A regular Source feature, Undercurrents explores issues, ideas and events as they develop beneath the surface in the Virgin Islands community.
If you’ve ever met a little guy called Gamberdiscus, genus dinoflagellates, you aren’t likely to forget the encounter.
The marine micro-algae likes Caribbean waters. It grows here on reefs where it produces a group of related poisons known as ciguatoxins.
Eaten by small herbivorous fish, the dinoflagellate works its way up the food chain, its poisonous nature hidden and completely undetected, passing into larger carnivorous fish and, if luck will have it, onto a human’s dinner plate.
Next stop may be the emergency room.
Or, as is becoming more and more likely, a scientific lab.
With what is believed to be one of the highest rates of ciguatera fish poisoning in the world, the Virgin Islands is an ideal place to study this disease which has plagued island and coastal peoples for centuries. A team from the University of the Virgin Islands, working with local and national partners, has been diligently researching it for several years.
“It’s really a complex puzzle,” said Tyler Smith, Ph.D., professor of marine science at UVI and the principal investigator for the project for the Virgin Islands.
From a health standpoint, it’s a puzzle worth solving.
As too many residents know, early symptoms of ciguatera can include nausea, vomiting, diarrhea and abdominal pain. Often it stops there.
However, in some cases, victims also may develop a range of neurologic symptoms that can include dental pain, an abnormal tingling or prickling sensation in the extremities or tongue, severe itching, a metallic taste, a reversal of reaction to temperatures so hot feels cold and cold feels hot, weakness, and in more severe cases, respiratory paralysis and coma. Only in rare cases is it fatal.
Symptoms may persist for a day or so, or for weeks or even months. A person who has once had ciguatera poisoning is more susceptible to it if exposed again; in fact, there is some evidence that symptoms can even be triggered by eating fish that is not contaminated.
Researchers have debunked a number of folk myths describing ways of detecting the presence of the toxin. To date, they say, there is no sure way to know whether a fish is infected, short of a laboratory anyalsis.
But marine scientists and fishermen do know a lot about the types of fish most likely to carry the toxin and the areas where it is most prevalent.
“Barracuda’s the most toxic fish that we know of,” Smith said.
Others high on the list, according to David Olsen of the St. Thomas Fishing Association, are horse-eyed jack and schoolmaster snapper.
“You won’t see those at the market,” he said. Fishermen simply won’t offer anything that has as much as a 20 percent chance of carrying the toxin. “One of the biggest safety factors (for a consumer) is to have a relationship with a fisherman because he doesn’t want to poison you.”
A seasoned fisherman also knows to avoid areas where infected fish are prevalent, Olsen said. On St. Thomas, “almost any fish from the north is safe.”
Traditionally, more cases are reported on St. Thomas than on St. Croix, Smith said. Recent research has focused on St. Thomas and its surrounding waters and reefs.
The first major study was conducted in the early 1980s, Smith said. His own research at UVI, supported by the work of graduate students, has been ongoing since about 2009. One study, conducted in conjunction with other institutions, was published in May of this year.
“We’re trying to tackle the major questions,” he said. First of all, is the incidence of ciguatera changing? If so, why? And what are the environmental factors that affect the dinoflagellate carrying the toxin?
To answer the first question, UVI partnered with researchers from the University of Florida and other stateside institutions in a project funded primarily by the U.S. Centers for Disease Control and Prevention and by the National Oceanographic and Atmospheric Administration.
Their focus was not so much the organism itself, but rather the humans affected by it.
They conducted a random telephone survey via cell and landlines of St. Thomas residents, and surveyed 807 people over a two-year period in 2010 and 2011. About 23 percent of the participants, or 186 of them, reported having had at least one episode of ciguatera fish poisoning. And of those 186, 41 percent reported they had more than one episode.
The researchers compared these reports with figures from the 1980 study and found they were roughly equivalent.
They also looked at the emergency room statistics of ciguatera cases from the St. Thomas Hospital (now Roy L. Schneider Hospital) gathered for the 1980 study from 1971-1979, and compared those numbers with more recent ER reports of ciguatera from 1995 to 2011.
The ER records indicated a drop in the numbers over the past 30 years, from an annual mean of 203 cases in the 1980 report covering the 1970s, to an annual mean of 106 in the years between 1995 and 2011.
For those expecting an increase in ciguatera brought on by rising seawater temperatures – as was reported in a similar study in the South Pacific – the results were a surprise.
But researchers are quick to point out that other factors may be in play in the Virgin Islands and could offset the anticipated effects of global warming on the proliferation of Gamberdiscus toxicus and resulting ciguatera.
For one thing, the report showed a significant decrease in local fish consumption.
In the 1980 study, 8 percent of those surveyed said they do not eat fish. In the 2011 study, 17 percent said they don’t eat fish. Further, individual consumption rates have also dropped. Of those who said they eat fish in 1980, 33 percent said they ate it at least three times a week. In 2011, that number had dropped to 12 percent.
There’s also the probability that fewer carriers are making it to market, as both fishermen and their customers are increasingly better educated about fish poisoning.
“Understanding the whole social and ecological phenomenon is important” to understanding the incidence of ciguatera, Smith said. “We’re really interested in that in a future study.”
They are also interested in how environmental factors affect the organism. Is it seasonal? How is it affected by sedimentation? By currents and wave action?
One theory has been that it grows more abundantly on reefs with a high metal content, but Smith said, “there hasn’t been a lot of evidence for that.” However, “there are seasonal changes in reef toxicity,” with warmer periods tending to show more toxicity.
His team of graduate students monitors underwater sites monthly, diving down and checking the alga growth and collecting samples for analysis. On a quarterly basis, they take fish samples.
“We work with the FDA (Food and Drug Administration) and send samples to a lab in Alabama,” he said. There the fish are screened for toxins; those exhibiting ciguatoxins are further analyzed in an attempt to determine concentration levels.
Smith believes that wave action may play an important role in growth of the micro-organism. He points to some circumstantial evidence that ciguatera toxins seem to flourish in more calm waters and he theorizes that rough seas may make it difficult for the culprit to attach itself to reefs. But for now that’s only a guess.
He’s hoping to be able to continue and to expand his studies in collaboration with other researchers in order eventually to solve that and the scores of other parts of the puzzle.
Co-authors on the 2011 study, which appeared in the May issue of American Journal of Tropical Medicine and Hygiene, were Elizabeth G. Radke, Robert L. Cook, and J. Glenn Morris Jr., from the Department of Epidemiology and Emerging Pathogens Institute at the University of Florida at Gainesville; Lynn M. Grattan, University of Maryland School of Medicine; Donald M. Anderson, Woods Hole Oceanographic Institute in Woods Hole, Maine, and Smith at UVI.
That group along with Daena Erdner, University of Texas at Austin, Michael Parsons, Florida Gulf Coast University, and Ronald Kiene, Dolphin Island Sealab in Alabama, are set to meet in October to discuss the direction of future research, Smith said.
