Facts on ciguatera fish poisoning

Disclaimer: The information contained in this factsheet is intended for the purpose of general information and should not substitute individual expert advice or the judgement of healthcare professionals.

Ciguatera fish poisoning (CFP) is a clinical syndrome caused by eating fish that have accumulated ciguatoxins (CTXs) due to feeding on toxic microalgae (Gambierdiscus spp. and Fukuyoa spp.) [1,2]. Traditional endemic regions for ciguatoxic fish include areas in the Caribbean Sea and the Pacific and Indian Oceans, but autochthonous outbreaks have also been reported in Europe (the Canary Islands and Madeira) [3-9]. Outbreaks in mainland European countries have been associated with the consumption of imported fish [10,11].

Ciguatera poisoning is not under routine surveillance in the EU, which is designed for communicable diseases and special health issues like antimicrobial resistance, but all unexpected, potentially serious cross-border biological threats to health are monitored by ECDC [12].

Ciguatoxins (CTXs)

Ciguatoxins (CTXs) activate voltage-gated sodium channels in cell membranes, increasing sodium ion permeability and depolarizing the nerve cell. CTXs are temperature-stable, so they are not destroyed by cooking or by freezing the fish. Furthermore, the toxins are colourless, odourless and flavourless, which make it impossible to taste or smell them [2,13].

Clinical features and sequelae

Clinical presentation varies according to the individual characteristics and the geographical origin of the CTXs. Gastrointestinal symptoms may precede or accompany neurological symptoms, which usually appear three to 48 hours after eating the contaminated fish. Symptoms may include nausea, vomiting, diarrhoea, abdominal cramps, paresthesia of lips, tongue and extremities, cold allodynia (burning pain caused by a normally innocuous cold stimulus), a metallic taste in the mouth, arthralgia, myalgia, pruritus without urticaria or erythema, muscle weakness, blurred vision, painful intercourse, hypotension and bradycardia [1,11,14].

Cold allodynia is considered especially characteristic of CFP, although it is not suffered by all patients. Neurological symptoms usually resolve within weeks, although some symptoms can last for months. Recurrent symptoms may occur following the ingestion of certain food or beverages like alcohol, nuts or non-toxic fish. CFP is rarely fatal, but death can occur in severe cases due to severe dehydration, cardiovascular shock or respiratory failure [1,11,14].

Epidemiology

Ciguatera is one of the most common foodborne poisonings related to finfish consumption but its true incidence is not known. The prevalence in endemic areas ranges from 0.1 percent of the population in continental lands (Queensland [Australia] or Florida [the United States of America]) to more than 50 percent in small South Pacific or Caribbean islands. The traditionally endemic regions are areas of the Caribbean Sea, and the Pacific and the Indian Oceans [1,14,15].

In Europe, several cases of CFP have been reported by travellers to endemic countries as well as through the consumption of imported contaminated fish in the past 20 years [10,11,16,17]. Ciguatera outbreaks due to the consumption of autochthonous fish have also been reported in Madeira (Portugal) and the Canary Islands (Spain) [3-9].

Global environmental changes (including climate change) have had a favourable impact on the distribution and proliferation of the microalgae that produce CTXs [18-20]. In addition, globalization of fish trade may also contribute to the spread of ciguatoxic fish and thus, increasing the risk for poisoning due to consumption of imported fish [10,11].

Transmission

CFP is caused by the consumption of herbivorous fish that feed on toxic microalgae (Gambierdiscus spp. and Fukuyoa spp.), which are attached to macrophytes or dead corals, and from carnivorous fish that have consumed toxic herbivorous fish [1,2].

Over 400 known fish species from tropical and subtropical waters have been classified as potential CTXs carriers. Examples of the fish most frequently associated with cases of ciguatera include barracuda, grouper, amberjack, red snapper, moray eel, hogfish, mackerel, surgeonfish, and parrotfish. Greater severity of illness is associated with eating fish head or organs. It is also advisable to avoid consuming fish viscera (including liver), eggs and skin [1,9].

Person-to-person transmission of CTXs is extremely rare, but transmission from mother to child during breastfeeding or across the placenta, as well as during sexual intercourse, has been described [21-25].

Diagnostics

Reliable laboratory testing to detect CTXs in clinical samples is not currently available, but they can be detected in the fish [26,27]. Semi-quantitative methods including in vitro cytotoxicity or the receptor-binding assays can detect all active toxin analogues that present a CTX-like toxicity. Although these assays do not provide information on toxin profiles, they can be applied as screening methods for CTXs. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods allow specific detection of individual toxin analogues of Pacific, Caribbean and Indian Ocean CTXs, as well as CTXs quantification in fish extracts [28-30]. None of the currently available analytical methods have been formally validated. The maximum limits for CTXs in fish have not been established for regulatory purposes in the EU [26].

The diagnosis in humans is mainly based on recent history of fish consumption and clinical presentation. Diagnosis is supported if several individuals develop similar symptoms and report a common history of seafood consumption. As several other marine toxine poisonings cause partially similar symptoms as CFP, it is important to rule these out by obtaining a thorough history of recent seafood consumption. If the recent seafood consumption history identifies shellfish but not finfish consumption, other marine intoxications are more likely.

Case management and treatment

There is no specific treatment, which is based on symptomatic and supportive care [1,2]. Cases are usually not notified in national surveillance systems but may be reported to national poisoning centres. CFP may cause outbreaks among consumers who have bought marine fish from seafood markets or consumed toxic fish in restaurants. Toxic fish may spread across countries through internal markets once the fish has entered into the EU/EEA. Preventing toxic fish entering markets is the most effective way of preventing outbreaks [31].

Public health control measures

In the event of suspected ciguatera poisoning triggering plans for testing fish, it is advisable to keep any food remnants or parts of the consumed fish frozen at -20ºC, and to contact the local food safety authority.

Fishermen should avoid fishing in areas where cases and outbreaks have occurred or where a suspicion of the presence of ciguatoxin-containing microalgae is reported. These precautions should be taken into account throughout the year, as ciguatera is not seasonal.

Infection control, personal protection and prevention

Avoiding the consumption of large predatory reef fish from affected areas could help prevent ciguatera, although in some areas the consumption of herbivorous fish may also present a high risk for poisoning. Local information about fish species causing ciguatera in the region should be considered and any available instructions by local food safety authorities followed.

Since CTXs may be transmitted through breastfeeding and unprotected sexual intercourse, advice to refrain from breastfeeding and/or sexual intercourse (unprotected) while symptomatic should be considered.

If you suspect you have ciguatera, seek medical attention and consider avoiding the ingestion of certain beverages and food (mainly alcohol, fish and nuts) for six months after the poisoning, as these can cause recurrent symptoms. Patients with ciguatera symptoms should be asked thoroughly about the types of fish they have consumed as well as consumption times and places if possible.

Advice to travellers  

The general recommendation is that travel health physicians and travellers should consult national travel guidelines and recommendations as the primary source of information.

Travellers to endemic areas should be aware of the risks related to the consumption of certain fish species (named above). Fish should only be bought from controlled seafood markets. The identification and removal of toxic fish from the food chain is a priority to prevent the occurrence of further cases.

Further reading

EuroCigua is a joint project by the European Food Safety Authority and Agencia Española de Seguridad Alimentaria y Nutrición (Spain’s Agency for Food Safety and Nutrition)  on the risk characterisation of ciguatera in the European Union/European Economic Area (EU/EEA) [32].

The Food and Agriculture Organization and the World Health Organization’s joint report of the Expert Meeting on Ciguatera Poisoning, Rome 19–23 November 2018, has been published online as part of the AG Food Safety and Quality Series.

 

 

List of references

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