Trouble in paradise: ciguatera poisoning on the rise in Pacific Island nations

Cases of ciguatera poisoning are on the rise among people living in Pacific Island nations, researchers have found.

Smaller fish that feed on dinoflagellates that grow on or near seaweeds accumulate toxins produced by the dinoflagellates. When these small fish are eaten by larger fish, the toxins move up the food chain, accumulating in higher levels in the larger fish. When humans eat the large fish, the toxins cause acutely painful and debilitating effects in the human nervous system, stomach, gut and heart - ciguatera poisoning. The symptoms can last for months.

Researchers from Australia and the United Kingdom investigating the medical records of Pacific Island countries found that ciguatera fish poisoning could have affected as many as half a million people over the past 35 years, making it a more serious public health issue than previously thought.

Between 1973 and 2008, the researchers found a clear increase in the incidence of ciguatera poisoning. Six nations - Fiji, French Polynesia, Vanuatu, Kiribati, the Cook Islands and Tokelau - reported over 2000 cases per 100,000 people per year. The total number of incidents of ciguatera poisoning amounted to nearly 40,000 cases in the eleven years to 2008.

“It all points to a pretty significant increase, and it makes ciguatera more than just a minor health issue,” said co-author Tom Brewer of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.

“While fatalities may be rare, ciguatera poisoning makes people dreadfully ill, so much so they often cannot earn a living for weeks or even months. So it has big social and economic implications. It also restricts the kinds of seafoods than can be eaten.”

“Furthermore, the numbers indicate that if you live in the Pacific you now have a 25% chance of suffering ciguatera poisoning in your lifetime,” Brewer added.

Seaweeds are replacing coral reefs across the Pacific as corals are stressed by human impacts. The research team suspect that the increase in ciguatera poisoning is linked to coral loss and algae growth, nutrient run-off from the land, overfishing, shipwrecks and the microscopic algae that is distributed in ships’ ballast water.

The biggest contributing factor, however, appears to be sea surface temperatures rising to 28 or 29°C and above - making a strong link between the disease and the high temperatures found in lagoon waters that surround islands, which may be exacerbated by global warming.

“Given changes in global climate patterns, increased degradation of coastal marine environments through coastal development and land run-off, and growing exploitation of coastal marine resources, the incidence of ciguatera cases is predicted to continue to increase in the future,” the researchers warn.

“Ciguatera occurs in up to 400 different fish species - and there is no way of knowing if a particular fish has the poison,” said lead author Mark Skinner from the University of Queensland.

“A detection test was previously developed but has proven unreliable, and any future test would likely be unaffordable to most Pacific Islanders. As to managing the disease itself, the best approach may be to try to keep coral reefs intact, with minimal algae cover and to curb nutrient run-off from the land.”

The article, Ciguatera Fish Poisoning in the Pacific Islands (1998 to 2008), was published in the open-access journal PLoS Neglected Tropical Diseases.