Fewer people getting ciguatera

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ST. THOMAS - The results of a study on ciguatera fish poisoning were published in the May issue of the American Journal of Tropical Medicine and Hygiene.

Contrary to what researchers initially suspected, the multi-year, collaborative research project found no conclusive link between warmer ocean temperatures and the number of people getting sick.

The public health part of the study, which mirrored a study done in the 1980s, found that rates of ciguatera poisoning in the local population have decreased in the last 20 years.

However, the study's initial findings do not mean a connection between warmer seas and ciguatera does not exist.

Other factors that could be contributing to lower rates of fish poisoning in the territory include greater public awareness of ciguatera, fishermen avoiding areas with poisoned fish and fewer people eating locally caught fish, according to University of the Virgin Islands coral ceef researcher Tyler Smith.

The ciguatera project began in December 2009 as a joint venture between the University of Florida, UVI, the University of Maryland School of Medicine, Woods Hole Oceanographic Institution, Schneider Hospital, the Food and Drug Administration Dauphin Island Lab and Florida State University.

The project's purpose was to study how ciguatera works its way up the food chain, how it affects human health and whether climate change or environmental factors contribute to higher or lower instances of poisoned fish.

Ciguatera poisoning is caused by naturally occurring toxins, called ciguatoxins, that are produced by microscopic plants - gambierdiscus toxicus - that live on seaweed and other surfaces within coral reef communities. When fish eat seaweed or algae, they also consume the organisms and the ciguatoxins build up in the fish's flesh.

The toxin is fat soluble - it is stored in the fish's body and not excreted - so it builds up as it goes up the food chain. The bigger fish eat the little fish, and the toxin gets passed on until it is consumed by humans.

Predators at the top of the food chain - such as barracuda - can end up with large amounts of the toxin in their flesh. No test can be done to determine whether a fish is poisoned, and cooking and preparation methods have no affect on the toxin.

The public health part of the study is completed, and the results have been published.

The work was led by Dr. Glenn Morris, principal investigator and director of the Emerging Pathogens Institute at the University of Florida.

Morris did work in the territory in 1980 to study ciguatera, and his results from that research were compared with the new data collected in 2010 and 2011.

In 1980, about seven per 1,000 residents had been affected by fish poisoning, and about 22 percent of households reported being affected by ciguatera in the prior five-year period, according to the study.

About 800 people participated in the recent telephone survey, which found that about 23 percent of those surveyed had experienced ciguatera at some point in their lives.

The telephone survey showed that about 12 people per 1,000 have been affected by the poisoning.

By looking at emergency room records at Schneider Hospital, the researchers calculated an incidence rate of about six per 1,000, compared with about 18 per 1,000 in the 1970s.

"While ciguatera fish poisoning has been recognized as an important public health problem in the Virgin Islands for many years, we still have very little understanding of the factors that increase the risk of toxicity," Morris said. "It is important that we understand the potential impact of climate change and rising sea surface temperatures on the occurrence of this disease. It is possible that changes in fish consumption in the Virgin Islands population have masked the effect of climate change, but we don't yet have enough data to know for sure."

Smith, who is leading the environmental side of the study looking at the amount of ciguatera found on the reefs and in the reef fish, said either the territory's reefs are not as dangerous for fish consumption or that the providers of local seafood have made the supply safer by controlling which fish make it to market.

"Is it because the reef hasn't changed in toxicity, or is it that the reef has changed, but human behavior has also changed," Smith said.

Either way, more research is needed, he said.

While the public health side of the study is completed, Smith and stateside research partners are continuing to look at the ciguatera found on the reef. With funding from a harmful algae bloom research grant from the National Oceanic and Atmospheric Administration, the collection and testing of samples from local reefs will continue for four years.

"There will be more coming out periodically on different aspects of the project," Smith said.

For more information about the ciguatera research project, visit www.caribcatch.org.

- Contact Aldeth Lewin at 714-9111 or email alewin@dailynews.vi.

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