Contaminated fish: food poisoning is increasing in the Caribbean basin

The ciguateraalso called “itching”, is non-bacterial food poisoning the most more widespread worldwide. It occurs as a result of the consumption of marine organisms (Pisces and invertebrates) contaminated with microalgae toxins (algae microscopic) belonging to the genus Gambierdiscus.

Ciguatera and microalgae

These microalgae are dinoflagellates (group of microalgae) benthicwhich need a support to develop (rocks, algae, ropes, plastics…).

This is usually as a result of environmental disturbances from Coral reefs having lost their ability to resilience (as in cases of bleaching) that settle macrophytes (macroscopic algae or higher aquatic plants) conducive to the development of epiphytic dinoflagellates (living attached to plants) such as Gambierdiscus. These dinoflagellates can also proliferate on substrates inert materials of anthropogenic origin (ropes, submerged plastics).

Previously restricted to tropical regions, therange of Gambierdiscus has been extending since the 2000s towards subtropical and temperate regions. the climate change Overall, the lack of treatment of ballast water and the degradation of the marine environment are all conditions at the origin of the health, socio-economic and ecological problems linked to episodes of ciguatera.

To date, the gender Gambierdiscus includes 18 species formally described, which possess morphological and genetic distinct, and exhibit different toxicities and toxin profiles.

Currently, compounds identifiable as ciguatoxins (toxins involved in the syndrome of ciguatera) have only been found in the Pacific, particularly in G. polynesiensis. These toxins become problematic when they are integrated into the food web. Through the process of biomagnification, the concentration of ciguatoxins increases with each trophic level to reach high concentrations in predators higher (as in trevallies and barracudas), making them unfit for consumption.

In addition, bio-transformation phenomena occur and compounds are modified in marine organisms. This makes their study particularly complex, because the compounds present in fish can be very different from those produced by dinoflagellates. Ciguatoxins being thermostable (they are not degraded either during freezing or during cooking), the consumption of contaminated fish exposes the human population to a health risk.

This syndrome rarely fatal would affect each year at least 25,000 people worldwide, an estimate that would represent only 20% of the actual number of cases, given the variability of the symptoms (more than 170 reported) related to this poisoning.

Ciguatera in the West Indies

The Caribbean basin is the second most affected region in the world by ciguatera, after the Pacific Ocean. In the West Indies, it is generally manifested by gastrointestinal symptoms (nausea, vomiting, pains abdominal, diarrhea). They may be accompanied or followed by neurological disorders (itchingburning sensations on contact with cold objects, headaches, fatigue) which are less observed than in other ciguatera foci. Although the most frequently observed cardiovascular symptoms are hypotension and bradycardiathe proportion of the latter varies from one study to another.

Epidemiological studies have shown that the distribution of rates ofimpact of ciguatera is not homogeneous in this region: its prevalence is stronger in the northern islands of the West Indies than those to the south, Martinique being the pivotal zone.

Annual incidence rates between 1996 and 2006 exceeded 15 cases/10,000 population at theepicenter (area of ​​highest prevalence), which extends from Virgin Islands to Montserratwhile the highest annual rate in the low prevalence area was 0.67 cases/10,000 inhabitants between 2012 and 2018 and concerned the Martinique.

In the French West Indies, cases of ciguatera are systematically reported to the Regional Health Agency.

Recently, the annual incidence rate of ciguatera in Guadeloupe increased sharply, reaching 1.43 cases/10,000 inhabitants between 2013 and 2016, which represents an increase of a factor of 5 in 10 years.

This increase could be due to the consumption of new species potential vectors of ciguatera (such as barbarins), which are not on the list of species at risk.

The prohibited species vary from one country and even from one region to another.

Thus, since 2002 there has been a prefectural decree in Guadeloupe framing the sin and the marketing of certain species of fish. In this decree, 15 species of fish are listed as being the most ciguatoxic.

The fishing and sale of certain species is prohibited everywhere and regardless of the weight of the specimens caught, while for others the restrictions only concern the fishing area or the weight of the individuals caught. Conversely, to date there are no restrictions in Martinique, although the ciguatera incidence rate has been multiplied by 3 in 10 years.

Of the Gambierdiscus observed on the coast of this island could partly explain the cases of poisoning that occurred locally, thus calling into question the local belief as to the origin of ciguatoxic fish in Martinique.

Carmina, a project for the Caribbean basin

Since ciguatera is closely linked to the degradation of marine ecosystems, the study of this intoxication must be understood according to the approach One Health (“One Health”).

Despite the presence of ciguatera risk in the Caribbean, few recent large-scale studies have jointly focused on the study of the diversity, toxicity and toxin profiles of Gambierdiscus. It is in this context that the Carmina project emerged.

The Carmina project is a scientific project funded by the French Development Agency, which aims to study the diversity and toxicity of microalgae responsible for ciguatera in the Caribbean basin.

In collaboration with the laboratories of the NOAA and of thehandlesthe teams of Ifremer aim to improve knowledge of the microalgae associated with ciguatera to enable better risk management in this region.

The species targeted in this study are those belonging to the genus Gambierdiscusbut also those of the genres Fukuyoa and Coolia. Indeed, some metabolites synthesized by Gambierdiscus have been found in some species of the genera Fukuyoa and Cooliasuggesting that they too could contribute to the occurrence of ciguatera.

This project, which involves eleven Caribbean States, began in May 2022 and will strengthen scientific cooperation on the theme of ciguatera, which could increase in the years to come. The first results of this study will be presented at a progress meeting to be held in 2023 in Martinique.