Ciguatera

Worldwide distribution of Gambierdiscus

What is ciguatera?

Ciguatera is the most widespread phycotoxin food-borne disease, endemic in tropical and subtropical areas. It affects every year 25000-500000 people. Ciguatera is caused by eating fish with toxins in their tissues (ciguatoxins produced by microalgae), and typical poisoning can occur at gastrointestinal, neurological and cardiovascular levels. Ciguatera has a low mortality rate but the health problems it causes can last for a long time, and can develop into a chronic illness. In tropical zones where the population is more dependent on fish consumption the incidence of ciguatera is significant and represents a serious problem for health authorities (regions of the Pacific, Caribbean and Indian, mainly).

Ciguatera as an emerging problem

Some species of harmful benthic dinoflagellates of tropical and/or subtropical areas have apparently expanded their distribution over the last decade into temperate regions. In particular, the genus Gambierdiscus responsible for ciguatera, represents a key issue in present harmful algal studies because of the danger it poses to human health. In the Iberian Peninsula, they have so far detected no species of Gambierdiscus but in the Atlantic Ocean, specifically the Macaronesian region, it represents an emerging threat. Gambierdiscus has been recently documented on the island of Madeira and ciguatera cases were recorded in the Savage Islands, between Madeira and Tenerife. The first recorded case of ciguatera in the Canary Islands occurred in 2004 due to amberjack consumption and later, from 2008 onwards, there were more episodes of intoxication. The last recorded episode caused the poisoning of 10 people after dusky grouper consumption in Lanzarote (December 2013).

There is a proposal submitted to the World Health Organization (WHO) in order to consider ciguatera as a neglected tropical disease (http://hab.ioc-unesco.org/index.php?option=com_oe&task=viewDocumentRecord&docID=10751)

Diagnosis and treatment

The diagnosis of ciguatera poisoning is clinical and uses a combination of at least one neurological symptom along with other typical symptoms (diarrhea, vomiting, hypotension) after ingestion of fish. In addition to the direct consumption of fish, there exists some reports of ciguatera transmission through breast milk.

It has also to be considered in the differential diagnosis of gastroenteritis in travelers to endemic areas of ciguatera, and there are cases of ciguatera outside endangered areas, due to the stability of ciguatoxins and the import of contaminated fish.

Symptoms of ciguatera usually manifest at gastrointestinal, cardiovascular and neurological levels. Regarding the neurological symptoms, the most typical are the reversal of hot and cold sensation (dysesthesia, although this is also seen in other poisonings by crustaceans) and loss of sensation in the extremities (paraesthesia). These symptoms may occur after a short period after ingestion (24-48 hours) and usually last one week. However, they may extend intermittently for months or years, as malaise, depression, headaches, muscle aches and fatigue. Cardiovascular manifestations of ciguatera may include bradycardia, hypotension, arrhythmias, and peripheral vasodilatation. Other manifestations include skin irritation and edema, joint pain, weakness, salivation or dry mouth, chills and dysuria.

There is no effective therapy against ciguatera based on commercial drugs or vaccines. Currently, the treatment of choice in acute cases involves the administration of mannitol. Some compounds appear to harbor beneficial properties against the action of ciguatoxins (brevenal, monoclonal antibodies, rosmarinic acid, gabapentin). However, a more complete information about its causes and preventive measures in seafood consumption risk remains the best solution to prevent new outbreaks of ciguatera.

¿Which are the toxins involved in ciguatera?

Toxins involved in ciguatera belong to the group of ciguatoxins. These are complex lipophilic nature polyethers which have been isolated and purified from extracts of fish and microalgae culture. Ciguatoxins are stable to heat and freezing. The first structurally elucidated ciguatoxin in fish was studied Pacific and designated P-CTX-1. For the nomenclature of the CTX’s it is used a code that begins with a letter designating the geographic region:: I-CTX- # to the Indian, C-CTX- # for the Caribbean and P-CTX- # in the Pacific. The numbers are added as there are discovered new analogues for each geographic region.

Variations in toxicity and type of toxins in different regions can contribute to explain the variety of symptoms in the clinical presentation in humans. For example, gastrointestinal disorders seem most important in the Caribbean, while neurological are more common in the Pacific.

Besides ciguatoxins, in Gambierdiscus toxin extracts from French Polynesia were detected gambiertoxins (GTX- #), whose toxic potency is lower than the P-CTX. CTX is believed to be an oxidation product produced from the GTX in Gambierdiscus. In addition to these toxins of lipophilic nature, Gambierdiscus also produces hydrophilic toxins, called maitotoxins and gambieric acid. Maitotoxin is the most potent natural toxin known of non-protein nature, but given its hydrophilic properties is considered to be unrelated to outbreaks of ciguatera in humans.

Ciguatoxins are neurotoxins that affect interneuronal and neuromuscular connections, disrupting nerve conductance and damaging synaptic membranes and myelin sheaths of neurons. Specifically they act on voltage-dependent sodium channels, increasing their permeability, causing numerous effects, including excitability of the neuronal membrane, axonal and Schwann cell edema, increased intracellular calcium, blocking potassium channels and depolarization nervous systems somatic and autonomous.

¿Which algae produce ciguatoxins?

The toxins that cause ciguatera are produced by some species of marine microalgae belonging to the group of the dinoflagellates, in particular the genus Gambierdiscus. These are benthic dinoflagellates whose geographical distribution extends from Ecuador to 40 degrees latitude in both hemispheres.

What is ciguatera?

Ciguatera as an emerging problem

Diagnosis and treatment

¿Which are the toxins involved in ciguatera?

¿Which algae produce ciguatoxins?

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