Rising ocean temperatures and coral reef disturbances have not contributed to an increase in the rates of ciguatera fish poisoning in the U.S. Virgin Islands as was previously feared. That is the conclusion of a recent study by research scientists from the University of Florida’s Departments of Epidemiology and Medicine and the University of the Virgin Islands. The findings were published in the May issue of the American Journal of Tropical Medicine and Hygiene.
Similar studies conducted in the South Pacific suggest that increases in water temperatures trigger an increase in the growth of a specific marine alga, Gambierdiscus toxicus, which produces a group of closely related toxins known as ciguatoxins. Ciguatera fish poisoning, also known as CFP, occurs when people eat fish that have accumulated these toxins.
But when researchers – using new telephone survey data and an analysis of emergency room records – compared the recent incidence of CFP in St. Thomas to a similar survey conducted in 1980, they were surprised to find the rate had remained stable or even declined.
The researchers surveyed more than 800 St. Thomas residents at random by telephone during 2010 and 2011. They found that the annual incidence of ciguatera fish poisoning among adults was estimated at 12 per 1,000 residents, compared to 14 per 1,000 residents in 1980. Even more surprising was the drop in emergency room visits for CFP, based on a comparison of medical records. In the 1980 study the rate was 18 per 1,000 residents, while in the most recent study the rate was six per 1,000.
“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,” said Dr. Glenn Morris, a co-author of the study and director of the University of Florida’s Emerging Pathogens Institute. “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.”
UVI’s Dr. Tyler Smith, a research assistant professor of marine science, who participated in the study, called the findings “a great surprise.” "This is one of the first major human studies of ciguatera fish poisoning conducted since the 1980s,” Dr. Smith said. “The results are a hopeful sign. Either the Virgin Islands reefs are not becoming more dangerous for fish consumption or that the providers of local seafood have made the supply safer by closely controlling which fish make it to market.” Either way, Dr. Smith said further research is needed. “It will help us to understand which of these factors are most important."
According to the scientists, when herbivorous reef fish eat seaweed or algae, they consume the Gambierdiscus organisms, and the ciguatoxins build up in the fish’s flesh. Higher levels of toxins are seen in predatory reef fish that feed higher up the food chain. The toxin cannot be removed from fish through either cooking or freezing. Symptoms of CFP include nausea, vomiting and diarrhea followed by several neurological problems such as tingling in the hands, feet and face, and pain and weakness in the lower extremities.
The study was supported by the Centers for Disease Control and Prevention and the National Oceanographic and Atmospheric Administration. Other partners in the project included the Woods Hole Oceanographic Institution, the University of Maryland and the U.S. Food and Drug Administration.