Algal toxins accumulate in fish and cause poisoning in people

Flickr/USFWS Pacific

[FIJI] Rising sea temperatures caused by climate change may have contributed to a sharp increase in the incidence of a severe form of tropical fish poisoning afflicting people living on small islands around the Pacific region, a study has shown.

A 60 per cent increase in the annual number of ciguatera poisoning cases in 18 Pacific island countries and territories between 1998–2008, compared with the period 1973–1983, was among the findings in the study, which was published last month in PLoS Neglected Tropical Diseases (13 December).

Up to a quarter of the region's population may suffer from the poisoning during their lifetime, the researchers estimate. The incidence was highest in Tokelau, Cook Islands and Marshall Islands.

Ciguatera is caused by toxins produced by Gambierdiscus spp. algae which accumulate in certain species of reef-feeding fish. The researchers suspect that higher sea temperatures that cause algal blooms, along with damage to coral reefs caused by cyclones, are to blame for the increases in ciguatera afflictions.

Although people may not die from the poisoning, it is still serious enough to cause severe gastrointestinal problems, as well as neurological effects that can incapacitate sufferers for weeks or even months.

 "We need a much better understanding of the ecosystems that produce and accumulate the ciguatera toxins, and the environmental factors that affect them," said Richard Lewis, a molecular pharmacologist at the University of Queensland's Institute for Molecular Bioscience in Australia, and one of the authors of the study.

"The fear is that, with global warming and continued reef degradation, ciguatera poisoning will continue to rise unless we develop effective management practices."

The study called for better diagnostics and treatments. At present, the toxin can only be detected in fish and algae in specialized labs. Diagnosis of poisoning is based only on symptoms and recent consumption of potentially poisonous fish, and is therefore not very reliable.

There is no known cure, and treatment is aimed at alleviating symptoms, although researchers are working on developing an antidote based on a traditional medicine.  

Other than the impacts on individual health and livelihoods, ciguatera could have a range of unacknowledged social and economic impacts as well. Non-communicable diseases, such as diabetes and obesity, which are largely due to poor diet, are one of the region's biggest health problems.

The risk of ciguatera poisoning risk may be adding to this, as people turn away from what was formerly an important part of their traditional and healthy diet.

"Ciguatera is the region's most important food contamination problem," said William Aalbersberg, director of the Institute of Applied Science at the University of the South Pacific. "It needs much more attention from the research community than it is currently getting."

Link to full paper in PLoS Neglected Tropical Diseases  [158kB]