g. Both exceeded values measured in corals previously involved in poisonings of 0.5 mg/g-3.5 mg/g.

DNA analysis of the corals showed that both toxin-containing samples were similar to a species of Palythoa implicated in previous poisonings in Maryland, Virginia, New York, and Ohio. The envenomated corals also looked physically distinct from the nontoxic or weakly toxic specimens sampled in this and previous poisonings, the authors of the MMWR paper said -- but they did not describe how, which seems like it could be useful information.

Some people do appear to be able to maintain their pet Palythoa without poisoning themselves, perhaps because they handle them carefully and decontaminate thoroughly, the scientists wrote in MMWR. Or maybe they are just lucky. No US regulations mandate testing or labeling of potentially toxic corals, nor do they offer any general recommendations on safe coral handling and decontamination procedures.

Though the shop where the corals in the Alaska cases were purchased displayed many warning signs about the potential toxicity of the coral, that did not stop many staff and customers from getting poisoned. Preventing coral poisoning currently seems to be a matter of uneducated guesswork, and it will continue to be until someone uses science to figure out exactly how palytoxin infiltrates the bodies of people who have never even touched them or the water they live in.


Hamade, Ali K., Sandrine E. Deglin, Joe B. McLaughlin, Jonathan R. Deeds, Sara M. Handy, and Ann M. Knolhoff. "Suspected palytoxin inhalation exposures associated with zoanthid corals in aquarium shops and homes-Alaska, 2012-2014." MMWR: Morbidity and mortality weekly report 64, no. 31 (2015): 852-855.