Ciguatera Fish Poisoning: Science and Policy

The Science of Ciguatera: Cause
Ciguatera Fish Poisoning (CFP) is caused by toxins produced by dinoflagellates of the genus Gambierdiscus.[1] Dinoflagellates are a large group of single-celled marine plankton, many species of which are photosynthetic. At present, 11 different species of Gambierdiscus are known to produce over 40 different Ciguatera-inducing toxins.[2] Gambierdiscus species require specific environmental conditions to grow: annual water temperatures between 25-29ºC,[3] availability of aquatic plants on which to grow,[4] low water turbulence, and shallow waters.[5] These conditions are readily present in French Polynesia, especially in lagoons and along the leeward sides of islands, where the presence of coral reefs allow macrophytes – such as the seaweed genus Jania and the algae genera Amphiroa and Halimeda – to flourish, providing the necessary substrate for Gambierdiscus growth.[6]

Gambierdiscus growth is not harmful to humans unless a high concentration of toxin-producing cells (>1000 cells/gram seawater) develops, called a bloom.[7] The conditions required for a bloom are not well understood, but include extended periods of elevated sea surface temperatures (SSTs) and high nutrient levels, both of which are found in French Polynesia. Proximity to the equator provides year-round elevated SST with seasonal temperature spikes, while island runoff and upwelling of nutrient-rich ocean water around the islands’ steep slopes provide substantive nutrient supply.[8] Gambierdiscus cells produce ciguatoxin, which can accumulate in the tissues of edible fish when produced at bloom concentrations. The conditions for toxin production in Gambierdiscus appears to be dependent on various factors, such as light, and Gambierdiscus growth stage and genetics.[9],[10] Herbivorous fish are at highest contamination risk in French Polynesia, since their diet consists largely of the macroalgae and seaweed that Gambierdiscus spp. grow on.[11] Since each island in French Polynesia has its own set of environmental conditions and macrophyte species, different reef fish species are affected in different regions. On Rangiroa atoll, Napoleon fish, parrotfish and unicorn fish are always considered unsafe to eat, while the Balistre fish is considered safe when the scales are yellow but unsafe when black.[12] Indeed, the Napoleon fish (Figure 1) and the parrotfish (Figure 2) appear to consistently contain Ciguatera toxins across the nation.[13] The human disease CFP occurs when people consume fish tissue containing elevated levels of ciguatoxin. The Louis Malarde Institute (ILM), a public health research institute based in Pape’ete, records over 500 declared cases of CFP per year in French Polynesia, though they estimate the actual number is closer to 2000 per year.[14] The ILM believes this disparity is a result of the fact that western medicine has no treatment for CFP, so afflicted individuals do not report to a local clinic or hospital, which are the ILM’s source for poisoning data.[15]

Figure 1. The Louis Malarde Institute has found that Napoleon fish are frequently contaminated with ciguatoxins across much of French Polynesia.[13] Photo credit: R.F. Myers.[41]

Figure 2. The parrotfish is another reef fish identified by the Louis Malarde Institute as commonly contaminated with ciguatoxins.[13]Photo credit: R.F. Myers.[42]

Ciguatera toxin becomes a threat to human health as a result of bioaccumulation. The toxin cannot be broken down by the digestive processes of the reef fish that inadvertently consume it with their food sources, and it therefore accumulates in their tissues.[16] Thus, herbivorous reef-dwelling fish popular among island fishermen in French Polynesia are affected, as are the carnivorous fish of the next trophic level. A human diet heavy in fish results in a high risk of exposure to tissue containing high toxin concentrations. Ciguatera toxin is very heat-stable, meaning that standard cooking temperatures used to prepare fish for human consumption do not remove the toxin.[17]

The Science of Ciguatera: Medical
CFP victims display a wide variety of symptoms including gastrointestinal, neurologic, and cardiac symptoms (Figure 3). The onset of symptoms is rapid, from 30 minutes to 24 hours after consumption.[18] Gastrointestinal symptoms, such as vomiting and diarrhea, often occur in the first 48 hours, while neurological symptoms–which develop later and can last for weeks or months after the initial exposure–include tingling, trouble with cold perception, headache, dental pain, metallic taste, vertigo, lack of coordination, itching, and hypersalivation.[19] Cardiac symptoms, such as bradycardia (slow heart rate) among others, have also been reported in some individuals within the first three days of exposure and appear to be an indicator of a more severe infection.[20] Fever, respiratory distress, and chills may be present, though all patients exhibit a different suite of conditions. One study noted that victims who consumed fish organs, such as the liver or brain, were more likely to develop severe Ciguatera symptoms than those who simply ate the fillet.[21] Ciguatera has a low mortality rate (<1% in the Pacific),[22],[23] though symptom duration can last years.[24] Because no treatment for the toxin exists, patient care for CFP is largely done on a case-by-case basis, treating symptoms as they arise.[25],[26]

Figure 3. The most common symptoms associated with Ciguatera Fish Poisoning and their durations.[19],[20]

The Science of Ciguatera: Effects of Climate Change
Any natural and man-made disturbances to coral reefs can increase the presence of Ciguatera-producing Gambierdiscus species. Coral reef destruction from bleaching, dredging, blasting, military explosive testing, and hurricanes have been directly linked to CFP outbreaks.[27],[28] These disturbances kill coral, generating brand new substrate upon which macroalgae grow and consequently providing new habitat for Gambierdiscus populations to bloom on.[29] Further, the presence of human pollutants and sewage waste provides nutrients to macroalgae species further fueling the growth increase in Gambierdiscus species.[30],[31]

Another main concern about CFP is the potential influence of climate change on the geographic range of the disease. It is feared that as the Earth’s climate warms, changing conditions could favor blooms of toxic dinoflagellates in a larger portion of the Earth’s oceans.[32] The ILM has already observed the geographic expansion of Ciguatera in French Polynesia. Before 2009, no cases of CFP had been reported on Rapa Island, which, located at 27ºS, is one of the southernmost islands in the country. However, during 2009, more than 50% of the population were affected.[33] This account provides evidence of the extension of Gambierdiscus spp. range farther into the Southern Hemisphere than previously recorded, suggesting that as SSTs rise, the geographic range of Ciguatera is increasing. Further, in 2005, Chateau-Degat et al. created a model that compared SST data and reported CFP cases during the years 1993-1999, attempting to determine a relationship between the two variables and make future predictions about Ciguatera proliferation.[34] They examined data from the Atimaono barrier reef in the Papara district of Tahiti and found a statistically significant, direct relationship between SST and the densities of Gambierdiscus spp. They also noted that a higher density of the ciguatoxin-producing dinoflagellates lead to more reported cases of CFP.[35]

In 2010, however, another study examined the same relationship through a regional analysis of Ciguatera in the southern Pacific Ocean.[36] Toxic dinoflagellates displayed effective blooms only within a certain SST range (24-30ºC) and Ciguatera was not nearly as prevalent at SSTs below or above that range.[37] Rising global temperatures may therefore not have the adverse effects that have been hypothesized, should rising SSTs result in reduced prevalence of Gambierdiscus blooms.[38]

Ciguatera is the most commonly reported marine toxin disease in the world and is endemic to French Polynesia.[39],[40] The disease, while rarely lethal, can result in devastating, long-term symptoms in victims and should therefore be addressed as a major public health concern in Tahiti, considering the endemic nature of Ciguatera and fish-heavy diet there. And with SSTs rising, Ciguatera is likely to remain a dominant public health problem in the region. Certain French Polynesian organizations have acknowledged the risk of CFP and have begun to address the epidemiological factors that make it locally prevalent. Below, we examine policies influencing how Ciguatera is being approached and suggest future actions for the region.

Policy and Management of Ciguatera
Tahiti is renowned for its stunning volcanic mountains, black sand beaches, and beautiful fringing reefs. It is a popular vacation destination for French and American tourists and yet it hides an elusive, incurable, seafood-borne disease: Ciguatera. Residents and vacationers alike can find themselves experiencing intestinal pain, lack of coordination, and headaches within hours of consuming a meal of local fish. But unlike normal food poisoning, Ciguatera Fish Poisoning (CFP) symptoms can last for extended periods of time,[43] and become crippling and chronic. The implications of CFP on human populations are varied and significant; in south Pacific island communities, where much of the economic, social, and political activity is based around the ocean, impacts can be huge. A study on Raivavae Island in French Polynesia identified five major impacts of Ciguatera on the island’s society: fish is ruined as a major food source; fishing industries face economic loss; tourism industries lose revenue; the cost of maintaining public health rises; and monitoring and management costs rise.[44] The combination of these losses makes Ciguatera a pressing issue for French Polynesia.

Chinain et al. examined the risk management strategies employed on Raivavae Island, an island in French Polynesia roughly 450 miles south of Tahiti. They found that local fishermen could accurately identify species of fish contaminated by the toxin, when survey results from fishermen were compared to antibody testing of fish tissue. They also found that locals could accurately determine the locations on the island from which it was unsafe to eat fish.[45] Indeed, during an interview in Nuku Hiva, local residents could point to such regions of the islands when asked about Ciguatera.[46] These findings suggest that the use of local knowledge in policy decisions may be an effective method of monitoring CFP outbreaks and help break the persistence of the disease in Tahitian communities. Chinain et al. also took part in a community outreach program, which advised individuals to avoid particular species of fish and fishing areas and stressed the importance of reporting cases of Ciguatera.[47] In the Raivavae study, this information appeared to create a self-regulating behavior among individuals and may have helped reduce poisonings.[48] The researchers also found, however, that CFP is grossly underreported on Raivavae,[49] and indeed, this apparently is the case throughout much of French Polynesia.[50] This may be due to several causes, including disinterest in reporting cases by medical officers, and individuals seeking official medical treatment for only the most severe cases.[51]

Researchers from one French Polynesian public health organization, the Pape’ete-based Institute Louis Malarde (ILM), have tried to obtain better epidemiological data on Ciguatera in order to improve community responses (Figure 4). They have utilized CFP reporting forms (Figure 5), which are distributed to clinics across French Polynesia, to try to gather information about the temporal and spatial trends in Ciguatera poisoning within the country.[52] The ILM also completes field studies throughout French Polynesia, aiming to gain a better understanding of the disease. These research projects involve meetings with local leaders, as well as outreach programs to educate local fishermen about the disease. Informational posters, written in French and Tahitian, are also distributed to local health centers (Figure 6). The researchers also sample local algae, microalgae, and fish; these samples are processed to determine their toxicity.  Through samples like these, the ILM continues to obtain information about Ciguatera, increasing their understanding of the disease.[53]

Figure 4.  The Institute Louis Malarde, based in Pape’ete, Tahiti, French Polynesia. Photo by the authors.

Figure 5.  Ciguatera health survey for the island of Tahiti, distributed by the Institute Louis Malarde (ILM).[10]

Figure 6.  A Ciguatera informational poster, written in Tahitian, that is distributed to local health centers by the Institute Louis Malarde. Photo by the authors.

ILM researchers have also examined local treatments of Ciguatera.  In French Polynesia, residents use tests to attempt to predict the presence of the disease in a fish; some will leave a piece of the fish out in the open and observe if it attracts flies or ants, while others will feed the fish to their cat or dog.  Based on studies by the ILM, these tests have not been shown to be significantly effective.[54] The French Polynesian islands also boast a wide variety of local treatments of Ciguatera.  While the ILM has reported that most of these focus primarily on individual symptoms, a local tree, known as Fauxtabac or Tohonu (Figure 7), has shown some promise in treating Ciguatera as a whole.  The leaves from this tree, when consumed as a tea within the first 24 to 48 hours of the disease, appear to interact with the toxin and limit the its impact on the nervous system.[55] Other studies have identified various traditional remedies that are helpful in treating symptoms, though they are not necessarily effective in interacting with the disease itself.[56] Even modern medicine only targets symptoms, as no cure is yet available for the disease.[57]

Figure 7.  One local treatment, taken from the tree known as Fauxtabac or Tohono, has shown some promise in counteracting the toxin that causes Ciguatera.[8] Photo by the authors.

At a 2008 conference on Ciguatera and related biotoxins held in New Caledonia, 71 international experts and representatives from 21 countries came together “to establish and/or strengthen the partnership between the scientific teams and between scientists and managers on focal island countries, including the Pacific, where the incidence of CFP is strong.”[58] The conference highlighted the need for management of Ciguatera risk, detection systems for Ciguatera toxins, and the creation of a website devoted to practices to standardize the techniques of research and management of Ciguatera risk–including protocols to implement during an outbreak of Ciguatera, videos for staff training, photos to recognize the species of dinoflagellates in the field, and alert messages.[59] To help standardize the French Polynesian laboratories studying Ciguatera, the US Food and Drug Administration (FDA) has expressed interest in working with the ILM for the establishment of laboratory technique and methods standards for Ciguatera toxin detection.[60]

To prevent the spread of CFP, both residents and tourists should be aware of the types of reef fish that are likely to be contaminated. Educating fishermen, the resident public and the tourist industry about the species of fish that are relatively safe to eat could help prevent outbreaks of the disease. Visits to the islands of Tahiti, Rangiroa, and Nuku Hiva have shown that very little information is currently available for tourists traveling there; this is likely consistent throughout French Polynesia.

Educating residents about the origin of the disease could also produce benefits for communities; the ILM reports that many residents French nuclear tests to have created the disease, a false assumption.[61] This belief may have a factual basis, however, as military operations, as well as other activities that disturb coral reefs, can lead to the proliferation of Ciguatera.[62] Further, the public should also be aware of the sizes of fish most likely to carry the disease; the United States government recommends avoiding fish over 3 kg or 6.6 lbs.[63] Similarly, individuals should avoid consuming the head, roe and viscera of potentially toxic fish, as the toxin accumulates at higher concentrations in those organs.[64] Recently, the sexual transmission of Ciguatera between two adult humans has been observed; this adds safe sex practices to prevention methods that should be taught to the general public.[65]

As can be seen above, education plays a prominent role in Ciguatera policy. In 1991, the Fisheries Information Project, a branch of the South Pacific Commission (now the Secretariat of the Pacific Community, SPC), attempted to raise Ciguatera awareness by creating the SPC Ciguatera Bulletin (Figure 8), an informative document that circulated throughout the Pacific region.[66] These bulletins outlined dangers involved with CFP, and were designed to provide a foundation for the discussion of preventative measures being taken throughout the region.  Each release of the annual bulletin also presented information about research being completed on the disease.  Unfortunately, new information could not be collected on a timely basis, and the program was discontinued after the release of the third bulletin in 1993.[67]

Figure 8.  The heading for the SPC Ciguatera Bulletin, distributed from 1991-1993 by the South Pacific Commission (now known as the Secretariat of the Pacific Community).[24],[25]

Though French Polynesia has begun to develop policies for mitigating the effects of CFP, their response to the disease is still quite limited. Even across the globe, few effective policies exist for identifying and treating Ciguatera. In the United States, Florida has listed Ciguatera as a reportable disease, meaning that all health professionals (even veterinarians) are required to report any cases of Ciguatera to local health officials, like the Florida Department of Health. Florida’s Food and Waterborne Disease Surveillance Program also works to combat the disease, and their website offers public information about symptoms and advice to seek medical attention if symptoms manifest.[68]

When a person is diagnosed with Ciguatera poisoning, samples of the ingested fish along with blood and urine samples from the patient, are sent to the U.S. Food and Drug Administration where researchers investigate the toxin, attempting to find a biomarker in humans; this could lead to a more effective diagnosis of the disease in people.  Community outreach programs are also being implemented across the United States, aiming to educate the general public about Ciguatera.  Since CFP is under-reported and under-diagnosed in general, the hope is to increase awareness about the disease, possibly leading to a greater understanding of how to treat and prevent it.[69] Scientific papers on the subject have called for more outreach programs, and have asked lawmakers to post signs for fishermen, indicating which reefs are typically associated with the disease.[70]

Further research has also led to the development of some self-check tests for fishermen, mainly the Cigua-Check™ system in Hawaii. Available for US$20, this field test can be used by fishermen to determine whether a catch carries ciguatoxin. In 2001, the Cigua-Check™ was tested on 176 fish samples known to be carrying the ciguatoxin. The test, which can result in positive, borderline, or negative readings, resulted in a 92.3% accuracy of correct readings of the samples.[71] That being said, this test was later determined to be slightly more difficult to read than initially thought. In 2011, Bienfang et al. recruited four different test subjects to use Cigua-Check™ to examine known fish samples and deliver a verdict on their toxicity. Based on the results of the study, the users rarely agreed, probably indicating that the method may not yet be ready to distribute on the open market.[72]

Ciguatera is commonly found in and therefore presents a significant challenge to policy makers and scientists across the equatorial Pacific region. Though the disease has been documented since the 1700s,[73] a cure has yet to be found, and effective management of the disease still vexes policymakers. In future years, more study is recommended, hopefully leading to a greater understanding of the disease and its limiting factors. Results from these studies could inform policymakers of appropriate responses to the disease, potentially marking the end of its effects on human lifestyles.

Sam Eley, Bowdoin College
Drew Gustafson, Bowdoin College


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How to cite this page:
Sam Eley and Drew Gustafson. 2014. “Ciguatera Fish Poisoning: Science and Policy.” Atlas for Sustainability in Polynesian Island Cultures and Ecosystems. Sea Education Association, Woods Hole, MA. Web. [Date accessed]  <html>